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NASA's Dawn spacecraft already had an impressive resume when it reachedin early March. Launched in 2007, Dawn is strolling through space, looking deep into the early history of our solar system by studying the asteroid Vesta along with Ceres, its larger sibling. Both are located in the asteroid belt between Mars and Jupiter.
Dawn's earliest views of Ceres were in black and white, showing us a rocky, pockmarked body. Some Dawn's first color map of Ceres, a fascinating enhanced-color image designed to highlight a variety of surface features.showed in these images, giving scientists plenty to ponder as Dawn moved closer to its goal. Researchers shared
"This dwarf planet was not just an inert rock throughout its history. It was active, with processes that resulted in different materials in different regions. We are beginning to capture that diversity in our color images," said Chris Russell, Dawn mission principal investigator.
Scientists believe Ceres is composed of 25 percent water ice by mass. Its most noticeable features are the many craters across the surface. The color map is one tool researchers are using to sleuth out Ceres' history and how impact craters affect the makeup of the surface. The investigation is still in the early stages.
Ceres' bright spots still remain shrouded in mystery, but answers may soon be forthcoming as Dawn enters a new phase in its study of the dwarf planet starting on April 23. It will be within just 8,400 miles of the surface at that time. This will provide scientists with a set of higher-resolution images to work with.
"The bright spots continue to fascinate the science team, but we will have to wait until we get closer and are able to resolve them before we can determine their source," said Russell. | 0.841883 | 3.503063 |
An international team composed of researchers from Finland, France, the United States and the Czech Republic originally set out to construct a state-of-the-art model of the NEO population that is needed for planning future asteroid surveys and spacecraft missions. The model describes the NEOs' orbit distribution and estimates the number of NEOs of different sizes.
The vast majority of NEOs originate in the doughnut-shaped main asteroid belt between the orbits of Mars and Jupiter. The orbit of a main-belt asteroid slowly changes as it is pushed by the uneven release of excess solar heat from the asteroid's surface. The asteroid's orbit eventually interacts with the orbital motions of Jupiter and Saturn changing the trajectory to bring the asteroid close to the Earth. An asteroid is classified as an NEO when its smallest distance from the Sun during an orbit is less than 1.3 times the average Earth-Sun distance.
The team used the properties of almost 9,000 NEOs detected in about 100,000 images acquired over about 8 years by the Catalina Sky Survey (CSS) near Tucson, Arizona, to construct the new population model. One of the most challenging problems facing the team was computing which asteroids they could actually detect. An asteroid appears as a moving point of light against a background of fixed stars but detecting it on an image depends on two factors - how bright it is and how fast it seems to be moving. If the telescope isn't looking in the right location at the right time when an asteroid is bright enough and slow enough to be detected, we simply may never find that asteroid. Accounting for these observational selection effects required a detailed understanding of the operations of the telescope and detector systems and a tremendous amount of computing time even with novel, fast mathematical techniques. The team produced the best-ever model of the NEO population by combining information about CSS's selection effects with the CSS data and theoretical models of the orbit distributions of NEOs that originate in different parts of the main asteroid belt.
But they noticed that their model had a problem - it predicted that there should be almost 10 times more objects on orbits that approach the Sun to within 10 solar diameters. The team then spent a year verifying their calculations before they came to the conclusion that the problem was not in their analysis but in their assumptions of how the Solar System works.
Dr. Mikael Granvik, a research scientist at the University of Helsinki and lead author of the Nature article, hypothesized that their model would better match the observations if NEOs are destroyed close to the Sun but long before an actual collision. The team tested this idea and found an excellent agreement between the model and the observed population of NEOs when they eliminated asteroids that spend too much time within about 10 solar diameters of the Sun. "The discovery that asteroids must be breaking up when they approach too close to the Sun was surprising and that's why we spent so much time verifying our calculations," commented Dr. Robert Jedicke, a team member at the University of Hawai'i Institute for Astronomy.
The team's discovery helps to explain several other discrepancies between observations and predictions of the distribution of small objects in our Solar System. Meteors, commonly known as shooting stars, are tiny bits of dust and rock that are dislodged from the surfaces of asteroids and comets that then end their lives burning up as they enter our atmosphere. Meteors often travel in "streams" that follow the path of their parent object, but astronomers have been unable to match most of the meteor streams on orbits closely approaching the Sun with known parent objects. This study suggests that the parent objects were completely destroyed when they came too close to the Sun - leaving behind streams of meteors but no parent NEOs. They also found that darker asteroids are destroyed farther from the Sun than brighter ones, explaining an earlier discovery that NEOs that approach closer to the Sun are brighter than those that keep their distance from the Sun. The fact that dark objects are more easily destroyed implies that dark and bright asteroids have a different internal composition and structure.
According to Granvik, their discovery of the catastrophic loss of asteroids before a collision with the Sun allows planetary scientists to understand a variety of recent observations from a new perspective but also leads to a more profound advance in asteroid science:
"Perhaps the most intriguing outcome of this study is that it is now possible to test models of asteroid interiors simply by keeping track of their orbits and sizes. This is truly remarkable and was completely unexpected when we first started constructing the new NEO model."
Mikael Granvik, Alessandro Morbidelli, Robert Jedicke, Bryce Bolin, William F. Bottke, Edward Beshore, David Vokrouhlický, Marco Delbò, and Patrick Michel (2016). Super-catastrophic disruption of asteroids at small perihelion distances. Nature 530.
An artist's conception of a complete disintegration of an asteroid as a result of repeated close encounters with the Sun. The actual mechanism causing asteroids to disrupt is still unknown but some obvious scenarios such as tidal forces caused by the Sun and direct sublimation of silicates have been ruled out. One of the remaining scenarios is that volatiles inside the asteroid sublimate at moderate temperatures and create enough pressure to blow up the body. A similar process on a smaller scale called spalling can also break up surface rocks.
Image by Lauri Voutilainen
About the near-Earth-object population modeling project
The project achieved its aim of developing a new near-Earth-object population model that can be used for scientific and technical purposes. The study was conducted by the University of Helsinki (Finland), Observatoire de la Côte d'Azur (France), University of Hawaii (USA), Southwest Research Institute (USA), University of Arizona (USA), and Charles University (Czech Republic). DLR Berlin (Germany) and the University of Braunschweig (Germany) developed infrastructure enabling the utilization of a new NEO model. The project was funded by ESA's General Support Technology Programme (GSTP), NASA's Near Earth Object Observing (NEOO) program, the Academy of Finland and the Czech Science Foundation. Computational resources were provided by CSC - IT Center for Science, Finland, the Finnish Grid Infrastructure and the mesocentre SIGAMM at Observatoire de la Côte d'Azur.
Dr. Mikael Granvik (mobile: +358 50 3182271; email: [email protected])
Dr. Alessandro Morbidelli (email: [email protected])
Dr. Patrick Michel (email: [email protected])
Dr. Robert Jedicke (email: [email protected])
Dr. Ed Beshore (email: [email protected])
Prof. David Vokrouhlický (email: [email protected])
Minna Meriläinen-Tenhu, Press Officer, University of Helsinki, [email protected], +358 50 415 0316, @MinnaMeriTenhu | 0.862345 | 3.986809 |
There really won't be a big bang!
Throughout the year, during most of our public and private programs, we manage to view M31, the Andromeda Galaxy, at the Oregon Observatory. The staff member manning the telescope viewing our neighboring galaxy explains something like: “the M31 galaxy or Andromeda galaxy is our closest visible neighboring galaxy. Andromeda is about two and a half million light years away and is approaching our Milky Way at about 250,000 miles per hour. The two galaxies are due to collide in about 5 billion years.” Sometimes the staff member may go on and explain more or answer questions about this fact. The guest makes appropriate astonished remarks and moves on to another object.
The brief discussion with our visitors is actually echoing the barest minimum of a very complex and fascinating phenomenon that is being studied carefully and intensively by astronomers the world over.
NASA’s official online home to the Hubble Space Telescope is called HubbleSite. Recently, HubbleSite published a detailed description of the pending collision between the Milky Way and the Andromeda galaxy. According to the article: “NASA astronomers announced … they can now predict with certainty the next major cosmic event to affect our galaxy, sun, and solar system: the titanic collision of our Milky Way galaxy with the neighboring Andromeda galaxy…The Milky Way is destined to get a major makeover during the encounter, which is predicted to happen four billion years from now. It is likely the sun will be flung into a new region of our galaxy, but our Earth and solar system are in no danger of being destroyed.”
NASA also produced what is considered an accurate depiction of what the collision event will look like using “painstaking Hubble Space Telescope measurements of the motion of Andromeda.” Computer simulations of Hubble data show that the collision will begin in about four billion years with an additional two billion years before the two galaxies will totally merge.
“Although the galaxies will plow into each other, stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today.”
HubbleSite has produced a video that includes an animated simulation of the collision between the Milky Way and Andromeda. The photos graphically show us what it is likely to look like from the vantage point of earth.
“This illustration sequence depicts the collision of the Milky Way (right) and Andromeda galaxies and shows the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy.”
First Row, Left: Present day.
First Row, Right: In 2 billion years the disk of the approaching Andromeda galaxy is noticeably larger.
Second Row, Left: In 3.75 billion years Andromeda fills the field of view.
Second Row, Right: In 3.85 billion years the sky is ablaze with new star formation.
Third Row, Left: In 3.9 billion years, star formation continues.
Third Row, Right: In 4 billion years Andromeda is tidally stretched and the Milky Way becomes warped.
Fourth Row, Left: In 5.1 billion years the cores of the Milky Way and Andromeda appear as a pair of bright lobes.
Fourth Row, Right: In 7 billion years the merged galaxies form a huge elliptical galaxy, its bright core dominating the nighttime sky.
(Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas, and A. Mellinger)
More information on this and much more Hubble Space Telescope news and photos may be found at the HubbleSite.org. The animated version of the pictured sequence may be found at this link: http://hubblesite.org/news/2012/20 . | 0.842632 | 3.312425 |
Where do you think you’d be more likely to survive if stranded – the moon or Mars?
Before you recall the violent dust storm on Mars that nearly killed Mark Watney in the film The Martian and say “the moon,” let us tell you a story about new research produced by the Planetary Science Lab (PSL) at LSU revealing complex geology on the red planet. Why? Because the moon’s simple geology also means fewer opportunities for the development of life-sustaining minerals such as clays and limestone that typically occur in the presence of water bodies.
“It’s much easier to survive on a complex planetary body bearing the mineral products of complex geology than on a simpler body like the moon or asteroids,” David Susko said. David is a graduate student in the LSU Department of Geology and Geophysics and author of a new study revealing that Mars’ mantle, or the layer between the planet’s crust and its warmer core, may be more complex or complicated than we previously thought. Then again, complex geological processes such as potentially active volcanoes could bring on a whole new set of hazards for martian explorers.
In a paper published today in Nature-affiliated journal Scientific Reports, researchers at LSU document geochemical changes over time in the lava flows of Elysium, a major martian volcanic province. LSU Geology and Geophysics graduate researcher David Susko led the study with colleagues at LSU and beyond, including his advisor Dr. Suniti Karunatillake. They found that the unusual chemistry of lava flows around Elysium is consistent with primary magmatic processes, or processes involving magma under Mars’ crust. These processes could be related to a laterally heterogeneous mantle beneath Mars’ surface or the weight of the overlying volcanic mountain causing different layers of the mantle to melt at different temperatures as they rise to the surface over time.
Elysium is a giant volcanic complex on Mars, the second largest behind Olympus Mons. For scale, it rises to twice the height of Earth’s Mount Everest, or approximately 16 kilometers. Geologically, Elysium is more like Earth’s Tibesti Mountains in Chad, the Emi Koussi in particular, than Everest. This comparison is based on images we have of the region from the Mars Orbiter Camera (MOC) aboard the Mars Global Surveyor (MGS) Mission.
Elysium is unique among martian volcanoes. It’s isolated in the northern lowlands of the planet, whereas most other volcanic complexes on Mars cluster in the ancient southern highlands. Elysium also has patches of lava flows that are remarkably young for a planet often considered geologically silent.
“Most of the volcanic features we look at on Mars are in the range of 3-4 billion years old,” David said. “There are some patches of lava flows on Elysium that we estimate to be 3-4 million years old, so three orders of magnitude younger. In geologic timescales, 3 million years ago is like yesterday.”
In fact, Elysium’s volcanoes hypothetically could still erupt, David said, although further research is needed to confirm this. “At least, we can’t yet rule out active volcanoes on Mars,” David said. “Which is very exciting.” David's work in particular reveals that the composition of volcanoes on Mars may evolve over their eruptive history.
In earlier research led by Suniti Karunatillake, assistant professor in LSU's Department of Geology and Geophysics, researchers in LSU's PSL found that particular regions of Elysium and the surrounding shallow subsurface of Mars are geochemically anomalous, strange even relative to other volcanic regions on Mars. They are depleted in the radioactive elements thorium and potassium. Elysium is one of possibly only two igneous provinces on Mars where researchers have found such low levels of these elements.
“Because thorium and potassium are radioactive, they are some of the most reliable geochemical signatures that we have on Mars,” David said. “They act like beacons emitting their own gamma photons, radiation we can detect, which other elements emit only indirectly. Potassium and thorium also often couple in volcanic settings on Earth.”
In their new paper, David Susko and colleagues started to piece together the geologic history of Elysium, an expansive volcanic region on Mars characterized by strange chemistry. They sought to uncover why some of Elysium’s lava flows are so geochemically unusual, or what makes thorium and potassium levels so low here. Is it because, as other researchers have suspected, glaciers located in this region long ago altered the surface chemistry through aqueous processes? Or is it because these lava flows arose from different parts of Mars’ mantle than other volcanic eruptions on Mars?
Perhaps Mars' mantle has changed over time, meaning that more recent volcanic eruptions differ chemically from older ones. If so, David could use Elysium’s geochemical properties to study how Mars’ bulk mantle has evolved over geologic time, with important insights for future missions to Mars. Understanding the evolutionary history of Mars’ mantle could help us gain a better understanding of what kinds of valuable ores and other materials we could find in the crust, as well as whether volcanic hazards could unexpectedly threaten human missions to Mars in the near future. Mars’ mantle likely has a very different history than Earth’s mantle, because the plate tectonics on Earth are absent on Mars as far as researchers know. The history of the bulk interior of the red planet also remains a mystery.
David and colleagues at LSU analyzed geochemical and surface morphology data from Elysium using instruments on board NASA’s Mars Odyssey Orbiter (2001) and Mars Reconnaissance Orbiter (2006). They had to account for the dust that blankets Mars’ surface in the aftermath of strong dust storms, to make sure that the shallow subsurface chemistry actually reflected Elysium’s igneous material and not the overlying dust.
“The most challenging parts of this research were collecting and analyzing over 400 images of the Elysium Volcanic province,” David said. “Also, the crater counting was painstakingly slow as we logged over 1,300 craters in the region.”
Through crater counting, the researchers found differences in age between the northwest and the southeast regions of Elysium – about 850 million years of difference.
“We were surprised to realize just how young the Southeastern flows are. Some of them are essentially brand new by martian standards,” David said. The researchers also found that the younger southeast regions are geochemically different from the older regions, and that these differences in fact relate to igneous processes, not other processes like the interaction of water or ice with the surface of Elysium in the past.
“We determined that while there might have been water in this area in the past, the geochemical properties in the top meter throughout this volcanic province are indicative of igneous processes,” David said. “We think levels of thorium and potassium here were depleted over time because of volcanic eruptions over billions of years. The radioactive elements were the first to go in the early eruptions. We are seeing changes in the mantle chemistry over time.”
“Long-lived volcanic systems with changing magma compositions are common on Earth, but an emerging story on Mars,” said James Wray, study co-author and associate professor in the School of Earth and Atmospheric Sciences at Georgia Tech. “At Elysium we are truly seeing the bulk chemistry change over time, using a technique that could potentially unlock the magmatic history of many more regions across Mars.”
David speculates that the very weight of Elysium’s lava flows, which make up a volcanic province six times higher and almost four times wider than its morphological sister on Earth, Emi Koussi in northern Chad, has caused different depths of Mars’ mantle to melt at different temperatures. In different regions of Elysium, lava flows may have come from different parts of the mantle. Seeing chemical differences in different regions of Elysium, Susko and colleagues concluded that Mars’ mantle might be heterogeneous, with different compositions in different areas, or that it may be stratified beneath Elysium.
Overall, David's findings indicate that Mars is a much more geologically complex body than originally thought, perhaps due to various loading effects on the mantle caused by the weight of giant volcanoes.
“It’s more Earth-like than moon-like,” David said. “The moon is cut and dry – it lacks the abundance of different mineral types on Earth’s surface. It often lacks the secondary minerals that occur on Earth due to weathering and igneous-water interactions. For decades, that’s also how we envisioned Mars, as a lifeless rock, full of craters with a number of long inactive volcanoes. We had a very simple view of the red planet. But the more we look at Mars, the less moon-like it becomes. We’re discovering more variety in rock types and geochemical compositions, as seen across the Curiosity Rover’s traverse in Gale Crater, and more potential for viable resource utilization and capacity to sustain a human population on Mars. It’s much easier to survive on a complex planetary body bearing the mineral products of complex geology than on a simpler body like the moon or asteroids.”
Susko plans to continue clarifying the geologic processes that cause the strange chemistry found around Elysium. In the future, he will study these chemical anomalies through computational simulations, to determine if recreating the pressures in Mars’ mantle caused by the weight of giant volcanoes could affect mantle melting to yield the type of chemistry observed within Elysium.
“The most rewarding part of this research for me was being able to work to piece together a geologic history for a specific region on a planet that is over 100 million miles away from us,” David said. “It makes looking at Mars through telescopes here on Earth much more personal.”
Study: Susko et al. (2017) A record of igneous evolution in Elysium, a major martian volcanic province. Scientific Reports 7.
David Susko led this study with LSU undergraduate student Taylor Judice, mentored by their advisor Suniti Karunatillake. This multi-institutional and international investigation was co-authored by Gayantha Kodikara at the University of Ruhuna in Sri Lanka; John Roma Skok, SETI Institute; James Wray at Georgia Institute of Technology; Jennifer Heldmann at NASA Ames; and Agnes Cousin at the Institut de Recherche en Astrophysique et Planétologie in France. NASA’s Mars Data Analysis Program (MDAP) funded the project at LSU, which used data from several missions, including the 2001 Mars Odyssey Gamma Ray Spectrometer (GRS) and the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (MRO). | 0.820299 | 3.740829 |
IRF-U Space Plasma Physics
| INSTITUTET FÖR RYMDFYSIK
| Swedish Institute of Space Physics
|| (59o50.272'N, 17o38.786'E)
the research programme
Space Plasma Physics
We investigate what
goes on in space using instruments we build
ourselves and fly on spacecraft, ground based instruments, computer
simulations and plasma theory. Here are some samples of our research:
For the moment,
we have seven instruments in
various parts of the solar system, and four more to which we have made
a significant contribution.
- Oct 2016: In a paper in Physical
Review Letters, our PhD student
Andreas Johlander have used the Magnetospheric Multiscale (MMS) satellites
to find out the details of shock waves in space. See also our
- Oct 2016: In a paper in Journal of Geophysical Research, our PhD student
suggests new ways electrons can be accelerated in a shocked solar wind, based on the Magnet
ospheric Multiscale (MMS) satellite data. The paper was selected as Editor's High
- May 2014: The properties of asymmetric magnetic reconnection, important for storage and release
of magnetic energy in a variety of cosmic contexts, could be explored in detail
with our and other instruments on ESA's Cluster satellites. The results were
published in Physical Review Letters.
- Jul 2013:
Magnetic reconnection can be more efficient in accelerating electrons to
high energy when variable rather than steady, we show in a paper in
- Aug 2012:
Exploring the properties of thin sheets in space, we have for the first time been able
to verify the properties of so called lower hybrid drift waves in space around Earth,
using our instruments on the multi-spacecraft Cluster mission.
The results were published in Physical Review
Letters: see also our press release.
- Jan 2012: Cold plasma previously hidden in the magnetosphere is revealed by our instruments on
the Cluster satellites in a study we publish in Geophysical Research Letters,
also featured in National Geographic Daily News and an AGU news release.
- Jan 2012: We show that dusty plasma around Enceladus affects
Saturn's magnetosphere. See the NASA mission news feature or the editor's highlight in Journal of
- Jul 2011: Plasma jets are common in the universe, and now we know the details of what happens
when they hit an obstacle, using our instruments on the Cluster satellites
in the Earth's magnetic tail.
highlights the study, published in Physical Review Letters.
- Oct 2010: Small pulse-like waves
known as electron holes dwell at the heart of a
magnetically explosion in space, known as reconnection, we show from
our Cluster data in study in
Letters. See also our press release.
- Oct 2010: We contribute to a study in
Science showing th
at pulsating aurora is caused by waves in space known as chorus emissions. See also the
National Geographic news feature.
- March 2010: Pressure fronts in the solar wind help erode the
atmosphere of Mars, we show in Geophysical
See also our press
- July 2009: How is the solar wind heated? Part of the answer is
turbulence, as shown in a study in Physical Review Letters. See also NASA's and ESA's press releases.
- March 2009: Is space turbulent? Yes! In a study
Review Letters, we present detailed Cluster studies of turbulence
in space. See ESA's press
- Dec 2008: We have tracked a previously invisible ion wind from
the Earth far out in space using Cluster. Published in Nature
Geoscience, presented in our press
release and in an ESA Cluster
- March 2007: We found that magnetic field reconnection occurs in
turbulent plasmas, too. Published in Nature Physics,
presented in an ESA news
- Nov 2006: We reveal the inner structure of a region of space
close to a magnetic reconnection site. Published in Physical Review
- Aug 2005: We discovered Alfvén vortices, a kind of
whirlpools in space, near the boundary of the Earth's magnetosphere.
Published in Nature, presented in
release and in an ESA news feature.
- May 2005: On arrival at Saturn, our Langmuir probe on Cassini
immediately detected cold plasma around Titan and plasma interaction
with ring dust. Published in Science and Geophysical Research
instruments in space, no longer operational:
- BepiColombo -- an ESA-JAXA (Europe-Japan) mission to Mercury, where we are
responsible for the electronics and probe surfaces
for the MEFISTO sensors of the PWI instrument on the magnetospheric orbiter. Launch 2018, orbit insertion
at Mercury 2024. More
on Bepi and MEFISTO at KTH.
- Solar Orbiter -- ESAs mission to investigate the Sun at close distance, for launch in 2018. We are building parts
of the RPW instrument to study the solar wind close to its source.
- JUICE -- ESA's Jupiter Icy Moons Explorer mission. Together with a large team of European, Japanese and American laboratories, we will provide instrumentation for investigating waves, fields and plasmas in the Jovian system. Launch 2022, arrival at Jupiter in 2030.
- Cassini --
launched by NASA in 1997,
explored the environment of Saturn 2004-2017, with our Langmuir
- Rosetta --
carried our instrument in orbit around comet 67P/Churyumov-Gerasimenko, launched by ESA in 2004, impact landing on the comet 30 September 2016.
-- orbited the moon with our Langmuir probes onboard,
launched September 2003, impact landing on the moon 3 September 2006
microsatellite (only 29 kg) carrying our LINDA instrument to the
upper ionosphere 1998-1999
- Freja -- detailed
of the Earth's upper ionosphere 1992-1996, including our wave
- Viking --
magnetosphere 1986-1987 by means of our wave instrument (and of course
other instruments as well)
- Numerous sounding rockets during the sixties, seventies, and eighties.
Engineers and computing support:
- Mats André, PhD, professor -- head of research
- David Andrews, PhD -- scientist (Cassini, Mars)
- Jan Bergman, PhD -- scientist, JUICE RPWI project manager
- Stephan Buchert, PhD -- scientist (Swarm)
- Niklas Edberg, PhD -- scientist (Cassini, Rosetta)
- Anders Eriksson, PhD -- scientist (Rosetta, Cluster)
- Daniel Graham, PhD -- scientist (Cluster, MMS)
- Lina Hadid, PhD -- postdoc (Cassini)
- Yuri Khotyaintsev,
PhD, docent -- scientist (Cluster, MMS)
- Wenya Li, PhD -- postdoc (Cluster, MMS)
- Michiko Morooka, PhD -- scientist (Cassini)
- Hermann Opgenoorth, PhD, professor -- magnetospheres and ionospheres at Earth and other planets
- Andris Vaivads,
PhD, docent -- Solar Orbiter lead CoI, Cluster, MMS
- Erik Vigren, PhD -- scientist (Cassini, Rosetta)
- Jan-Erik Wahlund, PhD, docent -- JUICE RPWI PI, Cassini
RPWS-LP lead CoI, BepiColombo lead CoI
- Emiliya Yordanova, PhD -- scientist (MMS, Cluster)
students (see also our PhD projects page):
- Martin Berglund, PhD, research engineer -- electronics
- Vicki Cripps, research engineer -- PA/QA
- Jesper Fredriksson, research engineer -- analog electronics
- Reine Gill, research engineer -- flight s/w, s/c operations
- Sven-Erik Jansson, senior research engineer -- digital electronics
- Erik Johansson, PhD, research engineer -- Cassini and Rosetta data handling
- Jan Karlsson, programmer -- data archiving and computer systems
- Thomas Nilsson, research engineer -- Swarm and MMS data handling
- Walter Puccio, senior research engineer -- electronics
- Farid Shiva, research engineer -- electronics design and
- Hon Ching Wong, research engineer -- flight s/w
(see also our student projects page):
- Ilka Engelhardt -- plasma and dust around icy moons and comets (Cassini/Rosetta)
- Elin Eriksson -- energy conversion in space plasma (MMS, Cluster)
- Fredrik Leffe Johansson -- electrostatic probes in space (Rosetta and other)
- Andreas Johlander -- particle energization at shocks (MMS, Cluster)
- Elias Odelstad -- cometary plasma environment (Rosetta)
- Oleg Shebanits -- pre-biotic conditions at Titan (Cassini)
last modified on Friday, 15-Sep-2017 19:17:08 CEST | 0.86074 | 3.155186 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2009 March 22
Explanation: The Sun destroyed this comet. Arcing toward a fiery fate, this Sungrazer comet was recorded by the SOHO spacecraft's Large Angle Spectrometric COronagraph(LASCO) on 1996 Dec. 23. LASCO uses an occulting disk, partially visible at the lower right, to block out the otherwise overwhelming solar disk allowing it to image the inner 5 million miles of the relatively faint corona. The comet is seen as its coma enters the bright equatorial solar wind region (oriented vertically). Spots and blemishes on the image are background stars and camera streaks caused by charged particles. Positioned in space to continuously observe the Sun, SOHO has now been used to discover over 1,500 comets, including numerous sungrazers. Based on their orbits, they are believed to belong to a family of comets created by successive break ups from a single large parent comet which passed very near the Sun in the twelfth century. The Great Comet of 1965, Ikeya-Seki, was also a member of the Sungrazer family, coming within about 650,000 kilometers of the Sun's surface. Passing so close to the Sun, Sungrazers are subjected to destructive tidal forces along with intense solar heat. This comet, known as SOHO 6, did not survive.
Authors & editors:
Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
A service of: ASD at NASA / GSFC
& Michigan Tech. U. | 0.859705 | 3.207928 |
WISE to Start Today
NASA's WISE Set to Blast Off and Map the Skies
"The last time we mapped the whole sky at these particular infrared wavelengths was 26 years ago," said Edward (Ned) Wright of UCLA, who is the principal investigator of the mission. "Infrared technology has come a long way since then. The old all-sky infrared pictures were like impressionist paintings - now, we'll have images that look like actual photographs."
At liftoff, the main Delta II engine and three solid-motor boosters will ignite, providing a total liftoff thrust of more than 1,812,000 newtons (407,000 pounds). The rocket will tilt toward the south, cross the California coastline and head out over the Pacific Ocean. At one minute and 39 seconds after launch, the three spent boosters will fall away from the rocket. Two minutes and 45 seconds later, the main engine will cut off, and 14 seconds later, the vehicle's second stage will ignite. At four minutes and 56 seconds after liftoff, the "fairing" covering the satellite will split open like a clam shell and fall away.
The second stage of the rocket will then cut off, reigniting again 52 minutes after launch. It will shut down a second time and then, at about 55 minutes after launch, the spacecraft will reach its final orbit and separate from the rocket. Engineers expect to pick up a signal from WISE anywhere from about one to 10 minutes after separation.
The next major event will occur about 20 minutes after separation - the valves on the spacecraft's cryostat will automatically open. The cryostat houses and chills the telescope and infrared detectors with tanks of frozen hydrogen. Valves on the cryostat are opened after launch to allow boiled-off hydrogen to escape, thereby preventing the instrument from warming up.
After the spacecraft is checked out and calibrated, it will begin the task of surveying the whole sky. This will take about six months, after which the spacecraft will begin to sweep the sky a second time, covering about one-half before the frozen coolant runs out. The mission's primary lifetime is expected to be about 10 months.
The closest of the mission's finds will be asteroids and comets with orbits that come relatively close to Earth's path around the sun. These are called near-Earth objects. The infrared explorer will provide size and composition information about hundreds of these objects, giving us a better idea of their diversity. How many are dark like coal, and how many are shiny and bright? And how do their sizes differ? The mission will help answer these questions through its infrared observations, which provide information that can't be obtained using visible-light telescopes.
"We can help protect our Earth by learning more about the diversity of potentially hazardous asteroids and comets," said Amy Mainzer.
The farthest of the mission's targets are powerful galaxies that are either churning out loads of new stars or dominated by voracious black holes. These galaxies are shrouded in dust, and often can't be seen in visible light. WISE will expose millions, and may even find the most energetic, or luminous, galaxy in the universe.
"WISE can see these dusty objects so far away that we will be looking back in time 10 billion years, when galaxies were forming," noted Peter Eisenhardt. "By scanning the entire sky, we'll learn just how extreme this galaxy formation process can get." | 0.863247 | 3.495363 |
The Square Kilometre Array (SKA) is the world’s largest radio telescope project, which will collect data over one million square kilometres from radio astronomy telescopes on the African and Australian continents. In the long run the two-phased SKA could possibly help scientists answer questions in astrophysics, cosmology and fundamental physics. Phase one of the project entailed setting radio telescopes in South Africa and Australia. Phase two will include more telescopes being added by partner countries, New Zealand and the eight African countries namely: Botswana, Ghana, Kenya, Mauritius, Madagascar, Mozambique, Namibia and Zambia. The full array should be up and running by 2030, but the first phase is expected to be operational by 2023. The launch of Ghana’s radio telescope is a critical part of this process. Dr Bernard Duah Asabere explained its significance.
How did Ghana get involved in the project and how does it fit in?
Ghana has had a redundant satellite communication antenna in Kutunse – a suburb 25 kilometres north-west of the capital, Accra.
Between 2011 and 2017 this antenna has been undergoing refurbishment for use as a radio astronomy telescope. At the end of the first engineering phase, the refurbished telescope is capable of participating in global network observations using a technique known as Very Long Baseline Interferometry (VLBI). It also be used in single dish or standalone operational mode.
Interferometry is a technique in which collections of telescopes scattered over a large area function as a single radio telescope. The Very Long Baseline Interferometry technique is most well-known for:
imaging distant cosmic radio sources,
tracking spacecraft, and
for applications in astrometry.
But the technique can also measure the time differences between the arrival of radio waves from separate antennas to the same source in the sky. This helps astronomers get a better image resolution of an object or a region in the universe.
Put simply, if different telescopes at different locations are all tuned to observe the same source in the sky at the same time, astronomers can get fine details of the specific object being observed.
The countries that make up the African SKA project are each building their own radio telescopes or converting redundant telecommunication dishes so that they function as a network known as the African VLBI Network (AVN).
Ghana now becomes the first country in the African SKA partners besides South Africa to have a telecommunication antenna converted to realise the African VLBI Network. With Ghana’s telescope now operational, it means that South Africa and Ghana will be able to do joint observations. When the other seven African SKA partner countries get theirs ready, they will join the African’s network.
Kenya, Mozambique and Zambia are contending to add the next telescope to the network.
How did we know the Ghanaian telescope was ready and what will it do?
Across the globe there are several very long base interferometry networks: Europe has one, as does Australia and America. Any telescope across the world is able to join an observation in one of these networks.
After Ghana re-engineered the antenna into a functional radio astronomy telescope, it needed to do a science commissioning of the facility to see if the refurbishment was successful and it could track and observe astronomical sources in the sky and join international observations.
When Ghana tested its telescope it was able to detect methanol masers, observe pulsars and also succeeded in participating in an observation with 15 other telescopes which form part of the European very long base interferometry network.
Until now South Africa has been the only country on the continent that had been joining in VLBI observations with other countries’ networks because it was the only country with a radio telescope on the continent.
With radio telescopes in Ghana and South Africa, an African network is now given birth to. Aside being a part of the African network, Ghana could join other telescopes on the globe to do science observations.
What is the significance of Ghana’s telescope for astronomy in Africa?
There are many celestial objects to observe in the Universe: planets, masers, galaxies, meteorites, stars and even regions in the sky. And there are global questions that astronomy community is interested in addressing. This includes questions like: is there any life outside earth? Are there other stars that are as prominent as the sun? How did the universe come into being? These are questions that the SKA will attempt to address.
If Africa has its own network, astronomers on the continent can choose what celestial objects and regions it wants to observe.
If we look at most of the existing telescopes across the world, there has been a hole in Africa. Telescopes situated in the Northern hemisphere are unable to see the region of the sky in the southern hemisphere. With an African very long base interferometry network set up, astronomers in Africa can now observe both the northern and southern hemispheres of the sky from the continent.
What is Ghana bringing to the party and what does it hope to get out of this SKA collaboration?
The facility at Kutunse will be used as a science instrument but also as a training facility. Ghana will help the other seven countries that form part of the African network refurbish their unused antennae.
Although this technology is not new and has been done in Australia, Peru, Japan and the UK, no other country in Africa has done this.
For Ghana, developing the skills, regulations and institutional capacity in the partner countries is a vital part of building the square kilometre array on the continent over the next decade. This is because it will optimise African participation in the SKA.
Ghana will build it robust research community in a field never before accessible to the country.
But there is also the prospect of improving the radio astronomy capacity in the country. Ghana’s radio astronomy development strategy forms part of the broader Ghana Science, Technology and Innovation Development Plan. | 0.843627 | 3.577189 |
“Ocean Worlds” discoveries build case for new missions
WASHINGTON — Discoveries involving two “ocean world” moons in the outer solar system announced April 13 are likely to bolster the case for planned and proposed spacecraft missions to those worlds.
At a press conference, NASA announced that its Cassini spacecraft, orbiting Saturn, had detected hydrogen gas in previously-discovered plumes emanating from the surface of the icy moon Enceladus. Scientists suspect that the moon has an ocean of liquid water beneath the surface that provides the source material for the plumes.
The hydrogen, scientists said at a briefing, is likely produced by hydrothermal activity, and could serve as an energy source for any life there. “Although we can’t detect life, we’ve found that there’s a food source there for it. It would be like a candy store for microbes,” said Hunter Waite, team lead for Cassini’s ion and neutral mass spectrometer, in a statement about the discovery.
In a separate finding presented at the same briefing, scientists using the Hubble Space Telescope detected new evidence of plumes emanating from Europa, the icy moon of Jupiter also thought to have a subsurface ocean. Such plumes had been seen in past Hubble observations of the moon, but limited data, in part because the plumes appear to be intermittent, had left some scientists skeptical about whether they exist.
The new observations give scientists greater, but not complete, confidence Europa has plumes. William Sparks, an astronomer with the Space Telescope Science Institute, said at the briefing the detection was made at the “four sigma” level of confidence, which made it unlikely, but not impossible, that the detections were simply random noise or instrumental effects.
“That’s not quite as strong evidence as you’d really like,” he acknowledged. “I wouldn’t say it’s completely unequivocal the way it is with Enceladus. We’re still at the limits of what Hubble can do. But we’re growing in confidence.”
Follow-up observations will require new missions. NASA is already developing a mission to Europa, called Europa Clipper, that will go into orbit around Jupiter and make dozens of close flybys of the moon to better determine how habitable it is.
Among the suite of instruments on Europa Clipper is an ultraviolet spectrometer. “This imager is going to be the plume finder,” said Jim Green, director of NASA’s planetary science division.
He added that, hopefully, the spacecraft will be able to fly through a plume, much as Cassini did at Enceladus. “Now we’ll have the right set of observations to make,” he said. That includes an advanced mass spectrometer that will be able to measure the composition of the plume.
Europa Clipper is being developed for launch as soon as 2022, and could arrive at Jupiter in late 2024, depending on the choice of launch vehicle. However, scientists acknowledge that it’s unlikely that the spacecraft will alone be able to determine if there is life in Europa’s oceans. A follow-on lander mission is in the early stages of development, although the Trump administration’s fiscal year 2018 budget blueprint, released March 16, included no funding for a lander despite supporting Europa Clipper and other planetary programs in that budget proposal.
The prospects for missions to Enceladus are less clear. Cassini is nearing the end of its mission, as NASA plans a final series of close-in investigations of Saturn and its rings prior to flying the spacecraft into Saturn itself in mid-September. With Cassini running low on fuel for its thrusters, that maneuver is intended to prevent the spacecraft from possibly crashing into, and contaminating, the potentially habitable moons of Enceladus and Titan.
Cassini also lacks the instrumentation to better understand if Enceladus is inhabited. “Cassini can look for habitability, but we don’t have the instruments to look for life,” said Linda Spilker, Cassini project scientist, at the briefing. “We’ve come as far as we can go, so it remains for a future mission to detect life at Enceladus.”
NASA currently has no mission to Enceladus, or Saturn in general, on the books. However, so-called “ocean worlds,” which include Enceladus and Titan, are one of the proposed destinations for the next mission in the New Frontiers program of medium-class planetary missions. NASA issued an announcement of opportunity for that next mission late last year, with proposals due to NASA April 28. The agency expects to select several proposals in November for additional study, with a final selection in mid-2019.
Congress, in its fiscal year 2016 appropriations bill, directed NASA to develop an “Ocean Worlds Exploration Program” to search for life on such worlds using a mix of small and large missions. That language was included by Rep. John Culberson (R-Texas), chairman of the appropriations subcommittee that funds NASA and a strong advocate for missions to Europa in particular.
A formal program is still being established within the agency, officials said at the briefing. Mary Voytek, astrobiology senior scientist at NASA Headquarters, said a “roadmap” document outlining studies of ocean worlds is in the final stages of development by an advisory group. “They’re about to deliver that to us any day now,” she said. That document, she said, will set science priorities and technology requirements for any future missions.
Some scientists have questioned whether Enceladus, with its constant plumes containing chemical energy that could support life, may be a better initial target than Europa. Voytek noted that the presence of hydrogen in the plume indicates that it is not being consumed by any life that might exist in the oceans in Enceladus. “It means that there might not be life there at all, and if there is life, it’s not very active,” she said.
She speculated that could be linked to the age of Enceladus, which may be much younger Saturn itself. Europa, by contrast, was formed at the same time as Jupiter, more than four billion years ago. “That’s a lot more time for life to have emerged and start taking advantage of these energy sources,” she said. “So my money, for the moment, is still on Europa.”
Source: Space News
14 Apr, 2017
“Ocean Worlds” discoveries build case for new missions
Posted in Space News and tagged Space by cnkguy with no comments yet. | 0.84142 | 3.283914 |
There are about two dozen so-called hypervelocity stars known to be escaping our Milky Way galaxy, but PB 3877 is the first wide binary star found to travel at such a high speed. The results of a new study challenge the commonly accepted scenario that hypervelocity stars are accelerated by the supermassive black hole at the galactic centre.
Zooming in on black holes is the main mission for the newly installed GRAVITY instrument at ESO’s Very Large Telescope in Chile. During its first observations, GRAVITY successfully combined starlight using all four 1.8-metre Auxiliary Telescopes. The first observations using GRAVITY with the four 8-metre VLT Unit Telescopes are planned for later in 2016.
Researchers from Australia and the USA have discovered a distant, ancient cloud of gas that may contain the signature of the very first stars that formed in the universe. The gas cloud is many billions of light-years away from Earth, and is observed as it was just 1.8 billion years after the Big Bang.
NASA’s Swift spacecraft has detected its 1,000th gamma-ray burst (GRB). A GRB is a fleeting blast of high-energy light, often lasting a minute or less, occurring somewhere in the sky every couple of days. GRBs are the most powerful explosions in the universe, typically associated with the collapse of a massive star and the birth of a black hole.
Astronomers using NASA’s Hubble Space Telescope and ESO’s Very Large Telescope in Chile have discovered never-before-seen moving features within the dusty disc surrounding the young, nearby star AU Microscopii. The fast-moving, wave-like structures are moving at 22,000 miles per hour — fast enough to escape the star’s gravitational pull. | 0.896228 | 3.63686 |
Robert Michael / AFP - Getty Images
A nearly full moon rises behind the cross of the Frauenkirche in the German city of Dresden in May 4.
Saturday night's "supermoon" is the biggest and brightest full moon of the year, due to the fact that the moon is near the closest point in its orbital path around Earth. But just how much bigger and brighter does it look? That's a tricky question.
Most reports say the moon looks 14 percent bigger than usual, which is close to the truth but isn't quite right. They also say it's 30 percent brighter than usual, which isn't right, either. James Garvin, chief scientist at NASA's Goddard Space Flight Center, ran the numbers to come up with an explanation that seems to make the most sense.
First of all, it's important to note that the moon itself is not getting significantly bigger or smaller. There's a scientific debate over whether the moon is slowly shrinking or spreading out. But in either case, the change isn't noticeable on human time scales.
The difference in the moon's apparent size is basically a function of how close it is to Earth in its elliptical orbit. That orbit isn't changing on human time scales, either. It just so happens that tonight, the moon is coming closest to Earth at the same time that it's going full. Because the moon and the sun are precisely opposite each other, relative to Earth, tonight's ocean tides may be a bit higher than typical — but again, the effect is nowhere near big enough to worry about.
So how noticeable is the visual effect? Here what Garvin told me in an email today:
- "The biggest predictable effect on the brightness of the full moon is how close the moon is to Earth. With everything else the same, a full moon is about 30 percent brighter when the moon is closest to Earth in its orbit (called perigee) compared to a full moon when the moon is farthest from Earth in its orbit (called apogee). Today’s full moon is at perigee."
- "Also, when the moon is high in the sky (as it is now), we are closer to the moon by approximately the radius of Earth compared to when the moon is on the horizon. (Note: Earth’s radius is about 6,371 kilometers)."
- "Since the distance from the center of Earth to the center of the moon is on average about 384,403 kilometers, the radius of the earth is about 6,371 kilometers, and brightness changes as the square of the distance, being closer to the moon by about the radius of the earth increases the brightness of the full moon by about 3 percent."
- "Thus the present supermoon is, at maximum, only about 9 to 10 percent larger in an angular (appearance) sense than a typical full moon and is also brighter (by a few percent), making it appear 'super.'"
"Meanwhile, our intrepid Lunar Reconnaissance Orbiter continues its remarkable mapping of our nearest celestial neighbor, coming up (in June) on its three-year anniversary of being in lunar orbit with its amazing array of 7 instruments," Garvin added. "As of now, the data returned from LRO (over 300 trillion bytes) is larger than all of the rest of the data acquired for planets in the solar system combined (except for Earth, of course)."
Which just goes to show that every day is a "super moon" day for the Lunar Reconnaissance Orbiter and its science team. Check out NASA's Web site for more wisdom from James Garvin.
A NASA video explains the science behind the "supermoon."
Geoff Chester, an astronomer at the U.S. Naval Observatory, says the moon appears 14 percent larger in angular size when it's at the closest point in its orbit, compared with its appearance when it's farthest away from Earth. That's not 14 percent larger than average. That's 14 percent larger than the minimum apparent size.
"You'd be very hard-pressed to detect that with the unaided eye," Chester told The Associated Press. Seasoned skywatchers, however, say they can definitely tell the difference. Can you? Take a look at the moon tonight — before, during or after the moment of maximum fullness at 11:35 p.m. ET — and tell us what you see.
Update for 6:45 p.m. ET May 5: Bad Astronomy's Phil Plait observes that the moon's angular size is roughly equivalent to that of a dime as seen from 6 feet away. You can bet I'll have a dime taped onto a south-facing window tonight to make the observations. Also, tonight's supermoon will be a little less super than last year's supermoon, because the moon is about 240 miles farther away at peak fullness than it was in March 2011. For what it's worth, next year's supermoon will be imperceptibly smaller than this year's. I wonder if there'll be perceptibly less hype.
Update for 2:20 a.m. ET May 6: Yes, the weather was clear enough for supermoon-gazing in my Seattle-area neighborhood — and yes, I really did tape a dime onto a window to compare its angular size with the moon's. But it seemed to me that the sizes were about the same at a dime distance of 4 or 5 feet, rather than the 6-foot distance that Phil Plait suggested. Which just goes to show you: YMMV (your moon may vary). You can see what I saw by checking my Twitpic gallery.
More about the supermoon:
- How to see the supermoon — and meteors, too
- How to plan your supermoon snapshot
- Supermoon rises over Greek temple
- Five moon mysteries
- Five moon myths
If you snap a great photo of the moon, feel free to upload it into msnbc.com's FirstPerson in-box.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds. | 0.880247 | 3.73848 |
1.2.6 Synchronous rotation
Because most moons in the Solar System are in close orbit around much larger planetary bodies, over time the speed of a moon’s rotation is decreased as the tidal, or gravitational, pull between the two bodies drags on the moon’s spin. Eventually, this slows down a moon’s rotation so much that it completes only one rotation about its axis per orbit, resulting in the same side of the moon facing its planet at all times (known as captured rotation, or synchronous rotation). With the Earth and the Moon, these competing tidal forces have also exerted drag on the Earth’s rotation, slowing its rate of spin about its axis and thus lengthening a day by almost two milliseconds per century.
Tidal forces affect you too. While standing on the Earth’s surface, your head is nearly two metres further away from the centre of the Earth than your feet are. The Earth’s gravitational field can be treated as if all the mass were concentrated at the planet’s centre. Since the force of gravity decreases as the distance increases, your feet are pulled down slightly more strongly than your head. The anatomical consequences of this stretching are negligible for you, but for a much more extended body such as a moon, the physical consequences can be quite noticeable and in one case, as you will see later, very severe. | 0.884556 | 3.409088 |
In 1828 the Royal Astronomical Society awarded its gold medal to Caroline Herschel, the first woman to receive the prize. It wouldn't be awarded to another woman until 1996.
Herschel was also the first woman to be paid for her contribution to science for the discovery of six new comets.
On what would be her 266th birthday, Herschel has been honoured with a Google Doodle. The Doodle shows Herschel searching the skies for comets through her telescope.
Who was Caroline Herschel?
Born in Hanover, Germany in 1750, Herschel was the eighth child of a rural German family. When she was 10 years old Herschel fell ill with typhus, which stunted her growth and left her scarred. She never grew taller than 4 ft 3 in and it was assumed she would never marry.
After a difficult childhood Herschel moved to England to join her brother William Herschel in Bath when she was 22. She began to train as a singer, and sang as a soprano in many performances. Having started his career as a musician, William soon developed a passion for astronomy, which he shared with his sister.
In 1781 William discovered the planet Uranus. Following this major discovery, he was knighted and appointed to the position of King's Astronomer for George III. Herschel, who was in her early thirties by then and still living in England, travelled with her brother and became his assistant.
In this role, Herschel began to make astronomical observations on her own. Then, in the summer of 1786, she made a discovery that no woman had made before her - she discovered a comet. Comets are made up of gas and ice, and have and often have a long tail, or coma. They differ from asteroids, which are made up of rock and metal.
Touch image to enlarge
Herschel's many astronomical discoveries
Herschel went on to discover seven comets, five of which she is given full credit for. Several of the comets she discovered, such as the 35P/Herschel-Rigollet comet, which was last seen in 1939, were named after her. She spotted the first from Slough in 1788.
The moon crater C. Herschel was also named after her, as was the asteroid 281 Lucretia - her second given name.
In recognition of her work as William's assistant, King George III started paying Herschel a salary of £50 (the equivalent of £5,700 in 2016) a year. This made her the first woman to be paid for her contribution to science.
In another first, Herschel was awarded the Royal Astronomical Society's top prize in 1828 for producing a catalogue of nebulae (interstellar clouds of dust, hydrogen, helium and other ionised gases). The next woman to win the gold award was Vera Rubin in 1996.
A year before her death, when Herschel was 96 and living in Hanover again, she was awarded a Gold Medal for Science from the King of Prussia. It was given to her "in recognition of the valuable services rendered to Astronomy by you, as the fellow-worker of your immortal brother, Sir William Herschel, by discoveries, observations, and laborious calculations".
Famous British women that pioneered in science and maths
- Mary Somerville (1780-1872) was named an honorary member of the Royal Astronomical Society alongside Herschel in 1833 for her work as a pioneering mathematician and scientist. Somerville, who lived to be 91, had a college at Oxford University named after her.
- Ada Lovelace (1815-1852) created what is regarded as the world's first computer program, which was in fact a method for calculating a sequence of numbers. She was the daughter of poet Lord Byron, but she never knew him.
- Florence Nightingale (1820-1910) is the founder of modern nursing and a pioneer of using visuals to present statistical information. Through her graphics she managed to persuade the UK Government that it needed to change.
- Rosalind Franklin (1920-1958) was one of the biophysicists that contributed to the understanding of the molecular structures of DNA. Her work helped in the discovery of the DNA double helix.
- Dorothy Hodgkin (1910-1994) is the only British woman to receive a Nobel Prize for science for her pioneering work into the structures of vitamin B12 and penicillin. She also discovered the structure of insulin.
- Joan Clarke (1917-1996) was the only female code-breaker to work at Bletchley Park during World War Two alongside Alan Turing. She went on to work at GCHQ.
- Dame Jane Goodall is the world's greatest expert on chimpanzees.
- Dame Jocelyn Bell Burnell discovered the first ever recording of a pulsar (rapidly rotating neutron star) when she was studying for her PhD. She was famously overlooked for a Nobel Prize for this work. Burnell became the first female president of both the Royal Society of Edinburgh and the Institute of Physics, and was made a dame in 2007. | 0.907175 | 3.100576 |
Scientists using images from NASA's Mars Reconnaissance Orbiter, or MRO, have estimated that the planet is bombarded by more than 200 small asteroids or bits of comets per year forming craters at least 12.8 feet (3.9 meters) across.
Researchers have identified 248 new impact sites on parts of the Martian surface in the past decade, using images from the spacecraft to determine when the craters appeared. The 200-per-year planetwide estimate is a calculation based on the number found in a systematic survey of a portion of the planet.
The University of Arizona's High Resolution Imaging Science Experiment, or HiRISE camera, took pictures of the fresh craters at sites where before and after images had been taken. This combination provided a new way to make direct measurements of the impact rate on Mars and will lead to better age estimates of recent features on Mars, some of which may have been the result of climate change.
"It's exciting to find these new craters right after they form," said Ingrid Daubar of the UA, lead author of the paper published online this month by the journal Icarus. "It reminds you Mars is an active planet, and we can study processes that are happening today."
These asteroids or comet fragments typically are no more than 3 to 6 feet (1 to 2 meters) in diameter. Space rocks too small to reach the ground on Earth cause craters on Mars because the Red Planet has a much thinner atmosphere.
HiRISE targeted places where dark spots had appeared during the time between images taken by the spacecraft's Context Camera, or CTX, or cameras on other orbiters. The new estimate of cratering rate is based on a portion of the 248 new craters detected. If comes from a systematic check of a dusty fraction of the planet with CTX since late 2006.
The impacts disturb the dust, creating noticeable blast zones. In this part of the research, 44 fresh impact sites were identified. The meteor over Chelyabinsk, Russia, in February was about 10 times bigger than the objects that dug the fresh Martian craters. Estimates of the rate at which new craters appear serve as scientists' best yardstick for estimating the ages of exposed landscape surfaces on Mars and other worlds.
Daubar and co-authors calculated a rate for how frequently new craters at least 12.8 feet (3.9 meters) in diameter are excavated. The rate is equivalent to an average of one each year on each area of the Martian surface roughly the size of the U.S. state of Texas. Earlier estimates pegged the cratering rate at three to 10 times more craters per year. They were based on studies of craters on the moon and the ages of lunar rocks collected during NASA's Apollo missions in the late 1960s and early 1970s.
"Mars now has the best-known current rate of cratering in the solar system," said UA's HiRISE Principal Investigator Alfred McEwen, a co-author on the paper.
MRO has been examining Mars with six instruments since 2006. Daubar is an imaging targeting specialist who has been on the HiRISE uplink operation s team from the very beginning. She is also a graduate student in the UA's department of planetary science and plans on graduating with her doctorate in spring 2014.
"There are five of us who help plan the images that HiRISE will take over a two-week cycle," she explained. "We work with science team members across the world to understand their science goals, help select the image targets and compile the commands for the spacecraft and the camera."
"The longevity of this mission is providing wonderful opportunities for investigating changes on Mars," said MRO Deputy Project Scientist Leslie Tamppari of NASA's Jet Propulsion Laboratory in Pasadena, Calif. | 0.884583 | 3.91405 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2013 August 15
Explanation: In an astronomical version of the search for the source of the Nile, astronomers now have strong evidence for the origin of the Magellanic Stream. This composite image shows the long ribbon of gas, discovered at radio wavelengths in the 1970s, in pinkish hues against an optical all-sky view across the plane of our Milky Way galaxy. Both Large and Small Magellanic Clouds, dwarf satellite galaxies of the the Milky Way, are seen near the head of the stream at the right. Data from Hubble's Cosmic Origins Spectrograph were used to explore abundances of elements along sightlines to quasars that intersect the stream. The results indicate that most of the stream's material comes from the Small Magellanic Cloud. The Magellanic Stream is likely the result of gravitational tidal interactions between the two dwarf galaxies some 2 billion years ago, the Small Magellanic Cloud losing more material in the encounter because of its lower mass.
Authors & editors:
Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
A service of: ASD at NASA / GSFC
& Michigan Tech. U. | 0.890953 | 3.188222 |
Experimental study of gravitation
The essence of Newton’s theory of gravitation is that the force between two bodies is proportional to the product of their masses and the inverse square of their separation and that the force depends on nothing else. With a small modification, the same is true in general relativity. Newton himself tested his assumptions by experiment and observation. He made pendulum experiments to confirm the principle of equivalence and checked the inverse square law as applied to the periods and diameters of the orbits of the satellites of Jupiter and Saturn.
During the latter part of the 19th century, many experiments showed the force of gravity to be independent of temperature, electromagnetic fields, shielding by other matter, orientation of crystal axes, and other factors. The revival of such experiments during the 1970s was the result of theoretical attempts to relate gravitation to other forces of nature by showing that general relativity was an incomplete description of gravity. New experiments on the equivalence principle were performed, and experimental tests of the inverse square law were made both in the laboratory and in the field.
There also has been a continuing interest in the determination of the constant of gravitation, although it must be pointed out that G occupies a rather anomalous position among the other constants of physics. In the first place, the mass M of any celestial object cannot be determined independently of the gravitational attraction that it exerts. Thus, the combination GM, not the separate value of M, is the only meaningful property of a star, planet, or galaxy. Second, according to general relativity and the principle of equivalence, G does not depend on material properties but is in a sense a geometric factor. Hence, the determination of the constant of gravitation does not seem as essential as the measurement of quantities like the electronic charge or Planck’s constant. It is also much less well determined experimentally than any of the other constants of physics.
Experiments on gravitation are in fact very difficult, as a comparison of experiments on the inverse square law of electrostatics with those on gravitation will show. The electrostatic law has been established to within one part in 1016 by using the fact that the field inside a closed conductor is zero when the inverse square law holds. Experiments with very sensitive electronic devices have failed to detect any residual fields in such a closed cavity. Gravitational forces have to be detected by mechanical means, most often the torsion balance, and, although the sensitivities of mechanical devices have been greatly improved, they are still far below those of electronic detectors. Mechanical arrangements also preclude the use of a complete gravitational enclosure. Last, extraneous disturbances are relatively large because gravitational forces are very small (something that Newton first pointed out). Thus, the inverse square law is established over laboratory distances to no better than one part in 104.
The inverse square law
Recent interest in the inverse square law arose from two suggestions. First, the gravitational field itself might have a mass, in which case the constant of gravitation would change in an exponential manner from one value for small distances to a different one for large distances over a characteristic distance related to the mass of the field. Second, the observed field might be the superposition of two or more fields of different origin and different strengths, one of which might depend on chemical or nuclear constitution. Deviations from the inverse square law have been sought in three ways:
- The law has been checked in the laboratory over distances up to about 1 metre.
- The effective value of G for distances between 100 metres and 1 km has been estimated from geophysical studies.
- There have been careful comparisons of the value of the attraction of Earth as measured on the surface and as experienced by artificial satellites.
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Early in the 1970s an experiment by the American physicist Daniel R. Long seemed to show a deviation from the inverse square law at a range of about 0.1 metre. Long compared the maximum attractions of two rings upon a test mass hung from the arm of a torsion balance. The maximum attraction of a ring occurs at a particular point on the axis and is determined by the mass and dimensions of the ring. If the ring is moved until the force on the test mass is greatest, the distance between the test mass and the ring is not needed. Two later experiments over the same range showed no deviation from the inverse square law. In one, conducted by the American physicist Riley Newman and his colleagues, a test mass hung on a torsion balance was moved around in a long hollow cylinder. The cylinder approximates a complete gravitational enclosure and, allowing for a small correction because it is open at the ends, the force on the test mass should not depend on its location within the cylinder. No deviation from the inverse square law was found. In the other experiment, performed in Cambridge, Eng., by Y.T. Chen and associates, the attractions of two solid cylinders of different mass were balanced against a third cylinder so that only the separations of the cylinders had to be known; it was not necessary to know the distances of any from a test mass. Again no deviation of more than one part in 104 from the inverse square law was found. Other, somewhat less-sensitive experiments at ranges up to one metre or so also have failed to establish any greater deviation.
The geophysical tests go back to a method for the determination of the constant of gravitation that had been used in the 19th century, especially by the British astronomer Sir George Airy. Suppose the value of gravity g is measured at the top and bottom of a horizontal slab of rock of thickness t and density d. The values for the top and bottom will be different for two reasons. First, the top of the slab is t farther from the centre of Earth, and so the measured value of gravity will be less by 2(t/R)g, where R is the radius of Earth. Second, the slab itself attracts objects above and below it toward its centre; the difference between the downward and upward attractions of the slab is 4πGtd. Thus, a value of G may be estimated. Frank D. Stacey and his colleagues in Australia made such measurements at the top and bottom of deep mine shafts and claimed that there may be a real difference between their value of G and the best value from laboratory experiments. The difficulties lie in obtaining reliable samples of the density and in taking account of varying densities at greater depths. Similar uncertainties appear to have afflicted measurements in a deep bore hole in the Greenland ice sheet.
New measurements have failed to detect any deviation from the inverse square law. The most thorough investigation was carried out from a high tower in Colorado. Measurements were made with a gravimeter at different heights and coupled with an extensive survey of gravity around the base of the tower. Any variations of gravity over the surface that would give rise to variations up the height of the tower were estimated with great care. Allowance was also made for deflections of the tower and for the accelerations of its motions. The final result was that no deviation from the inverse square law could be found.
A further test of the inverse square law depends on the theorem that the divergence of the gravity vector should vanish in a space that is free of additional gravitational sources. An experiment to test this was performed by M.V. Moody and H.J. Paik in California with a three-axis superconducting gravity gradiometer that measured the gradients of gravity in three perpendicular directions. The sum of the three gradients was zero within the accuracy of the measurements, about one part in 104.
The absolute measurements of gravity described earlier, together with the comprehensive gravity surveys made over the surface of Earth, allow the mean value of gravity over Earth to be estimated to about one part in 106. The techniques of space research also have given the mean value of the radius of Earth and the distances of artificial satellites to the same precision. Thus, it has been possible to compare the value of gravity on Earth with that acting on an artificial satellite. Agreement to about one part in 106 shows that, over distances from the surface of Earth to close satellite orbits, the inverse square law is followed.
Thus far, all of the most reliable experiments and observations reveal no deviation from the inverse square law.
The principle of equivalence
Experiments with ordinary pendulums test the principle of equivalence to no better than about one part in 105. Eötvös obtained much better discrimination with a torsion balance. His tests depended on comparing gravitational forces with inertial forces for masses of different composition. Eötvös set up a torsion balance to compare, for each of two masses, the gravitational attraction of Earth with the inertial forces due to the rotation of Earth about its polar axis. His arrangement of the masses was not optimal, and he did not have the sensitive electronic means of control and reading that are now available. Nonetheless, Eötvös found that the weak equivalence principle (see above Gravitational fields and the theory of general relativity) was satisfied to within one part in 109 for a number of very different chemicals, some of which were quite exotic. His results were later confirmed by the Hungarian physicist János Renner. Renner’s work has been analyzed recently in great detail because of the suggestion that it could provide evidence for a new force. It seems that the uncertainties of the experiments hardly allow such analyses.
Eötvös also suggested that the attraction of the Sun upon test masses could be compared with the inertial forces of Earth’s orbital motion about the Sun. He performed some experiments, verifying equivalence with an accuracy similar to that which he had obtained with his terrestrial experiments. The solar scheme has substantial experimental advantages, and the American physicist Robert H. Dicke and his colleagues, in a careful series of observations in the 1960s (employing up-to-date methods of servo control and observation), found that the weak equivalence principle held to about one part in 1011 for the attraction of the Sun on gold and aluminum. A later experiment by the Russian researcher Vladimir Braginski, with very different experimental arrangements, gave a limit of about one part in 1012 for platinum and aluminum.
Galileo’s supposed experiment of dropping objects from the Leaning Tower of Pisa has been reproduced in the laboratory with apparatuses used to determine the absolute value of gravity by timing a falling body. Two objects, one of uranium, the other of copper, were timed as they fell. No difference was detected.
Laser-ranging observations of the Moon in the LAGEOS (laser geodynamic satellites) experiment have also failed to detect deviations from the principle of equivalence. Earth and the Moon have different compositions, the Moon lacking the iron found in Earth’s core. Thus, if the principle of equivalence were not valid, the accelerations of Earth and the Moon toward the Sun might be different. The very precise measurements of the motion of the Moon relative to Earth could detect no such difference.
By the start of the 21st century, all observations and experiments on gravitation had detected that there are no deviations from the deductions of general relativity, that the weak principle of equivalence is valid, and that the inverse square law holds over distances from a few centimetres to thousands of kilometres. Coupled with observations of electromagnetic signals passing close to the Sun and of images formed by gravitational lenses, those observations and experiments make it very clear that general relativity provides the only acceptable description of gravitation at the present time.
The constant of gravitation
The constant of gravitation has been measured in three ways:
- The comparison of the pull of a large natural mass with that of Earth
- The measurement with a laboratory balance of the attraction of Earth upon a test mass
- The direct measurement of the force between two masses in the laboratory
The first approach was suggested by Newton; the earliest observations were made in 1774 by the British astronomer Nevil Maskelyne on the mountain of Schiehallion in Scotland. The subsequent work of Airy and more-recent developments are noted above. The laboratory balance method was developed in large part by the British physicist John Henry Poynting during the late 1800s, but all the most recent work has involved the use of the torsion balance in some form or other for the direct laboratory measurement of the force between two bodies. The torsion balance was devised by Michell, who died before he could use it to measure G. Cavendish adapted Michell’s design to make the first reliable measurement of G in 1798; only in comparatively recent times have clearly better results been obtained. Cavendish measured the change in deflection of the balance when attracting masses were moved from one side to the other of the torsion beam. The method of deflection was analyzed most thoroughly in the late 1800s by Sir Charles Vernon Boys, an English physicist, who carried it to its highest development, using a delicate suspension fibre of fused silica for the pendulum. In a variant of that method, the deflection of the balance is maintained constant by a servo control.
The second scheme involves the changes in the period of oscillation of a torsion balance when attracting masses are placed close to it such that the period is shortened in one position and lengthened in another. Measurements of period can be made much more precisely than those of deflection, and the method, introduced by Carl Braun of Austria in 1897, has been used in many subsequent determinations. In a third scheme the acceleration of the suspended masses is measured as they are moved relative to the large attracting masses.
In another arrangement a balance with heavy attracting masses is set up near a free test balance and adjusted so that it oscillates with the same period as the test balance. The latter is then driven into resonant oscillations with an amplitude that is a measure of the constant of gravitation. The technique was first employed by J. Zahradnicek of Czechoslovakia during the 1930s and was effectively used again by C. Pontikis of France some 40 years later.
Suspensions for two-arm balances for the comparison of masses and for torsion balances have been studied intensively by T.J. Quinn and his colleagues at the International Bureau of Weights and Measures, near Paris, and they have found that suspensions with thin ribbons of metal rather than wires provide the most stable systems. They have used balances with such suspensions to look for deviations from the predictions of general relativity and have most recently used a torsion balance with ribbon suspension in two new determinations of the constant of gravitation.
Many new determinations of G were made in the five years from 1996 to 2001. However, despite the great attention given to systematic errors in those experiments, it is clear from the range of the results that serious discrepancies, much greater than the apparent random errors, still afflict determinations of G. In 2001 the best estimate of G was taken to be 6.67553 × 10−11 m3 s−2 kg−1. Results before 1982 indicate a lower value, perhaps 6.670, but those from 1996 onward suggest a higher value.
Values of the constant of gravitation
|H. Cavendish ||1798 ||torsion balance (deflection) ||6.754 |
|J.H. Poynting ||1891 ||common balance ||6.698 |
|C.V. Boys ||1895 ||torsion balance (deflection) ||6.658 |
|C. Braun ||1897 ||torsion balance (deflection) ||6.658 |
|C. Braun ||1897 ||torsion balance (period) ||6.658 |
|P.R. Heyl ||1930 ||torsion balance (period) ||6.669 |
|J. Zahradnicek ||1932 ||torsion balance (resonance) ||6.659 |
|P.R. Heyl, P. Chrzanowski ||1942 ||torsion balance (period) ||6.672 |
|C. Pontikis ||1972 ||torsion balance (resonance) ||6.6714 |
|G.G. Luther and W.R. Towler ||1982 ||torsion balance (period) ||6.6726 |
|H. de Boer ||1987 ||mercury flotation (deflection) ||6.667 |
|W. Michaelis et al. ||1996 ||flotation (null deflection) ||6.7164 |
|C.H. Bagley and G.G. Luther ||1997 ||torsion balance (period) ||6.6740 |
|O.V. Karagioz et al. ||1998 ||torsion balance (period) ||6.6729 |
|J. Luo et al. ||1999 ||torsion balance (period) ||6.6699 |
|M.P. Fitzgerald, T.R. Armstrong ||1999 ||torsion balance (null deflection) ||6.6742 |
|F. Nolting et al. ||1999 ||common balance ||6.6754 |
|U. Kleinvoss et al. ||1999 ||pendulum deflection ||6.6735 |
|J.H. Gundlach, S.M. Merkowitz ||2000 ||torsion balance (acceleration) ||6.67422 |
|T.J. Quinn et al. ||2001 ||torsion balance (servo) ||6.67553 |
|T.J. Quinn et al. ||2001 ||torsion balance (deflection) ||6.67565 |
The variation of the constant of gravitation with time
The 20th-century English physicist P.A.M. Dirac, among others, suggested that the value of the constant of gravitation might be proportional to the age of the universe; other rates of change over time also have been proposed. The rates of change would be extremely small, one part in 1011 per year if the age of the universe is taken to be 1011 years; such a rate is entirely beyond experimental capabilities at present. There is, however, the possibility of looking for the effects of any variation upon the orbit of a celestial body, in particular the Moon. It has been claimed from time to time that such effects may have been detected. As yet, there is no certainty.
Fundamental character of G
The constant of gravitation is plainly a fundamental quantity, since it appears to determine the large-scale structure of the entire universe. Gravity is a fundamental quantity whether it is an essentially geometric parameter, as in general relativity, or the strength of a field, as in one aspect of a more-general field of unified forces. The fact that, so far as is known, gravitation depends on no other physical factors makes it likely that the value of G reflects a basic restriction on the possibilities of physical measurement, just as special relativity is a consequence of the fact that, beyond the shortest distances, it is impossible to make separate measurements of length and time. | 0.809748 | 3.876769 |
Space transport to benefit from propulsion systems based on fusion plasma
A Soyuz rocket sitting on the launchpad holds approximately 347,000 pounds of propellant in each of its four boosters. While this is great for thrusting the craft into orbit, it comes at a heavy price – literally. But what if we could reduce the amount of fuel needed?
Researchers from the Institute of Space Systems (IRS) at the University of Stuttgart, Germany, have been studying a possible propulsion system for space transport, based on an approach referred to as inertial electrostatic confinement (IEC) of plasma sources. This uses an electric field to heat plasma to fusion conditions. The team chose to investigate the phenomena in an IEC device that leads to jet extraction, finding that it could produce ion jets with very high kinetic energy. Their results are published in the journal Vacuum.
Georg Herdrich, deputy head of the Department of Space Transportation at IRS, explains: "Our IRS system produces a jet that can be used in a future advanced electric space propulsion system, saving significant amounts of propellant mass due to its high kinetic energy. Moreover, the system may also be used as an air breathing propulsion system in Earth's thermosphere, giving very low flying satellite systems an increased lifetime as the propulsion system compensates the satellite’s drag.”
Both electric space propulsion systems and air breathing propulsion systems have the ability to reduce the mass of propellant necessary to propel rockets into space. Electric propulsion systems, currently used in Russian satellites, electrically expel propellant at a high speed, thus using less propellant than a chemical rocket. Air breathing systems make use of atmospheric oxygen to burn fuel onboard making the system lighter, more efficient and cost effective. This type of system could be used in the follow-up mission to the Gravity Field and Steady State Ocean Circulation Explorer (GOCE), which intends to map the Earth's gravity field.
The IRS team systematically assessed the jet production from the IEC device and the preliminary characteristics of its discharge using emission spectroscopy. "Taking the IEC’s jet as a point of departure for a future space propulsion system, our first analyses imply that its ion energies are significantly higher than classical ion thrusters," says Herdich.
He adds: “We are testing a thruster prototype in collaboration with industry. Our promising data confirm our well-educated guesses about the jet characteristics and our interpretation enables a variety of new applications. This is interesting, because of the very significant impact a readily developed IEC-based electric space propulsion system would have for a variety of space applications.”
The researchers hope that electric space propulsion systems will take spacecraft to the outer solar system. Perhaps, it will one day enable interstellar flight.
Syring, C. and Herdich, G.: "Jet extraction modes of inertial electrostatic confinement devices for electric propulsion applications", Vacuum (2017). | 0.843486 | 3.317045 |
Using one of the world's largest telescopes, a Lawrence Livermore team and international collaborators have tracked the orbit of a planet at least four times the size of Jupiter.
The scientists were able to identify the orbit of the exoplanet, Beta Pictoris b, which sits 63 light years from our solar system, by using the Gemini Planet Imager's (GPI) next-generation, high-contrast adaptive optics (AO) system. This approach is sometimes referred to as extreme AO.
Lawrence Livermore researchers and international collaborators have refined estimates of the orbit and size of the exoplanet Beta Pictoris b.
The Gemini Planet Imager captured this first light image of Beta Pictoris b, a planet orbiting the star Beta Pictoris. The star, Beta Pictoris, is blocked in this image by a mask so its light doesn't interfere with the light of the planet.
The Gemini Planet Imager snapped an amazingly clear and bright image of the gas giant Beta Pictoris b after an exposure of just one minute.
By using a series of these images and calibrating the AO system and camera, researchers were able to refine the estimate of the planet's orbit by looking at the two disks around its parent star. Disks, which are made up of dense gas and debris, surround young newly formed stars. The team observed that the planet is not aligned with Beta Pictoris' (its star's) main debris disk but is aligned to and potentially interacting with an inner warped component disk.
"Our goal is to understand how these planetary systems have developed," said Lisa Poyneer, one of the lead Lawrence Livermore authors of a paper appearing in a recent edition of the journal, Proceedings of the National Academy of Sciences. "If Beta Pictoris b is warping the disk, that helps us see how the planet-forming disk in our own solar system might have evolved long ago."
Furthermore, the team predicts that there is a small chance that the planet will "transit," that is, partially block its star, as seen from Earth in late 2017. This would allow a very precise measurement of the planet's size. Poyneer concludes: "GPI also measures the planet's spectrum, and hence chemical composition. Knowing what it is made of and how big it is will help us figure out how it formed."
For the past decade, Lawrence Livermore has been leading a multi-institutional team in the design, engineering, building and optimization of GPI, which is used for high-contrast imaging to better study faint planets or dusty disks next to bright stars. Astronomers -- including a team at LLNL-- have made direct images of a handful of extrasolar planets by adapting astronomical cameras built for other purposes. GPI is the first fully optimized planet imager, designed from the ground up for exoplanet imaging and deployed on one of the world's biggest telescopes, the 8-meter Gemini South telescope in Chile.
Poyneer said the team is assessing how the AO system is performing and making adjustments as necessary so that it can image even more exoplanets. "The system is functioning very well and enabling new science already, but we're further improving its performance," she said.
Other Livermore scientists include Bruce Macintosh, now at Stanford University, Brian Bauman and David Palmer. The research appears in the May 12 online edition of PNAS.
Anne Stark | Eurek Alert!
Hope to discover sure signs of life on Mars? New research says look for the element vanadium
22.09.2017 | University of Kansas
22.09.2017 | Forschungszentrum MATHEON ECMath
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
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22.09.2017 | Physics and Astronomy | 0.902576 | 3.952002 |
Earth's Invisible Magnetic Tail
The first global views of our planet's magnetosphere,
captured by NASA's IMAGE spacecraft, reveal a curious plasma
tail that stretches toward the Sun.
January 25, 2001 -- The first large-scale pictures of the hidden machinations of the Earth's magnetic force-field are now available, including confirmation of a suspected but previously invisible "tail" of electrified gas.
The tail, which streams from Earth towards the Sun, was spotted by NASA's Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft. It's featured on the cover of the Jan. 26 issue of the journal Science. IMAGE is offering researchers an unprecedented view of the transparent, electrified gas trapped within Earth's magnetic field, providing the first visual, global perspective on magnetic storms.
Right: The Extreme Ultraviolet imager (EUV) instrument on board IMAGE captured this picture of the ultraviolet glow from relatively cold plasma surrounding our planet. A hook-shaped "tail" of plasma, near the top-left, streams toward the Sun. The small, faint circle near the center of the image traces ultraviolet radiation from aurora borealis (or "Northern Lights"). [more]
The region laced by Earth's magnetic field, called the magnetosphere, dominates the behavior of electrically charged particles in space near Earth and shields our planet from the solar wind. Explosive events on the Sun can charge the magnetosphere with energy, generating magnetic storms that occasionally affect satellites, communications and power systems.
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"Imagine trying to track and understand the formation of hurricanes without the view from weather satellites," said Dr. Thomas Moore, IMAGE Project Scientist at NASA's Goddard Space Flight Center. "Like the first meteorologists with a small number of measuring stations, we had an incomplete and at times misleading view of the magnetosphere before IMAGE, because we couldn't see the big picture."
"IMAGE is providing for the first time global views of the Earth's charged-particle populations at multiple wavelengths and energies on time scales of a few minutes, which is sufficient to track the dynamics of the magnetosphere," said Dr. James Burch, IMAGE Principal Investigator and lead author of the Science paper at Southwest Research Institute.
The Earth's magnetosphere traps electrified gas, called plasma. The new IMAGE pictures show a tail-like structure in the Earth's own plasma cloud that forms as some of the gas streams toward the Sun. The structure was predicted 30 years ago, but previous spacecraft were unable to confirm its existence.
The tail structure is believed to be a return flow of plasma that occurs when the solar wind buffets the magnetosphere and distorts its shape. For example, a falling raindrop is at first roughly spherical. As it falls and gains speed, air resistance causes the droplet to change shape as water is dragged from the bottom (head) to the top (tail). Surface tension prevents most of the water from simply dispersing from the tail, so it is forced instead to flow within the raindrop and return to the head.
The solar wind distorts the Earth's magnetosphere in a similar way, compressing it on the Earth's day side, like the head of a raindrop. The region is stretched on the night side, like the raindrop's tail, forming a teardrop shape.
Plasma near the boundaries of the magnetosphere is dragged with the solar wind, but then is turned around and forced back towards the Sun. Although the Sun-pointing plasma tail was expected, IMAGE uncovered some surprises too. For one thing, the spacecraft discovered areas in Earth's plasma cloud that are nearly empty of plasma. The IMAGE team calls these unexpected structures "troughs" and is trying to discover how they form.
IMAGE, launched March 25, 2000, also revealed some surprising activity during magnetic storms, which occur when the solar wind pummels the Earth's magnetosphere. The night-side region of the magnetosphere, which is stretched out by the solar wind, sometimes snaps back and shoots plasma violently toward Earth. The plasma becomes heated to several hundred million degrees and whirls around Earth in multi-million-amp currents. IMAGE discovered that such plasma occasionally is most dense on the Earth's day side, which was unexpected. Researchers are currently studying the phenomenon.
Above: IMAGE's High Energy Neutral Atom (HENA) instrument
captured this false color image of neutral atoms glowing inside
the hot plasma surrounding Earth. Orange-white denotes the most
dense plasma, while red traces the least dense. The hot plasma
in this image is densest on Earth's day side, which was unexpected.
TRICK O' THE TAIL: IMAGE SATELLITE SEES EARTH'S INVISIBLE MAGNETIC REALM -- Goddard's online press release about the latest IMAGE results includes plenty of related links.
IMAGE home page -- at the NASA Goddard Space Flight Center
From the Drawing Board to the Stars -- Science@NASA article: Dr. Jim Burch, principal investigator for NASA's IMAGE space weather satellite, describes what its like to first imagine a space mission and then make it happen.
The RADAR Cop in Space -- Science@NASA article: NASA's IMAGE satellite will revolutionize our understanding of Earth's magnetosphere and improve space weather forecasting.
Space Weather Satellite Blasts Off -- Science@NASA article: NASA's IMAGE satellite successfully flies into orbit from Vandenberg AFB.
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Dark matter is kind of old-hat in these exciting days of dark energy. Nevertheless, we don't know very much about it. We know that it exists, we have a very good idea of where it is, and we even know how much of it is around—but we don't know what it is or how it interacts with other matter aside from via gravity. These are now central questions for those who study dark matter, but they are also expected to be a short-lived ones. We can expect some pretty good answers in the next ten years as the LHC begins to build up a large database of collisions and data comes in from many cosmological observations that are already in progress.
The cosmological observations are already raising eyebrows and causing theorists to sharpen their pencils, though. All of these observations find significantly more electrons and positrons than expected coming from the galactic center. Now, in a very cool piece of physics, researchers have shown that all of these observations can be explained by dark matter interacting with itself.
First, lets take a look at the observational data, starting with the cosmic microwave background radiation. The current map, produced by WMAP, shows a haze of hard radiation around the galactic center. It turns out that the data is best explained by synchrotron radiation, produced by charged particles going around in circles near the galactic center. But that implies that there are more charged particles out there than we'd expect.
Then there is the data obtained by PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics). The scientists in charge have found that there are many more high-energy electrons and positrons than can be accounted for by the interaction of high-energy cosmic rays with the interstellar medium—they have already accounted for all other known sources in order to study cosmic rays in the first place. Similar results have been found by other cosmic ray observatories, and by gamma ray observatories as well.
There are other observations that seem to display the same sort of anomaly but—and here is the kicker—all of these experiments are observing different physical phenomena in different ways, yet reporting the same problematic result. To add to cosmologists' problems, the conflicting results have been obtained by the LIBRA/DAMA collaboration and their competitors. LIBRA/DAMA claims to have observed an annual modulation in dark matter collisional interactions, a result they ascribe to the Earth traveling with and against galactic rotation as it circles the sun. Similar experiments run by other groups have failed to find such a signal, and the contradictory results have, frankly, confused everyone.
To make matters worse, every single observation could be explained by assuming that something is unusual about that particular observation—for instance, supernovae could be blurring WMAP's vision. But this is pretty unsatisfactory, because the point of observation is to collect phenomena under an umbrella of a few descriptive and predictive models, rather than adding extra phenomena to explain each observation.
A group of scientists have taken the first steps toward attempting to unify these phenomena under a single theoretical umbrella. To do this, they have posited that the electrons and positrons are the result of dark matter annihilations, while other annihilation paths that lead to different particles are suppressed. This idea is not as obvious as it sounds, because the number and energies of the electrons and positrons indicate that dark matter must be pretty strongly interacting, and interacting is on the list of things dark matter doesn't do.
This problem can be alleviated if one assumes that there is relatively long-range force that acts between dark matter particles. This force can then enhance the probability that dark matter annihilates in a way that produces electrons and positrons while also suppressing other annihilation pathways. The nice thing is that this force provides an internal structure to dark matter that also explains why DAMA/LIBRA saw a dark matter annual modulation signal and other experiments did not. In other words, this single hypothesis brings a wide range of observations together and makes predictions about the properties of dark matter—everything you want in a hypothesis looking to make its way to theory status.
But, I hear you say, they have replaced a few special phenomena that we know exist with one force that we don't know exists—surely, that is a step backwards. Well, it is true that further examination may prove that some of the observations are the result of special circumstances. It is, however, unlikely that all of them are. Furthermore, we know that there are very likely to be other bosons out there, awaiting the LHC attempt to reveal their existence. It doesn't seem unreasonable to suppose that one of them has the mass required for a dark force carrier.
So, no, this isn't pure speculation, and, no, it doesn't rely on "something really strange emerging from the LHC." Nevertheless, it still requires a lot of confirmation before it gets its own chapter in physics text books.
Physical Review D, DOI: 10.1103/PhysRevD.79.015014 | 0.852721 | 4.146015 |
Ever since Neptune was discovered in 1846, astronomers have wondered about the possibility of the existence of another, far more distant planet in our solar system. Discrepancies in the orbits of the outer planets have even led some scientists to theorize about the existence of a "Planet X," a phantom planet with mass large enough to explain these gravitational deviations.
Now a new analysis of the orbits of our solar system's "extreme trans-Neptunian objects" or ETNOs — bodies that have been found to exist in the outskirts of our solar system — has revitalized the Planet X theory. In fact, scientists suspect there may be at least two more undiscovered planets in our solar system, planets larger than Earth but more distant than Pluto, reports NBC News.
"This excess of objects with unexpected orbital parameters makes us believe that some invisible forces are altering the distribution of the orbital elements of the ETNOs, and we consider that the most probable explanation is that other unknown planets exist beyond Neptune and Pluto," lead author Carlos de la Fuente Marcos, of the Complutense University of Madrid, said in a statement.
"The exact number is uncertain, given that the data that we have is limited, but our calculations suggest that there are at least two planets, and probably more, within the confines of our solar system," he added.
How is it possible that such large objects could remain undetected within our own solar system? Well, such planets would be so distant from the sun that they would be virtually undetectable with modern instruments. To put it in perspective, the distance from Earth to the sun is measured as 1 AU (astronomical units). Pluto, by comparison, is almost 50 AU at its furthest orbit. The distance between the proposed new planets and the sun would be a whopping 200 AU or more. That's four times the distance of Pluto from the sun at its furthest orbit! So it's unlikely that we'll be spying Planet X or Y anytime soon.
Even so, if the results are confirmed, they would represent one of the greatest astronomical discoveries in recent history. The research is published in the Monthly Notices of the Royal Astronomical Society.
Related on MNN: | 0.816548 | 3.425419 |
NASA is counting down to Friday's launch of Juno, just the second probe sent specifically to study Jupiter, on a mission that should see the spacecraft arrive at the solar system's largest planet in August 2016.
Among Juno's mission objectives will be the construction of a 3-D map of Jupiter's full environment, according to Space.com.
"Each of the missions that we do are providing unique and very important information," said Scott Bolton of the Southwest Research Institute in San Antonio, Juno's principal investigator, told reporters this week. "Some of those earlier missions were reconnaissance, so we could figure out what are the right questions, and they essentially led us to ask the questions that we have with Juno."
The spacecraft will actually swing by Earth two years after its launch in order to use our planet's gravity as a slingshot to boost its acceleration all the way to Jupiter.
Juno is set to join Galileo as the only spacecraft sent on a dedicated mission to orbit and study Jupiter (see video below for a preview of the Juno mission). Galileo was launched in October 1989 and arrived in orbit around the gas giant in December 1995, where it dropped a probe into the Jupiter's atmosphere. After studying several Jovian satellites, Galileo was intentionally crashed into Jupiter in 2003 to prevent it from contaminating the planet's moons with terrestrial bacteria.
It is hoped that the Juno mission will add considerably to the information about Jupiter sent back by Galileo and other spacecraft passing by the planet, to "fill in the gaps in their understanding of Jupiter's formation and evolution, as well as the history of the solar system in general."
In addition to the 3D mapping project, Juno is equipped with advanced instrumentation that scientists will use to study Jupiter's atmosphere, magnetosphere, gravitational field, and violent polar auroras.
Space.com has a rundown of other spacecraft to visit Jupiter, though unlike Galileo and Juno, those probes only passed by the giant planet on their way to other destinations.
The other spacecraft that have visited Jupiter, if only briefly, include Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Ulysses, Cassini-Huygens, and New Horizons. | 0.852561 | 3.173224 |
If you're trying to get actual images of exoplanets, it helps to look at M-dwarfs, particularly young ones.
These stars, from a class that makes up perhaps 75 percent of all the stars in the galaxy, are low in mass and much dimmer than their heavier cousins, meaning the contrast between the star's light and that of orbiting planets is sharply reduced. Young M-dwarfs are particularly helpful, especially when they are close to Earth, because their planets will have formed recently, making them warmer and brighter than planets in older systems.
The trick, then, is to identify young M-dwarfs, and it's not always easy. Such a star produces a higher proportion of X-rays and ultraviolet light than older stars, but even X-ray surveys have found it difficult to detect the less energetic M-dwarfs, and in any case, X-ray surveys have studied only a small portion of the sky. Astronomers at UCLA now have hopes of using a comparative approach, working with the Galaxy Evolution Explorer satellite, which has scanned a large part of the sky in ultraviolet light. These data are compared to optical and infrared observations to identify young stars that fit the bill for possible exoplanet detection.
So far the results are good. Of the 24 candidates identified with these methods, 17 turn out to show signs of stellar immaturity. The stars may be too young and low in mass to show up in X-ray surveys, but the Galaxy Evolution Explorer data seem effective at finding M-dwarfs less than 100 million years old. We can hope to add, then, to the tiny number of exoplanets that have been directly imaged, a useful adjunct to existing observing methods. Direct imaging can help us with large planets in the outer reaches of their solar systems, planets that would thus far have eluded Doppler methods. That helps us flesh out our view of complete planetary systems.
And yes, WISE (Wide-field Infrared Survey Explorer) is in the hunt here as well, helping us identify candidates from the M-dwarf category that would make good imaging targets. WISE can find young, nearby stars that are still surrounded by planetary debris disks, a fertile hunting ground for new planetary imaging. Putting the tools together across the spectrum should make it possible to find close young planets whose properties should help us in our studies of solar system formation. And we can expect release of the first 105 days of WISE data later this month.
As to the Galaxy Evolution Explorer, it was launched back in 2003 with a mission to observe distant galaxies in ultraviolet light. Now operating in extended mission mode, GALEX has been conducting an ultraviolet all-sky survey intended to produce a map of galaxies in formation, helping us see how our own galaxy evolved. Turning its ultraviolet capabilities to the study of exoplanets in young solar systems gives us a new technique for finding imaging targets.
The paper is Rodriguez et al., "A New Method to Identify Nearby, Young, Low-Mass Stars," Astrophysical Journal Vol. 727, No. 2 (2011), p. 62 (abstract).
[Top image: Galaxy Evolution Explorer looks at Andromeda. The wisps of blue making up the galaxy's spiral arms are neighborhoods that harbor hot, young, massive stars. Meanwhile, the central orange-white ball reveals a congregation of cooler, old stars that formed long ago. Now scientists are using GALEX data to hunt for young, planet-bearing red dwarfs near the Sun. Credit: NASA/JPL-Caltech.]
This post originally appeared on Centauri Dreams. | 0.862046 | 4.047968 |
In class, we learned Kepler’s three laws of planetary motion, which describe how planets orbit around a star. The three laws are as follows:
- A planet orbits around its sun in an ellipses.
- A radius vector joining any planet to its sun sweeps out equal areas in equal lengths of time.
- The revolution of a planet squared is directly proportional to the length of the orbits semimajor axis cubed. (This can be mathematically expressed as T^2/a^3 equals a constant. This constant is the same for every planet in its solar system.)
Before the discovery of these laws, we assumed that the planets travelled around the sun in a circular motion. Retrograde motion, such as that of Mars and Mercury, was unexplainable under this mindset. Kepler not only gave us an explanation for this retrograde motion, but also provided a basis for Newton to derive his laws of gravity from.
The article I found, titled “Mercury Retrograde” via universetoday.com, explains retrograde motion using Mercury as a specific example. Like we learned in class, the article explains that retrograde motion is an illusion caused by the elliptical path of planets. During its farthest point from the sun, planets move the slowest. So while Earth passes up Mercury when it’s at its farthest point, it appears to be going backwards from our point of view, even though it isn’t.
I liked the article because it helped reinforce the laws of planetary motion that we learned in class. I also liked the article because it talked about how people who closely follow astrology believe that mercury’s retrograde motion has an emotional affect on human behavior. This belief apparently derives from a time when the geocentric model of our solar system was accepted, so I find it interesting that people still takes these beliefs into consideration even though the information it was founded on has long ago proven to be complete garbage.
The fifth conceptual objective, I can apply Kepler’s laws of planetary motion, has been recently discussed in class. In class, we primarily defined and explained Kepler’s three laws of planetary motion. These laws were eventually exercised by the class in the Lecture-Tutorial book. Kepler’s first law says that the orbit of a planet is an ellipse with the sun at one focus. Kepler’s second law says that the line joining a planet and the sun sweeps out equal amounts of area in equal intervals of time. Finally, Kepler’s third law states that the square of a planet’s period is proportional to the cube length of the orbits semi-major axis. This concept can be expressed mathematically with the equation: T^2/a^3=constant. That said constant is the same for all objects orbiting the sun. Multiple illustrations in the Lecture-Tutorial book allowed me to get a better understanding of these three laws and concepts involving planetary motion. The article I chose, “Living on the Trappist-1 Planets Would Be Very Strange”, discusses the differences that would exist when living on one of the seven planets compared to Earth. This article closely relates to the fifth conceptual objective. As opposed to Earth, those who were standing on a planet in the Trappist-1 system would be able to see all six of the other planets. Due to their close proximity and orbits. This article relates to the fifth conceptual objective because it discusses the orbital periods of these seven planets, much like Kepler’s laws that are accepted here. These laws are universal and can even be applied to a planetary system that is nearly 40 light years away. All seven of the known planets in this system orbit closer to their star than Mercury orbits the Sun. Even in this instance, Kepler’s laws can be applied. The article the mentions the reason these planets can still support life, “The reason these seven planetary siblings can fit into such tight orbits is because their parent star is an ultra-cool dwarf star. It’s about 2,000 times dimmer than the sun, and only slightly larger than the planet Jupiter”. The article then begins to mention that the planets would appear to be dim to a person visiting one of these planets, regardless of the close orbits. The planets in this system take almost no time at all to make one complete orbit around their star. The article then discusses what life would be like on these planets. Kepler’s laws of planetary motion ultimately paved the way for universally accepted laws that define any orbit. Before Kepler came along, astronomers attempted to understand how the planets move. As discussed in our fourth conceptual objective, the geocentric theory was believed to be the truth by many. Eventually, this belief was overtaken by Copernicus. The concept of heliocentrism simplified models of planetary motion, and made the motions more explainable. However, it did not carefully explain retrograde motion. The elliptical orbits of planets is said to be caused by our altered perspective here on Earth. Although planetary motion was better demonstrated, it wasn’t until Kepler came along that planetary motion was explained with accepted laws. Kepler made countless calculations in order to prove his laws of planetary motion. This article is very comparable to what we exercised and discussed in class. This article clarifies the concept of planetary motion as defined by Kepler and shows that these laws can be applied elsewhere. The universal laws that originated from Kepler that define planetary motion seem to be consistent with other planetary systems. It is amazing that a man with very little technology could come up with three widely accepted laws that still exist today. The article provides useful information of this concept, further explaining our fifth conceptual objective. The precise layout of this article allows the reader to fully understand the material and apply it to other, real-world situations. | 0.854251 | 3.712615 |
It’s no longer a question of if there is water on the Moon; now it is how much. Scientists using the Mini-SAR instrument on India’s Chandrayaan-1 spacecraft have detected water ice deposits near the moon’s north pole. Mini-SAR, a lightweight, synthetic aperture radar, found more than 40 small craters with water ice. The craters range in size from 2 to15 km (1 to 9 miles) in diameter. Although the total amount of ice depends on its thickness in each crater, it is estimated there could be at least 600 million metric tons of water ice.
“The emerging picture from the multiple measurements and resulting data of the instruments on lunar missions indicates that water creation, migration, deposition and retention are occurring on the moon,” said Paul Spudis, principal investigator of the Mini-SAR experiment at the Lunar and Planetary Institute in Houston. “The new discoveries show the moon is an even more interesting and attractive scientific, exploration and operational destination than people had previously thought.”
During the past year, the Mini-SAR mapped the moon’s permanently-shadowed polar craters that aren’t visible from Earth. The radar uses the polarization properties of reflected radio waves to characterize surface properties. Results from the mapping showed deposits having radar characteristics similar to ice.
“After analyzing the data, our science team determined a strong indication of water ice, a finding which will give future missions a new target to further explore and exploit,” said Jason Crusan, program executive for the Mini-RF Program for NASA’s Space Operations Mission Directorate in Washington.
The results are consistent with recent findings of other NASA instruments and add to the growing scientific understanding of the multiple forms of water found on the moon. Previously, the Moon Mineralogy Mapper discovered water molecules in the moon’s polar regions, while water vapor was detected by NASA’s Lunar Crater Observation and Sensing Satellite, or LCROSS.
Mini-SAR and Moon Mineralogy Mapper are two of 11 instruments on Chandrayaan-1. The Mini-SAR’s findings are being published in the journal Geophysical Research Letters. | 0.811 | 3.626626 |
This is an image of Pluto.
Click on image for full size
Image from: NASA
An Overview of Pluto's Atmosphere
It may seem hard to believe that Pluto could have an atmosphere because it is so cold at 39 AU, where Pluto resides, but it does. Because there are times when Pluto is closer to the sun than is Neptune (making it the 8th planet for roughly 20 years at a time), ices on Pluto's surface evaporate and form an atmosphere. It is continually produced and lost again as long as Pluto is inside Neptune's orbit.
The air is made mostly of nitrogen gas, just like that of the Earth and Saturn's moon Titan, with the addition of carbon monoxide (CO - what comes out of your car) and methane (CH4).
The atmosphere is also similar to that of Neptune's moon Triton.. On Triton there are seasons and motions within the atmosphere. Because Pluto has a heavier atmosphere than Triton, there may even be clouds, winds, and storms. However, seeing these clouds and winds on Pluto is difficult.
It is also possible that the presence of nearby Charon draws material escaping from Pluto's atmosphere to recondense on the surface of Charon, as suggested in this image. So this binary planet may exchange atmospheric molecules.
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Triton, by far the largest moon of Neptune, is slightly smaller than Earth's Moon. Triton has the coldest surface temperatures in our Solar System. Surprisingly, this frigid moon has an atmosphere, albeit...more
Of all the planets and moons in the solar system, Pluto and Charon are the two which resemble each other the most closely. They are almost the same size, and they are very close together. They are so...more
Pluto is a frigid ball of ice and rock that orbits far from the Sun on the frozen fringes of our Solar System. Considered a planet, though a rather odd one, from its discovery in 1930 until 2006, it was...more
Pluto is so far away, and has never been explored. Questions to answer about Pluto include the following: What are the geologic features of the surface. (pictures of the surface) If there are bare spots,...more
It may seem hard to believe that Pluto could have an atmosphere because it is so cold at 39 AU, where Pluto resides, but it does. Because there are times when Pluto is closer to the sun than is Neptune...more
No one knows whether or not Pluto has a magnetosphere. Scientists were very surprised to find that Jupiter's icy moon Ganymede had a magnetosphere because it is hard to explain how an icy body can develop...more
Pluto has // Call the moon count function defined in the document head print_moon_count('pluto'); known moons. Charon, the largest by far, was discovered in 1978 by the American astronomer James Christy....more | 0.812012 | 3.355904 |
Early Earth was not very hospitable when it came to jump starting life. In fact, new research shows that life on Earth may have come from out of this world.
Lawrence Livermore scientist Nir Goldman and University of Ontario Institute of Technology colleague Isaac Tamblyn (a former LLNL postdoc) found that icy comets that crashed into Earth millions of years ago could have produced life building organic compounds, including the building blocks of proteins and nucleobases pairs of DNA and RNA.
Comets contain a variety of simple molecules, such as water, ammonia, methanol and carbon dioxide, and an impact event with a planetary surface would provide an abundant supply of energy to drive chemical reactions.
"The flux of organic matter to Earth via comets and asteroids during periods of heavy bombardment may have been as high as 10 trillion kilograms per year, delivering up to several orders of magnitude greater mass of organics than what likely pre-existed on the planet," Goldman said.
Goldman's earlier work is based on computationally intensive models, which, in the past, could only capture 10-30 picoseconds of a comet impact event. However new simulations, developed on LLNL's supercomputers Rzcereal and Aztec, Goldman used much more computationally efficient models and was able to capture hundreds of picoseconds of the impacts—much closer to chemical equilibrium.
"As a result, we now observe very different and a wider array of hydrocarbon chemical products that, upon impact, could have created organic material that eventually led to life," Goldman said.
Comets can range in size from 1.6 kilometers up to 56 kilometers. Comets passing through the Earth's atmosphere are heated externally but remain cool internally. Upon impact with the planetary surface, a shock wave is generated due to the sudden compression. Shock waves can create sudden, intense pressures and temperatures, which could affect chemical reactions within a comet before it interacts with the ambient planetary environment. An oblique collision where an extraterrestrial icy body impacts a planetary atmosphere with a glancing blow could generate thermodynamic conditions conducive to organic synthesis. These processes could result in significant concentrations of organic species being delivered to Earth.
The team found that moderate shock pressures and temperatures (approximately 360,000 atmospheres of pressure and 4,600 degrees Fahrenheit) in a carbon-dioxide-rich ice mixture produced a number of nitrogen-containing heterocycles, which dissociate to form functionalized aromatic hydrocarbons upon expansion and cooling. These are thought to be prebiotic precursors to DNA and RNA base pairs.
In contrast, higher shock conditions (about 480,000 to 600,000 atmospheres of pressure and 6,200-8,180 degrees Fahrenheit) resulted in the synthesis of methane and formaldehyde, as well as some long-chain carbon molecules. These compounds are known to act as precursors to amino acids and complex organic synthesis. All shock compression simulations at these conditions have produced significant quantities of new, simple carbon-nitrogen bonded compounds upon expansion and cooling, which are known prebiotic precursors.
"Cometary impacts could result in the synthesis of prebiotic molecules without the need for other 'special' conditions, such as the presence of catalysts, UV radiation, or special pre-existing conditions on a planet," Goldman said. "This data is critical in understanding the role of impact events in the formation of life-building compounds both on early Earth and on other planets and in guiding future experimentation in these areas."
Editor's Note: This article was originally published by PHYS ORG, here, and is licenced as Public Domain under Creative Commons. See Creative Commons - Attribution Licence. | 0.882248 | 3.996177 |
Two new and powerful research tools are helping astronomers gain key insights needed to transform our understanding of important processes across the breadth of astrophysics. The Atacama Large Millimeter/submillimeter Array (ALMA), and the newly-expanded Karl G. Jansky Very Large Array (VLA) offer scientists vastly improved and unprecedented capabilities for frontier research.
The cutting-edge research enabled by these powerful telescope systems extends from unlocking the mysteries of star- and planet-formation processes in the Milky Way and nearby galaxies, to probing the emergence of the first stars and galaxies at the Universe's "cosmic dawn," and along the way helping scientists figure out where Earth's water came from.
A trio of scientists outlined recent accomplishments of ALMA and the Jansky VLA, both of which are in the "early science" phase of their development, as construction progresses toward their completion. The astronomers spoke to the American Association for the Advancement of Science annual meeting in Vancouver, British Columbia.
One exciting area where the two facilities are expected to unlock longstanding mysteries is the study of how new stars and planets form, in our own Milky Way Galaxy and in its nearby neighbors.
"These new 'eyes' will allow us to study, at unprecedented scales, the motion of gas and dust in the disks surrounding young stars, and put our theories of planet formation to the test," said David Wilner of the Harvard-Smithsonian Center for Astrophysics (CfA). In addition, he added, the new telescopes will help show the first stages of planet formation -- the growth of dust grains and pebbles in the disks -- as well as show the gravitational interactions between the disks and new planets embedded within them.
"The power of ALMA and the expanded VLA also will allow us to study many more young stars and solar systems -- probably thousands -- than we could before. This will help us understand the processes that produce the huge diversity we already see in extrasolar planetary systems," Wilner said.
One set of early ALMA observations, of a disk around a young star nearly 170 light-years from Earth, promises to shed light on a much closer question -- the origin of Earth's oceans. Scientists think much of our planet's water came from comets bombarding the young Earth, but aren't sure just how much.
The key clue has been the fact that our seawater contains a higher percentage of Deuterium, a heavy isotope of Hydrogen, than is found in the gas between stars in our Galaxy. That enrichment of Deuterium is thought to be caused by low-temperature chemical reactions in the cold outer regions of the disk surrounding the young sun -- the region from which comets arise. The new ALMA observations, however, show that, in a disk surrounding the young star TW Hydrae, Deuterium also is found in the warmer region closer to the star.
"With further studies like this, we are on the path to more precisely measuring the percentage of Earth's ocean water that might have come from comets," Wilner said. Wilner worked with Karin Oberg and Chunhua Qi, also of CfA, and Michiel Hogerhejde of Leiden Observatory in the Netherlands, on this research.
Looking beyond the Milky Way, Christine Wilson, from McMaster University, points out that ALMA and the expanded VLA will give astronomers the ability to carefully study star formation in widely-different types of galaxies, from the very faint to the extremely luminous and active ones.
"This will help us understand what regulates the rate at which stars form in galaxies," Wilson said. One result from the VLA, however, seems to add to the mystery about this. John Cannon, of Mcalester College, and his colleagues studied a very small star-forming galaxy and found that its mass is largely dark matter, rather than the gas usually thought of as the fuel for star formation. "Their sample of small, but star-forming, galaxies has low amounts of gas, and this is puzzling," Wilson explained.
The two new telescopes also will help extend the study of galaxy evolution and star formation back to the Universe's youth, 10 or 12 billion years ago.
"The Jansky VLA and ALMA are ideally suited to reveal important new facts about very distant galaxies, which we see as they were when the Universe was a fraction of its current age," said Kartik Sheth, of the National Radio Astronomy Observatory. "The new capabilities of these two facilities will show us the details of dust and gas in galaxies of this early epoch, thus helping us learn how such galaxies evolved into the types we see in the current Universe," he added.
Already, Sheth said, both instruments have provided tantalizing glimpses of both atomic and molecular gas in galaxies as distant as 12 billion light-years.
"The huge range of ages in galaxies that we will be able to observe with these facilities represents a big step in piecing together the full history of how galaxies formed, evolved, and made stars, over the vast span of cosmic time," Sheth explained.
"The early research results from ALMA and the Jansky VLA show the tremendous potential of these facilities for studies of galaxies and their history. However, this is just one area of research in which these telescopes will make landmark contributions to our understanding of astronomical processes. ALMA and the Jansky VLA are leading tools for answering the most important questions of 21st-Century astrophysics," said National Radio Astronomy Observatory Director Fred K.Y. Lo.
ALMA is an international partnership of Europe, Japan, and North America in cooperation with the Republic of Chile, where the array is located at 5000 meters' elevation in the northern Andes. Located on the San Agustin Plains of central New Mexico, the Jansky VLA is a North American partnership, with the U.S. National Radio Astronomy Observatory and the National Science Foundation as the lead partner, and additional key contributions provided by the National Research Council in Canada, and the Consejo Nacional de Ciencia Tecnologia in Mexico.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. | 0.874793 | 3.969369 |
Study Reveals Our Milky Way Galaxy Contains A Massive Amount of Black Holes
Black holes are surprisingly common.
A new study has revealed that there are actually tens of millions of black holes in our own galaxy alone.
Few cosmic phenomena remain as frightening and mysterious as black holes – regions of space in which the gravitational pull is so great that nothing, not even light itself, can escape.
Exactly how many of them are out there has long remained a topic of debate among scientists, but now, by putting together a veritable cosmic inventory of stellar-remnant black holes, astronomers from the University of California, Irvine have determined that the universe appears to be teeming with them.
Even our own galaxy, the Milky Way, is thought to be home to as many as 100 million black holes.
The team’s celestial census began over 18 months ago, just after the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves for the first time.
“Fundamentally, the detection of gravitational waves was a huge deal, as it was a confirmation of a key prediction of Einstein’s general theory of relativity,” said co-author James Bullock.
“But then we looked closer at the astrophysics of the actual result, a merger of two 30-solar-mass black holes. That was simply astounding and had us asking, ‘How common are black holes of this size, and how often do they merge ?'”
Image Credit: NASA / Alain Riazuelo | 0.885631 | 3.362446 |
Solar astronomy is the study of our sun, which can also be called stellar astronomy because our sun is technically a star. The main branch of solar astronomy is solar physics, which is a branch of astrophysics that specifically studies the sun. The sun is our closest star, therefore is an ideal star to study and especially since changes in the sun’s atmosphere and activity can dramatically affect us here on earth. The sun has been studied for many centuries and along with the moon, ancient civilizations used the sun to help construct their calendars.
Study of the sun
Modern astronomers use special telescopes (in the past they used Heliographs) to detect light with wavelengths in the visible spectrum that can be detected by the human eye. These telescopes are operated during the day, which can cause turbulence from the ground being heated around the telescope. So, generally these telescopes are built on towers which are then painted white.
Discoveries made over the years
Some historical discoveries resulting in the study of solar astronomy include sunspot observations that could demonstrate the rotation of the sun, solar flares (which are a burst of energy deriving from the sun), solar radio waves, solar x-rays, solar wind (which is the never-ending stream of particles the sun constantly releases) and the discovery that the sun is made of hydrogen, not iron.
The benefits of solar astronomy compared to night astronomy is that you can observe during the day, you don’t need a huge telescope and the sun is constantly changing – it’s appearance won’t be the same tomorrow as it is today. | 0.821664 | 3.088859 |
It’s taken eight years to build, boasts 570 megapixels and it’s hoped that it’ll help answer one of the greatest mysteries in science – why the expansion of the universe is accelerating.
The Dark Energy Camera has come online on a mountaintop in Chile and produced its first incredible images.
The purpose of the camera, as its name suggests, is to hunt for dark energy.
Zoomed-in image from the Dark Energy Camera of the barred spiral galaxy NGC 1365, in the Fornax cluster of galaxies, which lies about 60 million light years from Earth
No one knows what the nature of that energy is – or even if it exists – but some experts believe that this hypothetical cosmic force is responsible for pushing the universe apart.
The camera, which was built at the US Department of Energy's (DOE) Fermi National Accelerator Laboratory in Batavia, Illinois, can see light from over 100,000 galaxies up to eight billion light years away – and it’s hope that this light will reveal why expansion of the universe is gaining speed.
"The achievement of first light through the Dark Energy Camera begins a significant new era in our exploration of the Cosmic Frontier," said James Siegrist, DOE associate director of science for high-energy physics.
This picture shows the Dark Energy Camera imager - the blue circle, left of centre
"The results of this survey will bring us closer to understanding the mystery of dark energy and what it means for the universe."
The Dark Energy Camera, which is about the size of a phone booth and is mounted on the Victor M Blanco telescope at the National Science Foundation's Cerro Tololo Inter-American Observatory, will also allow scientists from around the world to pursue investigations of asteroids in our own solar system.
But its primary purpose will be to carry out a Dark Energy Survey, the largest galaxy survey ever undertaken, snapping galaxy clusters, supernovae, the large-scale clumping of galaxies and weak gravitational lensing in the hunt for dark energy.
The survey is expected to begin in December, after the camera is fully tested, and will take advantage of the excellent atmospheric conditions in the Chilean Andes to deliver pictures with the sharpest resolution seen in such a wide-field astronomy survey.
In just its first few nights of testing, the camera has already delivered images with excellent and nearly uniform spatial resolution.
Over five years, the survey will create detailed colour images of one-eighth of the sky, or 5,000 square degrees, to discover and measure 300 million galaxies, 100,000 galaxy clusters and 4,000 supernovae.
"The Dark Energy Survey will help us understand why the expansion of the universe is accelerating, rather than slowing due to gravity," said Brenna Flaugher, project manager and scientist at Fermilab. "It is extremely satisfying to see the efforts of all the people involved in this project finally come together." | 0.859114 | 3.908951 |
Sept. 6 (UPI) -- A new analysis of Jupiter's auroras, the most powerful in the solar system, has revealed a fresh mystery.
"At Jupiter, the brightest auroras are caused by some kind of turbulent acceleration process that we do not understand very well," Barry Mauk, a researcher in the Applied Physics Laboratory at Johns Hopkins University, said in a news release.
Measurements of Jupiter's auroras using particle detectors and ultraviolet spectrographs revealed extremely large electric potentials. When electric potentials on Jupiter's poles align with the gas giant's magnetic field, electrons stream through the upper atmosphere at at energies upwards of 400,000 electron volts.
On Earth, large electric potentials are linked with the most intense auroras. Currents of a few thousand volts are associated with what are known as "discrete auroras," the famous colorful swirls snaking through the skies of Alaska and Scandinavia.
But when researchers looked for correlations between high electric potentials and intense auroras on Jupiter, they found no such link.
"There are hints in our latest data indicating that as the power density of the auroral generation becomes stronger and stronger, the process becomes unstable and a new acceleration process takes over," Mauk said. "But we'll have to keep looking at the data."
In other words, Jupiter's huge electric potentials at the poles don't explain the gas giant's massive auroras.
Jupiter exotic and dynamic atmosphere is oft studied by planetary scientists because it is capable of producing such dramatic forces. Previous research suggests Jupiter's intense auroras drive a series of massive storms, including the Great Red Spot.
The interplay between Jupiter's electromagnetic fields and climatic patterns could help scientists better understand other space-weather phenomena.
"The highest energies that we are observing within Jupiter's auroral regions are formidable," Mauk said. "These energetic particles that create the auroras are part of the story in understanding Jupiter's radiation belts, which pose such a challenge to Juno and to upcoming spacecraft missions to Jupiter under development."
Researchers detailed their analysis of Jovian auroras in a new paper published this week in the journal Nature. | 0.869417 | 3.739848 |
The final orbit of Venus by the Magellan spacecraft in October 1994 brought to a close an exciting period of Venus reconnaissance and exploration. The scientific studies resulting from data collected by the Magellan, Galileo, and Pioneer missions are unprecedented in their detail for any planet except Earth. Venus II re-evaluates initial assessments of Venus in light of these and other spacecraft missions and ground-based observations conducted over the past 30 years. More than a hundred contributors summarize our current knowledge of the planet, consider points of disagreement in interpretation, and identify priorities for future research. Topics addressed include geology, surface processes, volcanism, tectonism, impact cratering, geodynamics, upper and lower atmospheres, and solar wind environment. The diversity of the coverage reflects the interdisciplinary nature of Venus science and the breadth of knowledge that has contributed to it. A CD-ROM developed by the Jet Propulsion Laboratory accompanies the book and incorporates text, graphics, video, software, and various digital products from selected contributors to the text. A multimedia interface allows users to navigate the text and the extensive databases included on the disk. Venus II is the most authoritative single volume available on the second planet. Its contents will not only help shape the goals of future Venus missions but will also enhance our understanding of current Mars explorations. | 0.825481 | 3.026274 |
I’ve been a fan of Richard Feynman in that he is one of the few mainstream scientists that actually insisted that theories be consistent with the data, but also because he seemed so capable of thinking a problem through. Recently, I’ve been giving thought to his method of diagramming nuclear reactions, and one aspect of those diagrams is that they’re all reversible, and so are the reactions they represent.
This got me thinking about the role that neutrinos often play in nuclear reactions. If you fuse four hydrogen nuclei together (protons) to create a helium atom, two of these have to become neutrons in the process. Anytime protons convert to neutrons or the opposite, neutrinos are involved. In these reactions they are given off. But Feynman also suggests that these reactions can be played backwards, and in that case you’d have to have neutrinos coming into the reaction not leaving. That lead me to think that neutrinos must be capable of causing a nuclear reactions that wouldn’t otherwise happen. At first I wanted to say neutrino catalyzed reactions, but that really wouldn’t be correct because in this case they are consumed.
Never the less, we’ve been going through a period of anomalous activity in the solar system, not only is the Earth heating up, but so is Mars and every other planet that we can measure the temperature. The Earth is not only heating up on the surface, but there is evidence that things deep below are in flux as well. The rate that the magnetic field is wandering has increased dramatically over the last hundred years. There was a year a couple of decades ago where we had a serious of deep Earthquakes around the globe that exceeded the statistical norm for Earthquakes at depth by about a factor of ten. This, by the way, seems to have recently been expunged from the record and I have to wonder why. Anyway, the point is things are happening on this planet as well as others and our Sun, all at the same time, with no obvious connection.
I find myself wondering if neutrinos, even though the react with ordinary matter very little, might be responsible for increasing heat in planetary bodies by allowing nuclear reactions to happen that require them as one of the reactants, and if such nuclear systems might have a greater cross-section to neutrinos than ordinary matter making them a possible avenue to a more efficient and possibly selective neutrino detector. | 0.830061 | 3.467488 |
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Observing Equipment and Aids
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There's more to observing than just telescopes. Here are a few of the extra pieces of equipment at SBO that help astronomy students study and understand the sky.
There's probably no observing aid so useful for learning the
night sky as a planisphere, or star-wheel. The observer
dials in the current date and time - or equivalently, the
local sidereal time - and the resulting window shows an
accurate sky map of everything that's "up".
But most starwheels have a couple of problems. They're small, so an instructor has difficulty showing several students at a time around the sky. And, of course it's dark outside where you need to look at it. Juggling a flashlight makes things more complicated, and also defeats your night vision when comparing the map with the sky overhead.
The Observatory has largely overcome these difficulties with its 40-inch diameter planisphere mounted on the south wall of the Observing Deck. Its sheer size makes it convenient for group use. The skymap is dimly back-lit, so that one can identify the star patterns without turning on additional lights. And, it's also motor driven to automatically keep track of the sky over the course of the night.
Here's how this unusual stargazing tool was designed and built.
Every astronomical facility should have some, and SBO is no
exception. Binoculars are excellent tools for viewing large
bright sky objects such as the Moon, the Pleiades and other
large open clusters, Andromeda and Pinwheel galaxies, and
some diffuse nebula such as M42 and M8.
Our binoculars range from a set of handheld inexpensive 7x50s (7 power, 50 mm lens diameter) - "pass 'em out, and hope that we get 'em back" - to tripod-mounted 11x70s and 20x80s . The Gemini mirror mount is for those who prefer the convenience of sitting at a table and looking down.
Although CCD imaging has largely replaced photography,
there's still a use for 35mm photography. SBO keeps several
camera backs (Nikon F's, and Pentax K1000's) available for
students who don't own a manual SLR camera but still want to
shoot for the stars.
For observers that bring their own camera backs, we also have a large collection of T-adapters to mate virtually any SLR camera back to an eyepiece holder mount.
The SSP-3 eyepiece photometer from Optec provides an easy
and accurate way to do photometry on individual bright
stars. The photometer simply replaces the eyepiece at a
telescope. A flip-mirror switches between the detector and
an eyepiece for focussing and pointing.
Slide-in filters permit intensity measurements in five different spectral bands from the near ultraviolet to the near infrared: U, B, V, R, and I. Added versatility is obtained with three sensitivity scales and two different integration times. Signal output can be fed to an A/D converter and computer, for real-time logging of transient events such as occultations. | 0.82956 | 3.523685 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2000 March 9
Explanation: Late last month another erupting filament lifted off the active solar surface and blasted this enormous bubble of magnetic plasma into space. Direct light from the sun is blocked in this picture of the event with the sun's relative position and size indicated by a white half circle at bottom center. The field of view extends 2 million kilometers or more from the solar surface. While hints of these explosive events, called coronal mass ejections or CMEs, were discovered by spacecraft in the early 70s this dramatic image is part of a detailed record of this CME's development from the presently operating SOlar and Heliospheric Observatory (SOHO) spacecraft. Near the minimum of the solar activity cycle CMEs occur about once a week, but as we approach solar maximum rates of two or more per day are anticipated. Though this CME was clearly not headed for Earth, strong CMEs are seen to profoundly influence space weather, and those directed toward our planet and can have serious effects.
Authors & editors:
Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
& Michigan Tech. U. | 0.831608 | 3.03794 |
Scientists at the University of Geneva who are looking for planets outside our solar system have found one with a unique feature: a huge tail made of gas.
The exoplanet GJ 436b, as the tailed planet is called, orbits its central star very closely and therefore loses part of its atmosphere because of the star’s intense heat. The dissipating atmosphere takes on the look of a comet’s tail, perpetually following the planet.
Although the international research team working in Geneva discovered the planet years ago, they have only now been able to observe the full tail using the Hubble space telescope. Previously, as GJ 436b passed in front of a star, the team had surmised that a gas tail was obscuring it from view but they were unable to get a closer look to confirm until this week.
The rare observation will allow scientists to better understand how stars affect the atmospheres of the planets that orbit them, the researchers said in their paper detailing the finding in the journal “Astronomy and Astrophysics”.
In addition to the University of Geneva, the research team comprises scientists from the University of Bern as well as France and Britain.
swissinfo.ch and agencies/vdv | 0.913868 | 3.164063 |
Using data from the IceCube Neutrino Observatory at the South Pole, scientists have reported progress in understanding the longstanding mystery of how and where cosmic rays originate, in a development that might help us find ways to shield astronauts and electronics from cosmic radiation.
What is a cosmic ray?
The term cosmic ray is a misnomer. In truth, these are not rays but rather charged particles made up primarily of high-energy protons and atomic nuclei that travel throughout interstellar space at extremely high speeds.
We still don't know how cosmic rays accelerate as they travel through space, and we also know very little about where they originate. Since they are charged particles, their trajectory is bent multiple times by the interstellar magnetic fields they find along their way, which makes it much harder to deduce where they originally came from.
Cosmic rays are thought to be the highest-energy particles in the universe. Some can reach energies of 300 EeV, which is forty million times the energy at which particles collide at the Large Hadron Collider and approximately the kinetic energy of a tennis ball being served at 115 km/h (70 mph).
Why do we care about cosmic rays?
You may argue that the money for building powerful new telescopes is ill-spent because the knowledge they produce is essentially useless to us, but in the case of cosmic rays, you'd be very wrong. Cosmic rays are already a concern for the space and the electronics industry today, and their impact is destined to become even more serious over the next few decades – which is why any development in this area is generally welcomed with open arms.
The Earth's magnetic field shields us from the vast majority of cosmic particles, but outside the comfort of our little bubble the threat of cosmic radiation can be very real. These particles can be dangerous because their incredibly high energy is enough to knock off DNA molecules and disrupt electronics.
Thanks to recent experiments, we can now estimate that unshielded humans in space should expect a dose of 400 to 900 milliSieverts a year (compared to 2.4 on Earth). Radiation doses over 4 Sieverts are considered extremely dangerous and potentially lethal, meaning that while short trips in space don't pose a real radiation threat, a long-term mission to Mars would necessitate effective ways to shield the crew from radiation.
As for electronics, high-energy cosmic rays have enough force to alter the bits inside integrated circuits and cause transient errors to occur. Back in the 1990s, an IBM study estimated that cosmic rays induce one error per 256 megabytes of RAM per month, and the problem will only get tougher as electronics become smaller and smaller. (In 2008, Intel went as far as patenting a cosmic ray detector to integrate inside their next-gen CPUs.)
What did we find out?
The flux of cosmic rays that hit the surface of the Earth can be analyzed and classified both by energy and chemical composition in order to learn more about their origin, the way in which they are accelerated, their energy spectrum and their composition: information that might help us build an effective shielding mechanism.
When ultra high energy cosmic rays are produced, they are accompanied by ultra high energy neutrinos. Neutrinos are chargeless and almost massless particles that rarely interact with other matter. As a result, unlike cosmic rays, they travel in a straight line and can be traced back to their source.
"On rare occasions when neutrinos interact with matter, they produce charged particles," University of Delaware physicist Bakhtiyar Ruzybayev, corresponding author of a paper on this study, tells Gizmag. "And when this charged particles go through transparent medium at speeds faster than light (in that medium), they emit light. Most neutrino detectors are built to detect that light."
Using neutrino detectors such as the one at IceTop, scientists have observed a relationship between the energy of cosmic rays and their flux (that is, how often they hit a given area). Particles thought to originate from the Milky Way generally have lower energy but are much more frequent, while particles from much further away are harder to come by and are also higher-energy because they had been accelerating for a much longer time before they finally hit Earth.
A constant acceleration would dictate a simple power law between flux and the energy of the particle (which would look like a single straight line in the logarithmic graph above); however, things aren't that simple, and scientists have detected a steepening of the curve, which they call the "knee." To the left of the knee are lower-energy particles that are mostly coming from our own galaxy, while to its right are mostly extra-galactic cosmic rays. A second feature, the "ankle," describes the graph where higher-energy particles are involved.
The recent findings by the University of Delaware scientists are that things are even more complicated than they look. The cosmic-ray energy spectrum does not follow a simple power law between the knee around 4 PeV (peta-electron volts) and the ankle around 4 EeV (exa-electron volts), as previously thought, but exhibits features like hardening around 20 PeV and steepening around 130 PeV.
The graph above illustrates the findings, with the data zooming in around the knee of the previous graph. Their significance is that the acceleration and propagation of cosmic rays adheres to laws that are less predictable than previously thought. "These measurements provide new constraints that must be satisfied by any models that try to explain the acceleration and propagation of cosmic rays," Ruzybayev explained.
The findings appear in the journal Physical Review D.
Source: University of Delaware | 0.804508 | 4.110293 |
Over the years we’ve had some pretty amazing comets swing by our planet. I remember the ones I’ve seen myself: Hyakutake, Hale-Bopp, Holmes, Pan-STARRS, McNaught… they were all beautiful and amazing sights.
Now we have C/2012 S1 (ISON) passing our way, and it’s certainly grabbing attention. It’s brightened substantially in just the past few days, so now’s the time to see it! The pictures people are taking are phenomenal, and there’s plenty of science pouring in as well.
Everyone loves a good picture, of course, but comets are amazing well beyond just their stunning beauty. So I figured I’d take this opportunity to tell you a few things about this comet, a handful of facts to nourish the part of your brain seeking out wonder. Keep these in mind while you’re gawking at the gorgeous pictures.
1) ISON is a n00b.
Some comets are on long, elliptical orbits dropping them in to the inner solar system before sailing them back out to the depths of space. There, they slow, stop, then fall once again back into the warmth and light. Comet Halley, for example, is on a 75-year orbit that takes it out past Neptune.
But some are more extreme. If they get an extra kick on their way in — perhaps from a collision, or a boost by a planet’s gravity — their elliptical orbit gets turned into an open-ended hyperbola: they have more than enough energy to leave the solar system forever. Once they’re gone, they’re gone.
ISON is a hyperbolic comet, which means this is it: These next few weeks are our only chance to see it. After it swings back out, it ain’t coming back. This is likely its first tour of the inner solar system as well, which is why scientists are so excited about it; we’re seeing a pristine comet, billions of years old, a relic of the ancient solar system. It’s a time capsule, letting us study what conditions were like when the Sun and planets were young.
2) ISON is a sun-diver.
The orbit of ISON takes it very, very close to the Sun’s surface. Next week, on Nov. 28, it will skim a mere 1.1 million kilometers (about 700,000 miles) above the Sun’s surface. Given that the Sun is 1.4 million km across, that’s a mighty close shave! The heat it feels will be intense, and it may not survive the encounter (see #10 below).
3) When it passes the Sun, it will be moving at 360 kilometers per second.
Imagine dropping a rock. The higher you drop it, the longer the Earth’s gravity has to pull on it, and the faster it’ll be moving when it hits the ground.
The fastest a rock can hit the Earth is if you drop it from infinitely far away. When it hits it’ll be moving at escape velocity — and the physics of dropping it is reversible, so if you throw a rock at escape velocity it will continue on forever (hence the term "escape velocity").
The same is true for a comet rounding (or, in some cases, impacting) the Sun. Since ISON is falling from essentially infinitely far away, when it goes around the Sun it’ll be moving at the Sun’s escape velocity at that distance, or just about 360 km/sec (225 miles/sec). How fast is that? Well, it's hundreds of times faster than rifle bullet, for example, and over 1500 times faster than a commercial jet — at that speed, the comet would cross the continental United States in about 15 seconds.
In fact, it will be moving at 0.1% the speed of light! That’s far faster than any human-made space probe has ever traveled. And the only propulsion it uses is gravity.
[CORRECTION (Nov. 22, 2013 at 16:15 UTC): I made an error in the calculation for this section, using the escape velocity for the Sun's surface, and not for the distance ISON will be from the Sun's center. This deserves a longer explanation, so I wrote a follow-up post about it, and simply corrected the problem here.]
4) The solid part of ISON is only about two kilometers across.
Comets are actually lumps of rock, gravel, and ice mixed together. This solid part of the comet is called the nucleus, and some are huge; Hale-Bopp had a nucleus about 30 km (20 miles) across.
ISON, though, is tiny, only about 2 km (1.2 miles) across. Heck, plop it down in the middle of the Rocky Mountains and you’d hardly notice it! The size has been estimated using images taken from the Hubble Space Telescope, which in reality only give us an upper limit. It might even be smaller.
Still, that’s enough to make the comet visible to the naked eye even from a distance of a hundred million kilometers! How can that be? Why, it’s because…
5) The coma is well over 100,000 km in size.
When you look at a picture of ISON (or any comet), you’re not seeing the nucleus. You’re seeing the gas surrounding it that was once frozen beneath the surface. When the comet gets near the Sun this ice warms and turns directly into a gas. It escapes the weak gravity of the nucleus, forming the fuzzy coma around it.
Since the coma isn’t solid, it doesn’t have a sharp edge. But on Nov. 15, the coma for ISON was estimated to appear about 3 arcminutes across (that’s a size on the sky; the Moon is 30 arcminutes across for comparison). Since ISON was about 140 million km (90 million miles) from Earth at the time, that would put the coma at a size of about 120,000 km (80,000 miles). That’s ten times the diameter of Earth!
6) The tail of the comet is (at least) 8 million kilometers long.
Once the gas (and ejected dust) in the coma is out in space, it can be affected by both the solar wind and the pressure of sunlight. It streams away, forming one or more long tails. Like the coma, this is extremely rarefied gas, so it doesn’t really have an edge, but the tail of ISON has been measured to be at least 8 million km (5 million miles) long. That’s 20 times the distance of the Moon from the Earth.
7) The tail is essentially a vacuum.
Weirdly, despite being bright and obvious, a comet’s tail is incredibly ethereal. The density of atoms in a typical tail can run up to about 50,000 atoms per cubic centimeter. Sound like a lot? In a cubic centimeter of air at sea level, there are 1019 (10,000,000,000,000,000,000) atoms/molecules per cc! Compared to the air we breathe, a comet’s tail is a hard vacuum. It’s only bright because it’s so big, and reflects sunlight.
8) The total mass of the comet is about 2 - 3 billion tons.
Ice isn’t terribly dense; it floats on water! If ISON is a typical mix of ice and rock, it has a density of about 600 kg per cubic meters. Assuming it’s a sphere two km across, that gives it a mass of roughly 2 - 3 billion tons. That may sounds like a lot, but remember, ice is far less dense than rock. A small rocky mountain would be far more massive.
9) ISON is shrinking.
Measurements of how much water ice is leaving the comet’s surface indicate it’s losing about 1029 molecules of water every second (bearing in mind this goes up and down all the time). Doing the math, I get that this is about three tons per second — enough to fill an Olympic pool in about ten minutes. That’s a fair amount, but given the total mass of the comet, it would take about 25 years at this rate for the comet to totally disappear. Since it’s only shedding mass for the few weeks it’s near the Sun, it’s got mass to spare. Thanks to @SungrazingComets and the Comet ISON Observing Campaign for their help with this.
10) ISON may disintegrate
That doesn’t mean it’s safe, though! Some comets aren’t terribly solid; the ice is what holds them together. As they near the Sun and the ice starts to go away, big chunks can break off (called “calving”). In some cases the comet can disintegrate spectacularly. Even if they survive their plunge down to the Sun, some comets get so close they evaporate; we’ve seen that happen too!
It’s not clear if ISON will survive its close shave with the Sun. As of right now it seems to be OK, but who knows what the next few days will bring.
11) ISON won’t hit the Earth.
Whenever there’s a bright comet (or near pass of an asteroid), conspiracy buffs start thinking it’ll hit us. Don’t worry about ISON. The closest it will get is on Dec. 26, 2013, when it will be about 60 million km (40 million miles) from Earth. That’s 150 times farther away than the Moon.
12) You can see it for yourself, and it may become visible in broad daylight.
Right now, ISON is bright enough to see naked eye, and easily with binoculars. It’s jumped in brightness twice just in the past week or so! As it gets near the Sun it’ll get brighter, but harder to find because, duh, it’s getting near the Sun.
However, sometimes comets like this get incredibly bright when they are close to the Sun. In 2007, I saw comet McNaught at noon. Yes, noon. It was difficult, and I had to be very careful; you don’t want to wind up looking right at the Sun, especially in binoculars, unless boiled eyeballs is something you want. Seriously, don’t just scan around with binoculars looking for the comet, because it’s very dangerous and can blind you.
There’s no way to know right now, but it’s possible that ISON will be visible in broad daylight to the naked eye for the short time it’s near the Sun. It could be possible to see it during the day if you position yourself so that the Sun is blocked behind a tree, or the edge of a house. It depends on the exact position of the comet relative to the Sun, of course.
Again, doing this is difficult and you shouldn't attempt it unless you know what you’re doing. I’ll note that in general, glancing briefly at the Sun won’t hurt a normal eye with an undilated pupil, but it’s not a good idea to do it too much, and it’s more dangerous for kids (their lenses let through more UV light than adult eyes).
Your better bet is to wait a few more days. Once ISON rounds the Sun, it’ll be visible in the west after sunset for a few weeks for those of us in the northern hemisphere, so watching it will be far easier (right now you have to get up at about 5:00 a.m., before sunrise, to see it). Here’s a finder chart (Sky and Telescope has another as well) that’ll help you spot it; planetarium software for mobile devices are great too (I like Sky Safari, but there are many to choose from). You can find plenty more finder charts online. I’ll note it’ll fade with time, but around Dec. 20 or so it should be out of the Sun’s glare, and (hopefully) easily visible with binoculars. [UPDATE (Nov. 22, 2013 at 16:15 UTC): I'll note that once it passes the Sun, the comet will still be visible in the east before sunrise in the morning as well as in the west after sunset in the evening. I explain this in a follow-up post.]
Seeing a good comet is a wonderful experience, and ISON gives us a chance to experience something that will only come around once, quite literally. This isn’t science fiction, or something out of a movie: This object exists, and it’s just one small part of a much grander universe that’s out there. I hope you can take a moment to drink that in. | 0.843192 | 3.634348 |
ann1008 — Announcement
Hubble Gives Clues about Saturn’s “Irregular Heartbeat”
4 August 2010
A European-led team has used the NASA/ESA Hubble Space Telescope to make a startling discovery about Saturn, the Solar System’s second largest planet . The astronomers discovered that Saturn’s aurora, an ethereal ultraviolet glow that illuminates its upper atmosphere near the poles, dances in time to the beat of a mysterious radio emission.
For years, scientists thought that the Saturn Kilometric Radiation (SKR), which shines from Saturn’s polar regions, pulsed in time with the rotation of the planet. However, more recent studies have shown that the rate speeds up and slows down with time. Since planets spin at a constant rate, Saturn’s rotation cannot explain an irregular pulsing of the SKR.
The team, led by the University of Leicester’s Jonathan Nichols, has discovered that the planet’s aurora varies in time with the SKR, pointing to a common explanation for both.
Nichols says: “This is an important discovery for two reasons. First, it provides a long-suspected but hitherto missing link between the radio and auroral emissions, and second, it adds a critical tool in diagnosing the cause of Saturn’s irregular heartbeat.”
The paper, “Variation of Saturn’s UV aurora with SKR phase”, will be published on Friday 6 August in the journal Geophysical Research Letters.
A full press release and further details of the discovery are available from the University of Leicester.
- Research paper
- More info: University of Leicester press office
- The team’s observations of Saturn were previously featured in a Hubble photo release, available at: http://www.spacetelescope.org/news/heic1003/
Dr Jonathan Nichols
Radio and Space Plasma Physics Group
Physics and Astronomy Department
University of Leicester
Tel: +44 (0)116 252 5049
Junior Hubble/ESA Public Information Officer
About the Announcement | 0.811018 | 3.223286 |
Supernova Remnant Turns 400
Four hundred years ago, sky watchers, including the famous astronomer Johannes Kepler, were startled by the sudden appearance of a "new star" in the western sky, rivaling the brilliance of the nearby planets. Now, astronomers using NASA's three Great Observatories are unraveling the mysteries of the expanding remains of Kepler's supernova, the last such object seen to explode in our Milky Way galaxy.
This combined image -- from NASA's Spitzer Space Telescope, Hubble Space Telescope, and e Chandra X-ray Observatory -- unveils a bubble-shaped shroud of gas and dust that is 14 light-years wide and is expanding at 4 million miles per hour (2,000 kilometers per second). Observations from each telescope highlight distinct features of the supernova remnant, a fast-moving shell of iron-rich material from the exploded star, surrounded by an expanding shock wave that is sweeping up interstellar gas and dust.
Photo Credit: NASA
+ View Full Image
+ View Images Used to Make Composite
+ Zoom to the supernova remnant -- 1.2 Mb MPEG
+ View composite image split into its three components -- 940 Kb MPEG
+ View animation of a supernova explosion -- 894 Kb MPEG | 0.889214 | 3.23777 |
June 3, 2005
Mineral on Mars Suggests Dry Local History
HONOLULU, Hawaii -- By using new, high spatial resolution infrared data from NASA's Mars Odyssey spacecraft, Victoria Hamilton from the University of Hawaii at Manoa and Philip Christensen from Arizona State University have concluded that a region on the surface of Mars known to contain olivine-rich rocks is actually 4 times larger than previously estimated.
The bedrock in question is adjacent to Syrtis Major, one of Mars' largest volcanoes. This region is of interest to scientists because it lies in a relatively old region on Mars, and yet contains significant amounts of olivine, a mineral that can weather rapidly in the presence of water.These results are reported in the June 2005 cover story of the journal Geology.
Based on its infrared spectral signatures, this region was previously identified by the NASA Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) (launched in 1996) as having an enrichment in the mineral olivine (the dominant mineral component of several Martian meteorites) relative to typical Martian basalts. Infrared spectra of rocks are like fingerprints, allowing scientists to determine their mineral make-up.
Using higher spatial resolution data available from the Mars Odyssey spacecraft's Thermal Emission Imaging System (THEMIS) (launched in 2001), the researchers were able to expand the boundaries of the high-olivine region by comparing the infrared spectra and temperature measurements acquired by THEMIS to geological features in visible wavelength digital images taken by THEMIS and the MGS Mars Orbiter Camera.
"By having the different types of high resolution visible, spectral, and temperature information available, we were able to see both geochemical and geological features on Mars that showed us that this high-olivine region is much larger than we thought previously," said Hamilton, an assistant professor in the Hawaii Institute of Geophysics and Planetology. "We now have a better view of the detailed geology of this ancient region."
The region is northeast of the Syrtis Major volcanic shield, and was previously shown to have an area of ~ 30,000 km 2. In this new study, the deposits in question are now shown to be 113,000 km 2, almost 4 times larger than previously thought. As a comparison, the Big Island of Hawai'i, with its five volcanoes, has a surface area of ~10,500 km 2 "“ almost 11x smaller than the deposits on Mars.
These olivine-rich basalts appear to be present in the form of in-place, layered rock units that are being exposed by tectonic uplift and the erosion of younger rocks. One of the findings of the study is that at least some of these rocks were erupted onto the surface of Mars, where they might have been exposed to more water and weathering than if they had been intruded into the subsurface, as previously proposed.
"How much liquid water was present on the surface of Mars in the past, and for how long, are big questions in planetary science right now," Hamilton says. "Under many conditions, olivine turns into other minerals very rapidly in the presence of water, so the preservation of all this olivine in a very old region of Mars is intriguing. One hypothesis is that this area of Mars has not seen much water. Now that we know the detailed distribution of these olivine-rich rocks, we can search more of the spectral data for minerals that might have formed if the olivine was exposed to water at some point in its past. "
This research is covered in the June issue of the GEOLOGY, published by the Geological Society of America, and is featured on the magazine's cover.
This research was funded through grants from the National Aeronautics and Space Administration (NASA).
Research article citation:
Evidence for extensive, olivine-rich bedrock on Mars, Victoria E. Hamilton and Philip R. Christensen, Geology, Volume 33, Number 6, June 2005. http://www.gsajournals.org
About the School of Ocean and Earth Science and Technology
The School of Ocean and Earth Science and Technology (SOEST) was established by the Board of Regents of the University of Hawaii in 1988. SOEST brings together in a single focused ocean, earth sciences and technology group, some of the nation's highest quality academic departments, research institutes, federal cooperative programs, and support facilities to meet challenges in the ocean and earth sciences, including the Hawaii Institute of Geophysics and Planetology (HIGP). Scientists at SOEST are supported by both state and federal funds as they endeavor to understand the subtle and complex interrelations of the seas, the atmosphere, and the earth.
On the Net: | 0.835802 | 3.855211 |
WASHINGTON — NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft has returned data that indicate ice may make up as much as 22 percent of the surface material in a crater located on the moon’s south pole.
The team of NASA and university scientists using laser light from LRO’s laser altimeter examined the floor of Shackleton crater. They found the crater’s floor is brighter than those of other nearby craters, which is consistent with the presence of small amounts of ice. This information will help researchers understand crater formation and study other uncharted areas of the moon. The findings are published in Thursday’s edition of the journal Nature.
“The brightness measurements have been puzzling us since two summers ago,” said Gregory Neumann of NASA’s Goddard Space Flight Center in Greenbelt, Md., a co-author on the paper. “While the distribution of brightness was not exactly what we had expected, practically every measurement related to ice and other volatile compounds on the moon is surprising, given the cosmically cold temperatures inside its polar craters.”
The spacecraft mapped Shackleton crater with unprecedented detail, using a laser to illuminate the crater’s interior and measure its albedo or natural reflectance. The laser light measures to a depth comparable to its wavelength, or about a micron. That represents a millionth of a meter, or less than one ten-thousandth of an inch. The team also used the instrument to map the relief of the crater’s terrain based on the time it took for laser light to bounce back from the moon’s surface. The longer it took, the lower the terrain’s elevation.
In addition to the possible evidence of ice, the group’s map of Shackleton revealed a remarkably preserved crater that has remained relatively unscathed since its formation more than three billion years ago. The crater’s floor is itself pocked with several small craters, which may have formed as part of the collision that created Shackleton.
The crater, named after the Antarctic explorer Ernest Shackleton, is two miles deep and more than 12 miles wide. Like several craters at the moon’s south pole, the small tilt of the lunar spin axis means Shackleton crater’s interior is permanently dark and therefore extremely cold.
“The crater’s interior is extremely rugged,” said Maria Zuber, the team’s lead investigator from the Massachusetts Institute of Technology in Cambridge in Mass. “It would not be easy to crawl around in there.”
While the crater’s floor was relatively bright, Zuber and her colleagues observed that its walls were even brighter. The finding was at first puzzling. Scientists had thought that if ice were anywhere in a crater, it would be on the floor, where no direct sunlight penetrates. The upper walls of Shackleton crater are occasionally illuminated, which could evaporate any ice that accumulates. A theory offered by the team to explain the puzzle is that “moonquakes”– seismic shaking brought on by meteorite impacts or gravitational tides from Earth — may have caused Shackleton’s walls to slough off older, darker soil, revealing newer, brighter soil underneath. Zuber’s team’s ultra-high-resolution map provides strong evidence for ice on both the crater’s floor and walls.
“There may be multiple explanations for the observed brightness throughout the crater,” said Zuber. “For example, newer material may be exposed along its walls, while ice may be mixed in with its floor.”
The initial primary objective of LRO was to conduct investigations that prepare for future lunar exploration. Launched in June 2009, LRO completed its primary exploration mission and is now in its primary science mission. LRO was built and is managed by Goddard. This research was supported by NASA’s Human Exploration and Operations Mission Directorate and Science Mission Directorate at the agency’s headquarters in Washington.
NASA RELEASE : 12-208 | 0.82405 | 3.890331 |
Rocket Science Meets X-Ray Science
Credit: Marilyn Chung/Berkeley Lab
It takes rocket science to launch and fly spacecraft to faraway planets and moons, but a deep understanding of how materials perform under extreme conditions is also needed to enter and land on planets with atmospheres. X-ray science is playing a key role, too, in ensuring future spacecraft survive in extreme environments as they descend through otherworldly atmospheres and touch down safely on the surface.
Scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and NASA are using X-rays to explore, via 3-D visualizations, how the microscopic structures of spacecraft heat shield and parachute materials survive extreme temperatures and pressures, including simulated atmospheric entry conditions on Mars.
Human exploration of Mars and other large-payload missions may require a new type of heat shield that is flexible and can remain folded up until needed. Candidate materials for this type of flexible heat shield, in addition to fabrics for Mars-mission parachutes deployed at supersonic speeds, are being tested with X-rays at Berkeley Lab’s Advanced Light Source (ALS) and with other techniques.
“We are developing a system at the ALS that can simulate all material loads and stresses over the course of the atmospheric entry process,” said Harold Barnard, a scientist at Berkeley Lab’s ALS who is spearheading the Lab’s X-ray work with NASA.
The success of the initial X-ray studies has also excited interest from the planetary defense scientific community looking to explore the use of X-ray experiments to guide our understanding of meteorite breakup. Data from these experiments will be used in risk analysis and aid in assessing threats posed by large asteroids.
The ultimate objective of the collaboration is to establish a suite of tools that includes X-ray imaging and small laboratory experiments, computer-based analysis and simulation tools, as well as large-scale high-heat and wind-tunnel tests. These allow for the rapid development of new materials with established performance and reliability.
This system can heat sample materials to thousands of degrees, subject them to a mixture of different gases found in other planets’ atmospheres, and with pistons stretch the material to its breaking point, all while imaging in real time their 3-D behavior at the microstructure level. NASA Ames Research Center (NASA ARC) in California’s Silicon Valley has traditionally used extreme heat tests at its Arc Jet Complex to simulate atmospheric entry conditions.
Researchers at ARC can blast materials with a giant superhot blowtorch that accelerates hot air to velocities topping 11,000 miles per hour, with temperatures exceeding that at the surface of the sun. Scientists there also test parachutes and spacecraft at its wind-tunnel facilities, which can produce supersonic wind speeds faster than 1,900 miles per hour.
Michael Barnhardt, a senior research scientist at NASA ARC and principal investigator of the Entry Systems Modeling Project, said the X-ray work opens a new window into the structure and strength properties of materials at the microscopic scale, and expands the tools and processes NASA uses to “test drive” spacecraft materials before launch.
“Before this collaboration, we didn’t understand what was happening at the microscale. We didn’t have a way to test it,” Barnhardt said. “X-rays gave us a way to peak inside the material and get a view we didn’t have before. With this understanding, we will be able to design new materials with properties tailored to a certain mission.”
He added, “What we’re trying to do is to build the basis for more predictive models. Rather than build and test and see if it works,” the X-ray work could reduce risk and provide more assurance about a new material’s performance even at the drawing-board stage.
Francesco Panerai, a materials scientist with NASA contractor AMA Inc. and the X-ray experiments test lead for NASA ARC, said that the X-ray experiments at Berkeley Lab were on samples about the size of a postage stamp. The experimental data is used to improve realistic computer simulations of heat shield and parachute systems.
“We need to use modern measurement techniques to improve our understanding of material response,” Panerai said. The 3-D X-ray imaging technique and simulated planetary conditions that NASA is enlisting at the ALS provide the best pictures yet of the behavior of the internal 3-D microstructure of spacecraft materials.
The experiments are being conducted at an ALS experimental station that captures a sequence of images as a sample is rotated in front of an X-ray beam. These images, which provide views inside the samples and can resolve details less than 1 micron, or 1 millionth of a meter, can be compiled to form detailed 3-D images and animations of samples.
This study technique is known as X-ray microtomography. “We have started developing computational tools based on these 3-D images, and we want to try to apply this methodology to other research areas, too,” he said.
This article has been republished from materials provided by Berkeley Lab. Note: material may have been edited for length and content. For further information, please contact the cited source.
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Photographing the invisible using infrared light
In 1800, the German astronomer William Herschel was the first to discover that light is not always visible to the naked eye. During an optical experiment, Herschel passed sunlight through a prism to separate the white light into its coloured components. Using a thermometer, he measured the temperature of each of the coloured rays and determined that the temperature increased from blue to red.
Pushing his experiment a little bit further, Herschel placed the thermometer beyond the red light rays where no light was visible. To his great surprise, he measured a temperature even higher than that within any of the visible rays. He proved, for the first time ever, that invisible light – the infrared – exists beyond the red portion of the light spectrum.
In 1856, the Scottish astronomer Charles Piazzi Smyth detected infrared light emanating from the Moon. He conducted his observations at different elevations and realized that the best data had been collected at the highest elevations. He was thus the first to understand that the terrestrial atmosphere absorbs some part of the infrared light coming from space.
In 1880, the British chemist William de Wiveleslie Abney was the first to take an infrared photograph. It was an image of a hot teapot that he recorded using a special collodion emulsion. Unfortunately, the composition of the collodion was not revealed and, for the next twenty years, all attempts to produce another infrared photograph failed.
The first publicly known infrared-sensitive chemical compound, dicyanine, was discovered in 1903. One year later, the American physicist Robert Williams Wood recognized the possibility of improving the sensitivity of infrared photographic film using kryptocyanine emulsion, the chemical cousin of dicyanine. He conducted experiments and, in 1910, became the first to publish photographs taken in the infrared (the photos were of scenery).
Knowing that the terrestrial atmosphere absorbs some of the infrared rays coming from space, astronomers (both amateurs and professionals) began to collect airborne data beginning in the 1930’s.
It was during one of these expeditions that the American Albert William Stevens used an infrared filter in 1932 to photograph a total eclipse of the Sun from an airplane at an altitude of 8,200 metres. In 1933, an American, Auguste Piccard, used an infrared camera to photograph the Earth’s ozone layer from onboard the hot air balloon Century of Progress.
In 1942, the Eastman Kodak Company patented the first infrared-sensitive film that could produce photos using “false colours”. The Swedish company AGA/Bofors put the first infrared camera for industrial use on the market in 1968. One of its uses is to find defaults in electrical lines
Telescopes borne on rockets were first used to photograph the infrared sky in 1970. The project, called Hi Star, was active until 1976 and managed to accumulate a total of 30 minutes of observation time. In all, 2,363 infrared sources were detected.
The first infrared space observatory – IRAS (Infrared Astronomical Satellite) – was launched in 1983 and operated for 10 months. It mapped more than 96% of the sky and discovered about 500,000 infrared sources. The ability of infrared light to pass through dust allowed the centre of our galaxy, the Milky Way, to be revealed for the first time.
In 1989, the COBE (Cosmic Background Explorer) satellite was launched into orbit and the entire infrared sky was mapped in four years. A few years later, in 2003, the Spitzer space telescope was launched. Spitzer is the “Rolls-Royce” of infrared telescopes and is used to study specific astronomical targets. | 0.865707 | 3.790167 |
The most precise measurement yet of the Hubble parameter illuminates dark energy — the elusive entity that’s accelerating the universe’s expansion.
Astronomers have used data from the Sloan Digital Sky Survey (SDSS) to precisely map the structure of the young universe. The most recent analysis, released on April 7th, pins down the expansion rate of the universe when it was only one-quarter of its present age.
"It's the most precise measurement of the Hubble parameter at any redshift (cosmic epoch), even better than the measurement we have from the local universe," says lead author Andreu Font-Ribera (University of Zurich, Switzerland, and Lawrence Berkeley National Laboratory)
SDSS utilizes millions of galaxies and thousands of quasars to illuminate the universe across multiple cosmic epochs, expanding our understanding of how the universe has evolved over its 13.8 billion years and shedding light on dark energy.
An Accelerating Universe
Since the Big Bang the universe has been expanding: the fabric of spacetime is stretching and carrying galaxies away from one another. But gravity — known for its ability to keep the Moon in orbit around Earth and bind together enormous clusters of galaxies — would certainly slow down the expansion as time went on. Or so we thought.
It came as a surprise when the data showed the opposite: the expansion is speeding up.
The best explanation for the universe’s surprising acceleration is some mysterious antigravity, a dark energy embedded in space itself.
The universe’s expansion rate depends directly on the density of energy in space. It may be characterized with the Hubble parameter, H, or the ratio of a faraway galaxy’s velocity to its distance. While a relatively simple concept, its units are slightly wacky at km/s per megaparsec (a parsec is 3.26 lightyears).
Ever since the universe’s birth, both dark energy and gravity have been in a cosmic tug of war. For the first 8 billion years, gravity dominated, and cosmic expansion did slow down as expected. The universe was smaller and denser, making the Hubble parameter extremely large.
But as matter in the cosmos thinned out, gravity’s pull weakened and dark energy began to take over. The cosmic expansion stopped slowing and started accelerating. The Hubble parameter decreased rapidly. We’re in an era where the Hubble parameter is constant at approximately 73 km/s/Mpc.
Dark energy is a mind-boggling concept, but astronomers are pretty sure about it. Compelling evidence found in the cosmic microwave background and the clustering of galaxies also strongly support its existence.
Tracking Dark Energy Over Time
Now a project known as the Baryon Oscillation Spectroscopic Survey (BOSS), the largest component of the third Sloan Digital Sky Survey, is tracking dark energy over time. And it’s doing so with an amazing degree of precision.
A team led by Timothée Delubac (Centre de Saclay, France, and Federal Polytechnic Institute of Lausanne, Switzerland) has utilized and further constrained methods generated by Font-Ribera’s team to establish a Hubble parameter of 222 ± 6 km/s/Mpc at a redshift of 2.34, over 10 billion years ago.
This result shows that if the universe were less than a quarter of its present age, we would see that a pair of galaxies separated by 1 Mpc, or roughly 3 million light-years, would be moving away from each other at a rate of 222 km/s.
How can astronomers measure the Hubble parameter throughout cosmic time?
When the universe was young and extremely hot, overly dense spots of matter struggled between the inward pull of gravity and the outward push of radiation pressure from the photons in the plasma. This struggle sent waves rippling outward into space, somewhat like those created by a rock hitting water. The acoustic waves reverberated through the dense, hot plasma at speeds approaching the speed of light.
But once the universe cooled enough that atoms formed and photons could travel freely, the radiation pressure that was fueling the sound waves disappeared, causing them to leave slightly over-dense shells imprinted in the universe's matter. These ripple-like signatures — called baryon acoustic oscillations — continued to expand with the universe. Today their mark can be seen on the structure and spacing of the giant sheets and filaments of galaxies that later evolved.
The regular spacing between these structures creates a natural cosmic yardstick. By comparing the present-day size of these ripples (roughly 500 million light-years) with their size just after the universe cooled, we can learn how space has stretched over time.
But beyond a redshift of 0.7 (roughly 6 billion years ago), galaxies become fainter and more difficult to see. So Delubac’s team had to make use of the structure of distant intergalactic hydrogen gas to measure the baryon acoustic oscillations.
The gas is impossible to see directly, but quasars — brilliant galactic centers fueled by supermassive black holes rapidly accreting material — illuminate the otherwise invisible matter. Any intervening clouds of hydrogen gas will leave dark lines in the quasar’s spectrum.
Detailed measurements of multiple quasars’ spectra close together can actually reveal the 3-dimensional nature of the intervening hydrogen clouds. From these maps, astronomers can extract the baryon acoustic oscillation signature.
"Three years ago BOSS used 14,000 quasars to demonstrate we could make the biggest 3-D maps of the universe," says David Schlegel (Lawrence Berkeley National Lab), principal investigator of BOSS. "Two years ago, with 48,000 quasars, we first detected baryon acoustic oscillations in these maps. Now, with more than 150,000 quasars, we've made extremely precise measures of baryon acoustic oscillations.”
By probing the Hubble parameter at such an early epoch, BOSS has measured a key anchor in the early universe when dark energy had yet to take hold. By comparing the parameter throughout cosmic history, astronomers will better determine the exact nature of the elusive energy that has mysteriously caused the expansion of our universe to speed up over the last 6 billion years.
Andreu Font-Ribera et al. “Quasar-Lyman α Forest Cross-Correlation from BOSS DR11: Baryon Acoustic Oscillations” Journal of Cosmology and Astropartical Physics, 2014
Timothée Delubac et al. “Baryon Acoustic Oscillations in the Lyα forest of BOSS DR11 quasars” Astronomy & Astrophysics, 2014 | 0.849308 | 4.16865 |
Researchers have uncovered what they say is a new class of ultra-low-density ice, which crystallises amid extreme negative pressure on water molecules.
While many of us are only familiar with the kind of frozen water that keeps our drinks nice and chilled, regular ice on Earth is just one of around 20 known phases of ice – and the new forms discovered by researchers in Japan appear to have the lowest density of all known ice crystals.
The new ice is called aeroice, and its discovery by researchers at Okayama University is part of an emerging wave of research into how water freezes.
A lot of previous studies have seen huge amounts of pressure applied to water molecules to create kinds of ultra-dense ice that don't naturally occur on Earth under ordinary atmospheric conditions, but here the team was focussed on the opposite cause and effect – the absence of pressure to make ice that isn't dense.
"Our research, which surveys an entire negative-pressure region for the first time, provides a significant stepping stone in exploring this vast and intricate territory on the phase diagram," says lead researcher Masakazu Matsumoto.
As it stands, there are 17 recognised solid crystalline phases of water that can form all different kinds of ice. Of these, only two occur naturally on Earth, hexagonal ice and cubic ice.
It's the former, known as Ice Ih, that makes up almost all the ice on our planet, but another type called Ice Ic can form in Earth's upper atmosphere.
All the other kinds of ice phases are what happens when water molecules are frozen in extreme conditions – often involving severe variations in pressure to replicate how ice might form in exotic or far-flung environments, such as when icy planetary bodies collide in space.
Anyway, of the 17 known ice phases – which are named in order of their discovery – only two have lower density than normal ice. These are the latest additions to the lineup, called Ice XVI and Ice XVII.
In the right conditions, this frozen cage could take shape around a guest molecule – in this case, neon atoms – which could then be extracted from the structure, resulting in what became the lowest density phase of ice yet discovered.
Above, you can see an example of zeolitic ice on the left, with the molecular structure of one of the types of aeroice on the right.
Not to be outdone by Ice XVI, simulations by another team of researchers surpassed the milestone in 2016 with Ice XVII, using a similar molecule trapping-and-extracting technique, that theoretically results in ice with 25 percent less density than Ice XVI.
The new discovery by Matsumoto's team, aeroice, again stems from molecular rearrangements conducted at negative pressure, but this time involving silica (aka silicon dioxide, SiO2).
In simulations, the team removed the two oxygen atoms from SiO2 molecular structure and then swapped out each molecule's single silicon atom for a single oxygen atom, before adding hydrogen atoms.
The end result produces a kind of ice with a density about half that of liquid water (~0.5 g/cm3), but despite that extreme low-density, the researchers say aeroices are more stable than any other kinds of zeolite ice that have been engineered to date.
Additional simulations suggest aeroices could become even less dense – between 0 and 0.5 grams per cubic centimetre – with additional tampering.
By adding polyhedral building blocks (structures with six planes or more), the molecules could maintain their crystalline stability while making the overall structure sparser, which would lower the density – meaning any number of aeroices could ultimately be possible.
"Ices with lower density than normal ice are also found to be manifold," says Matsumoto.
"These new structures are the aeroices, and they can be more stable than any zeolitic ice at certain thermodynamic conditions under negative pressure."
While the findings may be largely of academic interest right now, the potential applications of discoveries like this are huge, ranging from understanding how water behaves in nanotubes and nanopores, to discovering how ice might behave for off-world colonists exploring the far reaches of the Solar System.
That's a lot to think about, sure, and it'd probably go down better with a cool beverage in your hand.
The findings are reported in The Journal of Chemical Physics. | 0.830061 | 3.812711 |
NASA captures 3D video of comet plunging into sun
NASA's twin sun-watching STEREO spacecrafts have tracked a comet as it looped around the sun before impact.
A comet plunging into the sun has been captured in 3-D as it hurtled along its kamikaze path for the first time, solar physicists announced Monday.
Four post-doctoral researchers at UC Berkeley's Space Science's Laboratory used instruments aboard NASA's Solar Terrestrial Relations Observatory (STEREO) spacecraft to track the so-called sun-grazing comet as it approached the sun. They were able to estimate an approximate time and place of impact.
NASA's STEREO mission, which launched in 2006, is actually made up of twin spacecraft that orbit the sun, one ahead of the Earth and one behind it, and provide stereo views of the sun.
Close to the sun
Sun-grazing comets are made up of dust, rock and ice. These comets are rarely tracked as they speed toward the sun because their brightness is overwhelmed by the solar disk.
But every now and then, a comet stands out in views from sun-watching spacecraft like STEREO and the Solar and Heliospheric Observatory (SOHO).
The comet seen by Raftery and her fellow researchers apparently survived the intense heat of the sun's outer atmosphere – called the corona – and disappeared in the chromosphere, which is a thin layer of plasma found between the visible surface of the sun and the corona.
The comet eventually evaporated in the scorching heat that reaches almost 180,000 degrees Fahrenheit (close to 100,000 degrees Celsius).
Raftery and her colleagues, Juan Carlos Martinez-Oliveros, Samuel Krucker and Pascal Saint-Hillaire, concluded that the comet was probably from the Kreutz family of comets, a group of Trojan or Greek comets that were ejected from their orbit in 2004 by the gas giant Jupiter.
The researchers also concluded that the sun-grazing comet made its first and only loop around the sun before crashing and burning.
The research team presented their findings today at the 216th meeting of the American Astronomical Society.
Tracking a comet
The comet first caught Martinez-Oliveros' attention after it was mentioned in a summary of observations by SOHO and STEREO in March.
The comet's long, bright tail of dust and ions distinguished it as a sun-grazing comet, and assuming that it was going to loop around the sun, the researchers decided to monitor it and see whether the STEREO data were good enough to allow them to accurately calculate its trajectory.
They found that the data was so precise that they were able to chart the comet's approach for two days prior to impact.
The researchers were able to estimate the impact zone within a circle about 620 miles (1,000 km) in diameter. They then pored through online data from the Mauna Loa Solar Observatory to determine if they could spot the comet next to the sun's edge in the ultraviolet region of the spectrum.
What they found was a short trail that lasted about six minutes and was only a few thousand miles above the solar surface in the sweltering corona and chromosphere.
Since the comet had a relatively short tail – about 1.86 million miles (about 3 million km) in length – the researchers believe that the comet contained heavier elements that do not evaporate as easily.
This would also help explain how the comet was able to penetrate so deeply into the sun's chromosphere, not only surviving the extreme temperatures but the strong solar winds as well, before finally evaporating.
For their study, the team used the two coronagraphs on STEREO A and B and multiple instruments on SOHO, "demonstrating the importance of multi-view observations of non-solar phenomena," the researchers wrote in the presentation of their research.
The researchers also used data from the ground-based Mauna Loa Solar Observatory, located on the flank of the Mauna Loa volcano in Hawaii, and found images of the spot they had predicted the comet to impact at, which appeared to show a comet approaching the edge of the sun from behind the solar disk.
The members of the research team, who all normally study explosive events on the sun, said that their foray into cometary physics was unplanned.
"It was supposed to be an exercise, but it took over our lives," Raftery said. | 0.87352 | 3.621017 |
Laura Dean Bennett
If the spectacular show that the solar eclipse just put on has whetted your appetite for another astronomical extravaganza, you are in luck.
It’s nearly time for the Harvest Moon – the closest, brightest and most outrageously beautiful full moon of the year.
Usually the Harvest Moon falls in September.
The term “Harvest Moon” refers to the full moon which comes closest to the autumnal equinox.
And in case you’ve forgotten, the autumnal equinox is the date when our days officially start getting shorter.
On your calendar, if it doesn’t say “Autumnal Equinox,” it will probably say “First Day of Fall.” This year, that date is September 22.
September’s full moon will be on the night of September 6.
Oddly enough, this year, the October full moon – usually called the Hunter’s Moon – is three days closer to the autumnal equinox than the September full moon.
So, officially, the October 5 full moon will be this year’s Harvest Moon.
This only happens once or twice in a decade, and it’s happening this year. It’s like we get two Harvest moons this year.
But whether it falls in September or October, the Harvest moon is a special time.
For the few nights just before and just after the Harvest Moon, it seems like there’s a full moon every night.
Known as the “Harvest Moon Effect,” this happens because of the low angle of the moon’s orbit around the Earth.
The closeness to the horizon also causes the Harvest Moon to show off in brilliant colors – orange, yellow or even red – because of how the Earth’s atmosphere bends the light.
And while the full moon is always a favorite subject for photographers, the Harvest Moon makes for an even more magical picture.
This effect gives everyone in the Northern Hemisphere some extra evening light to work by, just when that light is needed most – for gathering crops – hence the name that the Native Americans gave it – the “Harvest Moon.”
September’s full moon was also known to Native American tribes as the “Full Corn Moon” because it corresponded with the ripening of their most important crop – corn.
It’s also been called the “Barley Moon,” the “Moon When Calves Grow Hair” and the “Moon of Scarlet Plums.”
And the “Harvest Moon” wasn’t only called that by the Native Americans and early settlers. It’s been known by that same name in many languages around the world for thousands of years.
Now, around these parts, I can tell you that for most of us, autumnal equinox or no, fall has already started.
As I’m writing this story, there are no birds singing at all.
The change is particularly noticeable as just the other day I remember mentioning that the birds woke me up with a loud and especially exuberant concert which lasted all day.
Maybe it was their way of saying goodbye to their summer home before leaving on their long migration south.
The leaves are starting to turn and a few are even drifting down from their trees.
The farmers are finishing their second cutting of hay and our apples are nearly ready for picking.
Our gardens are furiously producing – growing and ripening as fast as they can to beat the coming frosts.
The harvest is upon us.
More than likely, humans have always felt the same stirrings we feel during the change of seasons. It feels like a definite sense of urgency – time to do something.
Now, it’s time to gather your grapes, pick the last of your garden crops and flowers, cut your last hay, butcher hogs and beeves and get whatever wood you’ll need piled up near the door.
It’s soon going to be apple picking and potato digging time.
Like the animals who live around and among us, it’s time to get ready for winter.
For thousands of years, humans have counted their blessings and gathered their crops at this time of year, and sometimes, when necessary, picked, cut or dug their crops by the light of the big, bright, full moon in September.
Thankfully, native American crops became staples to early European settlers of North America, who were taught how to grow them by the indigenous people.
Probably one of the most important contributions to the settlers’ livelihood and the New World’s economy was the adoption of the Native American ways of raising their crops, chiefly tobacco and corn.
The harvests gathered by the Harvest Moon by our ancestors in these parts included beans, corn, squash, peas, okra, peppers, squash and pumpkins.
Not here in the Allegheny Mountains, but in some of the early American settlements, tobacco, rice and peanuts were also grown.
Tobacco was a valuable crop and an important export, but corn was the most essential single crop to all farmers, as it was grown all over in the New World and was used to feed both people and livestock.
But growing any crop was hard work. Before there were tractors, farming was done by hand.
Huge tracts of land had to be cleared, – by hand – of huge trees and stubborn rocks and farmed with blister-raising plows, hoes, scythes, axes and shovels.
If a frontier farmer was lucky, he would have had a horse or a mule, a willing wife, a passel of children and maybe even a willing neighbor helping him in the field.
But a really fortunate farmer would have also had a team of oxen – the 18th Century equivalent to an air conditioned John Deere.
Even before we called this time of year “September,” we knew that this was our best, and maybe, last chance to gather food for the winter before the killing frosts and freezes.
When farmers had their crops ready for harvesting, neighbors who lived close enough would sometimes come and help with the harvest.
With the weather still hospitable to being outdoors, what sometimes followed a successful harvest would be a gathering of family, friends and neighbors.
Thankful prayers to the Creator and gratitude to neighbors led to a feast of fresh food from the garden. Then the long day of harvesting would often end with fiddle music and quadrille, or “square” dancing.
Young people of courting age must have looked forward to harvest time quite keenly, as it might well have been the best time during the whole year to meet members of the opposite sex and start, or renew, a courtship.
The Harvest Moon reminds us that our time to work and play in the outdoors is coming to an end for another year.
It’s time to can the vegetables, preserve the fruit, wrap the potatoes in newspaper and store them away in the cellar, eat corn on the cob and tomato sandwiches until they come out of our ears.
It’s time to think about cleaning and storing the garden tools and planning for the fall pruning.
Today, although we certainly do gather at each other’s farms to help make hay and gather the bounty from our gardens and orchards, we have the luxury of celebrating the harvest in lots of other ways, too.
There are harvest fairs and festivals, square dances, corn mazes, apple butter stirrings and cider-making parties to attend.
It’s as though we go into one last joyful fling of socializing outdoors before the icy winds of winter conspire to keep us at home in front of the fire.
The Harvest Moon is the harbinger of all of that.
I am going to call the September full moon “my Harvest Moon.”
It will remind me not to tarry – to finish harvesting and canning the last of my tomatoes, get ready to pick my apples and grapes and gather the last blossoms of summer.
By the time the real Harvest Moon comes around in October, I should be well on my way to being ready for winter. The porch furniture will be put away or covered and the pruning and outside repairs will be underway before the snow flies.
With any luck, the weather will be clear on both nights – September 6 and October 5 – and I’ll be able to enjoy sitting outside by the fire, watching a big, bright Harvest Moon – twice.
The seasons change, and we must change with them.
Isn’t it wonderful? | 0.822309 | 3.325204 |
eso0025 — Photo Release
ESO Observations of New Moon of Jupiter
4 August 2000
Two astronomers, both specialists in minor bodies in the solar system, have performed observations with ESO telescopes that provide important information about a small moon, recently discovered in orbit around the solar system's largest planet, Jupiter. Brett Gladman (of the Centre National de la Recherche Scientifique (CNRS) and working at Observatoire de la Cote d'Azur, France) and Hermann Boehnhardt (ESO-Paranal) obtained detailed data on the object S/1999 J 1, definitively confirming it as a natural satellite of Jupiter. Seventeen Jovian moons are now known.
The S/1999 J 1 object
On July 20, 2000, the Minor Planet Center (MPC) of the International Astronomical Union (IAU) announced on IAU Circular 7460 that orbital computations had shown a small moving object, first seen in the sky in 1999, to be a new candidate satellite of Jupiter.
The conclusion was based on several positional observations of that object made in October and November 1999 with the Spacewatch Telescope of the University of Arizona (USA). In particular, the object's motion in the sky was compatible with that of an object in orbit around Jupiter. Following the official IAU procedure, the IAU Central Bureau for Astronomical Telegrams designated the new object as S/1999 J 1 (the 1st candidate Satellite of Jupiter to be discovered in 1999).
Details about the exciting detective story of this object's discovery can be found in an MPC press release and the corresponding Spacewatch News Note.
Unfortunately, Jupiter and S/1999 J 1 were on the opposite side of the Sun as seen from the Earth during the spring of 2000. The faint object remained lost in the glare of the Sun in this period and, as expected, a search in July 2000 through all available astronomical data archives confirmed that it had not been seen since November 1999, nor before that time.
With time, the extrapolated sky position of S/1999 J 1 was getting progressively less accurate. New observations were thus urgently needed to "recover" this object and "secure" its orbit.
Recovery of S/1999 J 1 at La Silla
Jupiter and its moons would again become visible in the early morning hours in late July with telescopes in the southern hemisphere. By a fortunate coincidence, observing time for observations of comets and asteroids had been allocated to Brett Gladman and his collaborators at two ESO telescopes in exactly this period.
Just before sunrise on July 25, he used the Wide Field Imager (WFI) on the MPG/ESO 2.2-m telescope at La Silla to search for S/1999 J 1.
This camera has a comparatively large field-of-view, about 0.5 x 0.5 deg 2, or about the size of the full moon. This was comfortably larger than the estimated uncertainty in the object's predicted position at the time of the observation. And indeed, S/1999 J 1 was spotted not too far from that location, weakly visible in the glare of the nearby waning moon.
Detailed observations of S/1999 J 1 at Paranal
Only three days later, in the early morning hours of July 28, the small object was again imaged, this time from the 8.2-metre VLT ANTU telescope at Paranal. Brett Gladman and Hermann Boehnhardt, now knowing exactly where to look in the sky, used the FORS-1 multi-mode instrument to obtain exposures of S/1999 J 1 through several optical filters.
The great light-collecting power of this telescope resulted in excellent images while S/1999 J 1 was moving across the sky. These observations definitively confirmed the "recovery" of the object and also provided an accurate determination of its brightness and colour, cf. IAU Circular 7472, published on August 3.
From accurate positional measurements on these exposures and the earlier ones from La Silla, Gareth Williams of the Minor Planet Center was able to substantially improve the computation of the orbit of S/1999 J 1 around Jupiter. It was found (IAU Circular 7469) to move in a somewhat elliptical orbit around Jupiter with a period of just over 2 years (768 days) and at a mean distance of 24.2 million kilometres from the planet.
The nature of S/1999 J 1
This means that S/1999 J 1 belongs to the class of "irregular satellites" which move on non-circular and inclined orbits around the planet. They are believed to have been captured onto their current orbits after the planet was formed.
S/1999 J 1 is one of the outermost moons of Jupiter known so far. The eight previously-known "irregular satellites" are split into two groups of four. The four members of the more distant group (Ananke, Carme, Pasiphae and Sinope) move on retrograde orbits, i.e. clockwise as seen from above the solar system (opposite to the motion of all major planets, including the Earth). The newly improved orbit of S/1999 J 1 shows it to be a fifth member of this retrograde cluster.
The brightness of S/1999 J 1, as measured on the VLT images, indicates that it must be comparatively small, with a diameter of the order of 10 - 15 kilometres (the smallest Jovian moon known so far). However, an accurate value can only be deduced once the reflectivity of its surface is known.
The colour is very slightly red. This appears to favour the possibility that it is a captured asteroid (minor planet), rather than a cometary nucleus, but additional work is needed to cast more light on this.
When more observations of S/1999 J 1 become available, the discoverers will propose a name, from Greek mythology according to astronomical tradition, to be approved by the IAU Working Group for Planetary System Nomenclature. | 0.869623 | 3.616379 |
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