The Gaia mission, scheduled to launch Thursday morning (Dec. 19), could be a bonanza for discovering exoplanets, perhaps finding more than 2,500 new alien worlds, scientists suggest. 
 
 Gaia, a $1 billion (740 million euros) mission from the European Space Agency (ESA), aims to chart a 3D map of the Milky Way by surveying more than 1 billion stars, amounting to about 1 percent of the stars in the galaxy, using its billion-pixel camera. Its goal is to make the largest, most precise map of where Earth dwells by observing the position of each of these stars 70 times over five years. 
 
 ESA will broadcast a live webcast of Gaia's launch atop a Russian Soyuz rocket from the Guiana Space Center in South America beginning at 3:30 a.m. EST (0830 GMT) on Thursday. Gaia is scheduled to launch at 4:12 a.m. EST (0912 GMT), and you can watch the Gaia webcast live on SPACE.com, courtesy of ESA. [See photos of the Gaia spacecraft] 
 
 To pinpoint the position of a star in 3D — a field known as astrometry — Gaia will measure the distance of the star from the sun. The satellite will do so by watching how its position shifts over time. As the Earth orbits the sun, the apparent positions of stars change with regard to each other due to how our viewpoint has moved, a phenomenon known as parallax. 
 
 Discovering a star's distance can narrow down many of its other details. For instance, the actual brightness of a star can only be determined by not only measuring how bright it appears but also how far away it lies and thus how distance might have dimmed its light. Once researchers know how bright a star actually is, they can determine how much fuel it must burn — that is, the star's mass. A star's brightness is also related to its width, and so discovering its brightness can help deduce its size. Knowing a star's mass and size then helps determine the strength of gravity on its surface. 
 
 Gaia will also scan the color of stars. This can help reveal details of their chemical makeup as well as its temperature, as the color of a star depends on its surface temperature. Knowing the brightness and color of a star can also help figure out its age and thus stage in its evolution. All in all, Gaia will help shed light on the composition, formation and evolution of the stars that make up the galaxy, researchers say. 
 
 Gaia will make the largest, most precise 3D map of our galaxy by surveying an unprecedented number of stars. Credit: ESA 
 
 Charting the stars and planets 
 
 Gaia is not the first space mission to chart the stars. In 1989, ESA launched the Hipparcos satellite, which charted the positions of more than 100,000 stars with high precision and more than 2 million stars with slightly less precision. In the end, Hipparcos measured the distances of all stars within 325 light-years and bright stars within 3,250 light-years (to within 10 percent). 
 
 In comparison, Gaia will collect more than 30 times more light than Hipparcos. This will help measure a star's position 200 times more accurately. All in all, Gaia can measure the distances of stars as far away as the galactic center — roughly 32,500 light-years away — with an accuracy within 10 percent. 
 
 On top of what light Gaia might shed on the stars in the Milky Way, it may also reveal exoplanets orbiting them, said astronomer Alessandro Sozzetti at the Astrophysical Observatory of Turin in Italy. This could be the first time exoplanets are detected using astrometry. [Video: Galaxy's Most Precise 3D Map: Gaia Probe Will Make It] 
 
 NASA's exoplanet-hunting Kepler spacecraft discovered planets through photometry — that is, by measuring light. It looked at regular dips in starlight caused by planets crossing between stars and Earth. 
 
 Gaia can hunt worlds a different way. The gravitational pull of a planet can introduce a regular wobble in its host star's position as they orbit each other that Gaia can detect over time. 
 
 Gaia will be most effective at detecting giant planets orbiting small stars. These planetary systems are prone to generating significant, noticeable wobbles in a star's position. 
 
 Sozzetti and his colleagues focused on red dwarfs, also known as M dwarf stars, which are relatively small, less than 60 percent the mass of the sun. These stars make up roughly three-quarters of the stars in the galaxy, and scientists recently found red dwarfs are far more common than before thought, making up at least 80 percent of the total number of stars. Moreover, past research suggests about 6.5 percent of red dwarfs host giant Jupiter-mass planets. 
 
 The researchers devised computer models simulating Jupiter-mass planets around the 3,150 red dwarfs known to exist within about 110 light-years of Earth. They estimated Gaia could detect about 100 new giant planets from this sample if such worlds exist about 0.5 to 3 astronomical units around those stars. (An astronomical unit is equal to Earth's distance from the sun — about 93 million miles, or 150 million kilometers.) 
 
 In addition, unlike Kepler, Gaia should be able to deduce the full orbits and masses of these giant worlds. For more than 80 percent of stars detected by Gaia around M dwarf stars within about 110 light-years of Earth, their masses could be measured to within 10 percent. 
 
 Extrapolating from these findings, the researchers suggest Gaia could find about 2,600 giant planets orbiting the roughly 415,000 red dwarfs within about 325 light-years from Earth. [The Strangest Alien Planets (Photos)] 
 
 Sozzetti and his colleagues detailed their findings online Nov. 11 in the journal Monthly Notices of the Royal Astronomical Society. 
 
 "Gaia should be able to detect orbital motion for giant planets orbiting hundreds of M dwarfs," said astronomer David Latham at the Harvard-Smithsonian Center for Astrophysics, who did not take part in this study. 
 
 The researchers also calculated they could accurately derive the masses and orbits of as many as 500 of these 2,600 planets. In addition, within this group of stars, Gaia might identify hints of 10 systems with planets that might possibly noticeably cross in front of their host stars. 
 
 Exoplanet astrometry 
 
 Astronomers have tried detecting exoplanets using astrometry before. Until now, astrometry has only helped confirm the existence of exoplanets detected through other methods, not ones astrometry spotted directly. So far astrometry has suffered about 70 years of blunders in the field of exoplanet detection, "with many a discovery announcement biting the dust," Sozzetti said. "We're finally on the verge of seeing astrometry coming of age and providing substantial contributions to this field." 
 
 Sozzetti cautioned that Gaia is not sensitive enough to detect planets of about Earth's mass, as Kepler is. "Its astrometric accuracy is not sufficient, not even for the nearest stars," he said. 
 
 Gaia should also not be able to detect planets within the habitable zones of red dwarfs — that is, the areas around stars where it is warm enough on a planet's surface for water to stay liquid. Since red dwarfs are very dim, their habitable zones are typically very close to them, about 3 percent to 30 percent of an astronomical unit. The astrometric signals caused by planets get increasingly smaller the closer they are to their stars, meaning that worlds in a red dwarf's habitable zone would probably be too difficult to detect. 
 
 However, Sozzetti said Gaia could provide unique insights "on the existence of systems in which the likelihood of a potentially habitable terrestrial planet may have formed is high." By seeing where a giant planet is orbiting a star, Gaia can help rule out any systems where giant planets may have interfered with the formation of rocky planets within those stars' habitable zones. 
 
 Sozzetti noted that Gaia and Kepler ought to be highly complementary in several ways. While Kepler can discover many small worlds, Gaia can find thousands of giant planets. 
 
 "The combination of Gaia and Kepler data will allow for a much improved understanding of planetary systems' properties and frequencies as a function of the host stars' characteristics," Sozzetti said. 
 
 This story was provided by Astrobiology Magazine, a web-based publication sponsored by the NASA astrobiology program. 
 
 Follow us @Spacedotcom, Facebook and Google+. Article on SPACE.com. ||||| Media playback is unsupported on your device Media caption Launch of the Gaia satellite from Sinnamary in French Guiana 
 
 Europe has launched the Gaia satellite - one of the most ambitious space missions in history. 
 
 The 740m-euro (£620m) observatory lifted off from the Sinnamary complex in French Guiana at 06:12 local time (09:12 GMT). 
 
 Gaia is going to map the precise positions and distances to more than a billion stars. 
 
 This should give us the first realistic picture of how our Milky Way galaxy is constructed. 
 
 Gaia's remarkable sensitivity will lead also to the detection of many thousands of previously unseen objects, including new planets and asteroids. 
 
 It will allow us, for the first time ever, to walk through the Milky Way - to say where everything is, to say what everything is Prof Gerry Gilmore, Cambridge University 
 
 Separation from the Soyuz upper-stage was confirmed just before 10:00 GMT. 
 
 The satellite is now travelling out to an observing station some 1.5 million km from the Earth on its nightside - a journey that will take about a month to complete. 
 
 Gaia has been in development for more than 20 years. 
 
 It will be engaged in what is termed astrometry - the science of mapping the locations and movements of celestial objects. 
 
 To do this, it carries two telescopes that throw light on to a huge, one-billion-pixel camera detector connected to a trio of instruments. 
 
 Gaia will use this ultra-stable and supersensitive optical equipment to pinpoint its sample of stars with extraordinary confidence. 
 
 Gaia - The discovery machine 
 
 Gaia will make a very precise 3D map of our Milky Way Galaxy 
 
 It is the successor to the Hipparcos satellite which mapped some 100,000 stars 
 
 The one billion to be catalogued by Gaia is still only 1% of the Milky Way's total 
 
 But the survey's quality promises a raft of discoveries beyond just the star map 
 
 It will find new asteroids and planets; It will test physical constants and theories 
 
 Gaia's sky map will be the reference to guide future telescopes' observations 
 
 By repeatedly viewing its targets over five years, it should get to know the brightest stars' coordinates down to an error of just seven micro-arcseconds. 
 
 "This angle is equivalent to the size of a euro coin on the Moon as seen from Earth," explained Prof Alvaro Gimenez, Esa's director of science. 
 
 Gaia will compile profiles on the stars it sees. 
 
 As well as working out how far away they are, the satellite will study their motion across the sky. 
 
 Their physical properties will also be catalogued - details such as brightness, temperature, and composition. It should even be possible then to determine their ages. 
 
 And for about 150 million of these stars, Gaia will measure their velocity either towards or away from us. 
 
 This will enable scientists to use them as three-dimensional markers to trace the evolution of the Milky Way, to in essence make a time-lapse movie that can be run forwards to see what happens in the future, or run backwards to reveal how the galaxy was assembled in the past. 
 
 And because Gaia will track anything that passes across its camera detector, it is likely also to see a colossal number of objects that have hitherto gone unrecorded - such as comets, asteroids, planets beyond our Solar System, cold dead stars, and even tepid stars that never quite fired into life. 
 
 "It will allow us, for the first time ever, to walk through the Milky Way - to say where everything is, to say what everything is. It is truly a transformative mission," said Prof Gerry Gilmore from Cambridge University, UK. 
 
 By the end of the decade, the Gaia archive of processed data is expected to exceed 1 Petabyte (1 million Gigabytes), equivalent to about 200,000 DVDs of information. 
 
 This store is so vast that it will keep professional astronomers busy for decades. 
 
 "To think that you see individual scientific papers coming out now that talk about just a single object - a single star or exoplanet. And very soon, because of Gaia, we will have information on a billion objects. What will the scientific literature look like then?" pondered Dr Michael Perryman, the former Gaia Esa project scientist now affiliated to Princeton University, US. 
 
 "Of course, there will be big statistical projects you can tackle with this data, but it is clear the scale of Gaia means this information is not going to be superseded for a very long time," he told BBC News. 
 
 As the Earth goes around the Sun, relatively nearby stars appear to move against the 'fixed' stars that are even further away 
 
 Because we know the Sun-Earth distance, we can use the parallax angle to work out the distance to the target star 
 
 But such angles are very small - less than one arcsecond for the nearest stars, or 0.05% of the full Moon's diameter 
 
 Gaia will make repeat observations to reduce measurement errors down to seven micro-arcseconds for the very brightest stars 
 
 Parallaxes are used to anchor other, more indirect techniques on the 'ladder' deployed to measure the most far-flung distances 
 
 It will though offer ample scope for citizen scientists to mine Gaia's data to make their own discoveries, and a number of crowdsourcing projects to facilitate this activity will get under way next year. 
 
 Gaia is the result of an enormous industrial effort led by Astrium satellites in Toulouse, France. "For this masterpiece, for this jewel of space hardware, Astrium gathered and led an industrial consortium made up of 50 companies - 47 European, three North American," said CEO Eric Beranger. 
 
 "Coming to [French Guiana] and seeing our satellite lifting off brings me huge emotion. So much effort, dedication and ingenuity captured in just a few minutes." 
 
 Media playback is unsupported on your device Media caption Jon Kemp from e2v - the UK company that produced Gaia's camera detector - explains how it works 
 
 Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos
– While you were sleeping, a truly massive undertaking got under way, one that the BBC terms "one of the most ambitious space missions in history." Europe's Gaia satellite—which has been two decades in the making—launched at 4:12am EST today, setting it on a course to essentially inventory the Milky Way and create a 3D map of it, reports Space.com. The satellite will be tasked with logging the positions and distances to some 1 billion stars—that's 1% of the stars in the galaxy—but it's expected to turn up much more. Its sophisticated instruments (among them, a 1 billion-pixel camera) should facilitate the discovery of unknown asteroids, comets, dead stars, and even planets, reports the BBC. The end result: The most realistic understanding yet of how the Milky Way was assembled. The European Space Agency describes the process: Each star will be reviewed an average 70 times over a five-year period, with Gaia measuring the distance of the star from the sun (along with properties like brightness, temperature, and chemical composition) as it moves around the sun. The repeat measurements will allow Gaia to map the brightest stars' coordinates to within seven micro-arcseconds, which an ESA official describes as an angle "equivalent to the size of a euro coin on the Moon as seen from Earth." Space.com notes that the ESA launched a previous star-mapping mission in 1989; that satellite, Hipparcos, could measure the distances of bright stars within 3,250 light-years with a modest margin of error. Gaia will be able to measure up to 32,500 light-years away.