Using data from the Diviner Lunar Radiometer, an instrument uniquely capable of identifying common lunar silicate minerals, scientists at Stony Brook University in New York and NASA’s Jet Propulsion Laboratory have found previously unseen compositional differences in the crustal highlands of the Moon, and have confirmed the presence of anomalously silica-rich material in five distinct regions.
Diviner data superimposed on a Lunar Orbiter IV mosaic of Aristarchus crater. Red and orange colors indicate silicic compositions. “In layman’s terms, we have discovered a new and fundamentally different type of rock on the Moon,” declares Dr. Timothy Glotch, assistant professor in the Department of Geosciences at Stony Brook and lead author of one of two papers on the research in this week’s issue of Science. “For decades, we’ve recognized that these spots in the crustal highlands of the Moon are different. Now we have the evidence. The Moon is more geologically complex than previously thought, and we now have to refine our ideas about its formation.”
Every mineral, and therefore every rock, absorbs and emits energy with a unique spectral signature that can be measured to reveal its identity. For the first time, the Diviner Lunar Radiometer is providing scientists with global, high-resolution infrared maps of the Moon, which are enabling them to make a definitive identification of silicates commonly found within its crust.
“Diviner is literally viewing the Moon in a whole new light,” says Dr. Benjamin Greenhagen of NASA’s Jet Propulsion Laboratory, lead author of the other paper. Lunar geology can be roughly broken down into two categories – the anorthositic highlands, rich in calcium and aluminum, and the basaltic maria, which are abundant in iron and magnesium. Both of these crustal rocks are what’s deemed by geologists as ‘primitive’; that is, they are the direct result of crystallization from lunar mantle material.
Diviner’s observations have confirmed that most lunar terrains have spectral signatures consistent with compositions that fall into these two broad categories. However, they have also revealed that the lunar highlands may be less homogenous than previously thought.
In a wide range of terrains, Diviner revealed the presence of lunar soils with compositions more sodium rich than that of the typical anorthosite crust. The widespread nature of these soils reveals that there may have been variations in the chemistry and cooling rate of the magma ocean which formed the early lunar crust, or they could be the result of secondary processing of the early lunar crust.
Most impressively, in several locations around the Moon, Diviner has detected the presence of highly silicic minerals such as quartz, potassium-rich, and sodium-rich feldspar – minerals that are only ever found in association with highly evolved lithologies (rocks that have undergone extensive magmatic processing).
The detection of silicic minerals at these locations is a significant finding for scientists, as they occur in areas previously shown to exhibit anomalously high abundances of the element thorium, another proxy for highly evolved lithologies.
“The silicic features we’ve found on the Moon are fundamentally different from the more typical basaltic mare and anorthositic highlands,” says Dr. Glotch. “The fact that we see this composition in multiple geologic settings suggests that there may have been multiple processes producing these rocks.”
Some of the silicic features, such as the Gruithiusen Domes, possess steep slopes and rough surfaces suggesting that they may be lava domes created by the slow extrusion of viscous lava on the lunar surface (similar to the dome which formed on Mt. St. Helens after its eruption).
In other regions, such as Aristarchus, the silicic spectral signatures are confined to impact craters and their ejecta blankets. This suggests that excavation of the subsurface caused by these impacts has exposed portions of plutons, which are magmas bodies that solidified underground before reaching the surface.
So how did such highly silicic lithology form on a Moon that is dominated by calcium-rich anorthosite highlands, and iron and magnesium-rich basaltic maria?
Most of the locations occur in the Procellarum KREEP Terrane (PKT), an area on the lunar nearside known for its extensive basaltic volcanism. This has led scientists to believe that the silica-rich material present in this region is a result of hot basaltic magma intruding into and remelting the lunar crust.
However, one of the regions, Compton Belkovich, occurs on the far-side of the Moon, far from the PKT and its associated volcanism. The location of the Compton Belkovich anomaly suggests that the conditions that led to sustained heat production and volcanism within the PKT may have been present at much smaller scales on the far side of the Moon.
One thing not apparent in the data is evidence for pristine lunar mantle material, which previous studies have suggested may be exposed at some places on the lunar surface. Such material, rich in iron and magnesium, would be readily detected by Diviner.
However, even in the South Pole Aitken Basin (SPA), the largest, oldest, and deepest impact crater on the Moon – deep enough to have penetrated through the crust and into the mantle – there is no evidence of mantle material.
The implications of this are as yet unknown – perhaps there are no such exposures of mantle material, or maybe they occur in areas too small for Diviner to detect.
However it’s likely that if the impact that formed this crater did excavate any mantle material, it has since been mixed with crustal material from later impacts inside and outside SPA. “The new Diviner data will help in selecting the appropriate landing sites for future missions to return samples from SPA. We want to use these samples to date the SPA-forming impact and potentially study the lunar mantle, so it’s important to use Diviner data to identify areas with minimal mixing. ” says Greenhagen.
The Diviner Lunar Radiometer will continue to provide detailed infrared and solar reflectance maps of the Moon for the remainder of the LRO mission.
Kutumia data kutoka kwa Diviner Lunar Radiometer, chombo cha pekee kinachoweza kutambua madini ya kawaida ya silika ya mwezi, wanasayansi wa Chuo Kikuu cha Stony Brook huko New York na Maabara ya Jet Propulsion ya NASA wamegundua tofauti za awali za muundo katika nyanda za juu za udongo wa Mwezi, na wamethibitisha uwepo wa nyenzo isiyo ya kawaida yenye silika katika mikoa mitano tofauti. Takwimu za mtafiti wa sayari zimewekwa juu ya mchoro wa Mwezi wa Mzunguko wa IV wa kreta ya Aristarchus. Rangi nyekundu na ya machungwa huonyesha muundo wa silisi. "Kwa maneno ya kawaida, tumegundua aina mpya na tofauti ya mwamba kwenye Mwezi,"" anasema Dk Timothy Glotch, profesa msaidizi katika Idara ya Sayansi ya Dunia katika Chuo Kikuu cha Stony Brook na mwandishi mkuu wa moja ya karatasi mbili juu ya utafiti katika toleo la wiki hii la Sayansi." Kwa miongo mingi, tumetambua kwamba sehemu hizi katika nyanda za juu za mwezi ni tofauti. Sasa tuna uthibitisho. Mwezi ni ngumu zaidi ya kijiolojia kuliko tulivyofikiri hapo awali, na sasa tunapaswa kusafisha mawazo yetu juu ya kuundwa kwake. kila madini, na kwa hiyo kila mwamba, huchukua na kutoa nishati na saini ya kipekee ya spectral ambayo inaweza kupimwa ili kufunua utambulisho wake. Kwa mara ya kwanza, Devin Lunar Radiometer inatoa wanasayansi ramani za ulimwengu za infrared za mwezi, ambazo zinawawezesha kufanya utambulisho wa mwisho wa silicate zinazopatikana ndani ya ganda lake. "Diviner ni kihalisi kuangalia Mwezi katika mwanga mpya kabisa", anasema Daktari Benjamin Greenhagen wa NASA's Jet Propulsion Laboratory, mwandishi mkuu wa karatasi nyingine. Jiolojia ya mwezi inaweza kugawanywa katika makundi mawili - maeneo ya juu ya anorthositic, yenye utajiri wa kalsiamu na alumini, na maria ya basaltic, ambayo ni ya wingi katika chuma na magnesiamu. Miamba hii miwili ya ganda ni kile kinachochukuliwa na wanjiolojia kama "ya awali"; ambayo ni, ni matokeo ya moja kwa moja ya crystallization kutoka kwa nyenzo ya mantle ya mwezi. Uchunguzi wa Diviner umethibitisha kwamba maeneo mengi ya mwezi yana saini za spectral zinazolingana na muundo ambao huanguka katika makundi haya mawili makubwa. Hata hivyo, wamefunua pia kwamba huenda maeneo ya juu ya mwezi hayakuwa sawa kama ilivyodhaniwa hapo awali. Katika maeneo mbalimbali, Diviner alifunua uwepo wa udongo wa mwezi wenye muundo wenye sodiamu nyingi kuliko ule wa tabaka la kawaida la anorthosite. Uwezo wa mchanga wa kuenea kwa kiasi kikubwa unaonyesha kwamba kuna uwezekano wa kuwa na tofauti katika kemikali na kiwango cha baridi ya bahari ya magma ambayo iliunda ganda la mwezi la mapema, au inaweza kuwa matokeo ya usindikaji wa sekondari wa ganda la mwezi la mapema. Katika maeneo kadhaa karibu na Mwezi, Diviner imegundua uwepo wa madini ya silicon kama vile quartz, potasiamu-tajiri, na sodiamu-tajiri feldspar, ambayo hupatikana tu katika ushirika na lithologies ya juu (miamba ambayo imepitia usindikaji mkubwa wa magmatic). Ugunduzi wa madini ya silicic katika maeneo haya ni ugunduzi muhimu kwa wanasayansi, kwani hutokea katika maeneo ambayo hapo awali yalionyeshwa kuwa na wingi wa juu wa thorium, proxy nyingine ya lithologies ya hali ya juu. "Vipengele vya silicic tulivyogundua kwenye Mwezi ni tofauti kabisa na mare ya kawaida ya basaltic na milima ya anorthositic", anasema Dk. Glotch. "Ukweli kwamba tunaona muundo huu katika mazingira mbalimbali ya kijiolojia unaonyesha kwamba kunaweza kuwa na michakato mbalimbali ya kuzalisha miamba hii. "" Baadhi ya vipengele vya silicic, kama vile Gruithiusen domes, zina mteremko mkali na nyuso mbaya zinazoonyesha kwamba wanaweza kuwa lava domes kuundwa na extrusion polepole ya lava viscous juu ya uso wa mwezi (kama vile dome ambayo iliundwa juu ya Mt." St. Helens baada ya mlipuko wake). Katika maeneo mengine, kama vile Aristarchus, saini za spectral za silicic zimepunguzwa kwa milipuko ya athari na blanketi zao za ejecta. Hii inaonyesha kwamba kuchimba chini ya ardhi kusababishwa na athari hizi imefunua sehemu za plutoni, ambayo ni miili ya magma ambayo ilijenga chini ya ardhi kabla ya kufikia uso. Kwa hiyo, ni kwa nini kuna miamba ya silika kwenye Mwezi ambao ina mchanga wenye madini mengi ya chuma na magnesiamu? Mimea hiyo inaishi katika eneo la Procellarum Kreepa Terrane (PKT), eneo la karibu na mwezi linalojulikana kwa volkano yake ya basaltic. Kwa sababu hiyo, wanasayansi wanaamini kwamba madini hayo yenye silika ni matokeo ya magma yenye joto ya basalti ambayo iliingia ndani ya tabaka la mwezi na kuyeyusha tena. Mji huo unaitwa Compton-Belkovich na unapatikana upande wa mbali wa mwezi, mbali na eneo la volkano la Pictet. Anomali ya Compton-Belkovich inaonyesha kwamba hali zilizosababisha uzalishaji wa joto na volkano ndani ya PGT zinaweza kuwa zipo kwa kiwango kidogo zaidi upande wa mbali wa Mwezi. "Jambo moja ambalo halionekani katika data ni ushahidi wa nyenzo ya ""mashimo"" ya mwezi, ambayo masomo ya awali yamedokeza inaweza kuwa wazi katika maeneo fulani kwenye uso wa mwezi." Vitu hivyo, vyenye madini mengi ya chuma na magnesiamu, vingeweza kugunduliwa kwa urahisi na Diviner. Hata hivyo, hata katika South Pole Aitken Basin (SPA), kubwa, ya zamani, na ya kina athari crater juu ya Mwezi - kina kutosha kuwa kupenya kupitia udongo na katika mantle - hakuna ushahidi wa nyenzo mantle. Matokeo ya hili bado hayajulikani - labda hakuna mfiduo kama huo wa nyenzo ya mantle, au labda hutokea katika maeneo madogo sana kwa Diviner kugundua. Hata hivyo, ni uwezekano kwamba ikiwa mgongano uliounda kreta hii ulichimba nyenzo yoyote ya mantle, tangu wakati huo imechanganywa na nyenzo ya crustal kutoka kwa athari za baadaye ndani na nje ya SPA. Takwimu mpya za Diviner zitasaidia katika kuchagua maeneo sahihi ya kutua kwa misheni za baadaye kurudisha sampuli kutoka SPA. """Tunataka kutumia sampuli hizi tarehe SPA-kuunda athari na uwezekano wa kujifunza mantle mwezi, hivyo ni muhimu kutumia Diviner data kutambua maeneo na mchanganyiko mdogo." <unk> anasema Greenhagen. Diviner Lunar Radiometer itaendelea kutoa ramani za kina za infrared na mwangaza wa jua wa Mwezi kwa kipindi kilichobaki cha ujumbe wa LRO.