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  • 1
    Publication Date: 2012-11-07
    Description: The surface of the asteroid Vesta has prominent near-infrared absorption bands characteristic of a range of pyroxenes, confirming a direct link to the basaltic howardite-eucrite-diogenite class of meteorites. Processes active in the space environment produce 'space weathering' products that substantially weaken or mask such diagnostic absorption on airless bodies observed elsewhere, and it has long been a mystery why Vesta's absorption bands are so strong. Analyses of soil samples from both the Moon and the asteroid Itokawa determined that nanophase metallic particles (commonly nanophase iron) accumulate on the rims of regolith grains with time, accounting for an observed optical degradation. These nanophase particles, believed to be related to solar wind and micrometeoroid bombardment processes, leave unique spectroscopic signatures that can be measured remotely but require sufficient spatial resolution to discern the geologic context and history of the surface, which has not been achieved for Vesta until now. Here we report that Vesta shows its own form of space weathering, which is quite different from that of other airless bodies visited. No evidence is detected on Vesta for accumulation of lunar-like nanophase iron on regolith particles, even though distinct material exposed at several fresh craters becomes gradually masked and fades into the background as the craters age. Instead, spectroscopic data reveal that on Vesta a locally homogenized upper regolith is generated with time through small-scale mixing of diverse surface components.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pieters, C M -- Ammannito, E -- Blewett, D T -- Denevi, B W -- De Sanctis, M C -- Gaffey, M J -- Le Corre, L -- Li, J-Y -- Marchi, S -- McCord, T B -- McFadden, L A -- Mittlefehldt, D W -- Nathues, A -- Palmer, E -- Reddy, V -- Raymond, C A -- Russell, C T -- England -- Nature. 2012 Nov 1;491(7422):79-82. doi: 10.1038/nature11534.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2012-05-15
    Description: Multispectral images (0.44 to 0.98 mum) of asteroid (4) Vesta obtained by the Dawn Framing Cameras reveal global color variations that uncover and help understand the north-south hemispherical dichotomy. The signature of deep lithologies excavated during the formation of the Rheasilvia basin on the south pole has been preserved on the surface. Color variations (band depth, spectral slope, and eucrite-diogenite abundance) clearly correlate with distinct compositional units. Vesta displays the greatest variation of geometric albedo (0.10 to 0.67) of any asteroid yet observed. Four distinct color units are recognized that chronicle processes--including impact excavation, mass wasting, and space weathering--that shaped the asteroid's surface. Vesta's color and photometric diversity are indicative of its status as a preserved, differentiated protoplanet.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Reddy, Vishnu -- Nathues, Andreas -- Le Corre, Lucille -- Sierks, Holger -- Li, Jian-Yang -- Gaskell, Robert -- McCoy, Timothy -- Beck, Andrew W -- Schroder, Stefan E -- Pieters, Carle M -- Becker, Kris J -- Buratti, Bonnie J -- Denevi, Brett -- Blewett, David T -- Christensen, Ulrich -- Gaffey, Michael J -- Gutierrez-Marques, Pablo -- Hicks, Michael -- Keller, Horst Uwe -- Maue, Thorsten -- Mottola, Stefano -- McFadden, Lucy A -- McSween, Harry Y -- Mittlefehldt, David -- O'Brien, David P -- Raymond, Carol -- Russell, Christopher -- New York, N.Y. -- Science. 2012 May 11;336(6082):700-4. doi: 10.1126/science.1219088.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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