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  • 1
    Publication Date: 2012-11-07
    Description: Localized dark and bright materials, often with extremely different albedos, were recently found on Vesta's surface. The range of albedos is among the largest observed on Solar System rocky bodies. These dark materials, often associated with craters, appear in ejecta and crater walls, and their pyroxene absorption strengths are correlated with material brightness. It was tentatively suggested that the dark material on Vesta could be either exogenic, from carbon-rich, low-velocity impactors, or endogenic, from freshly exposed mafic material or impact melt, created or exposed by impacts. Here we report Vesta spectra and images and use them to derive and interpret the properties of the 'pure' dark and bright materials. We argue that the dark material is mainly from infall of hydrated carbonaceous material (like that found in a major class of meteorites and some comet surfaces), whereas the bright material is the uncontaminated indigenous Vesta basaltic soil. Dark material from low-albedo impactors is diffused over time through the Vestan regolith by impact mixing, creating broader, diffuse darker regions and finally Vesta's background surface material. This is consistent with howardite-eucrite-diogenite meteorites coming from Vesta.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉McCord, T B -- Li, J-Y -- Combe, J-P -- McSween, H Y -- Jaumann, R -- Reddy, V -- Tosi, F -- Williams, D A -- Blewett, D T -- Turrini, D -- Palomba, E -- Pieters, C M -- De Sanctis, M C -- Ammannito, E -- Capria, M T -- Le Corre, L -- Longobardo, A -- Nathues, A -- Mittlefehldt, D W -- Schroder, S E -- Hiesinger, H -- Beck, A W -- Capaccioni, F -- Carsenty, U -- Keller, H U -- Denevi, B W -- Sunshine, J M -- Raymond, C A -- Russell, C T -- England -- Nature. 2012 Nov 1;491(7422):83-6. doi: 10.1038/nature11561.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Bear Fight Institute, 22 Fiddler's Road, Box 667, Winthrop, Washington 98862, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23128228" 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: 2011-10-01
    Description: High-resolution images of Mercury's surface from orbit reveal that many bright deposits within impact craters exhibit fresh-appearing, irregular, shallow, rimless depressions. The depressions, or hollows, range from tens of meters to a few kilometers across, and many have high-reflectance interiors and halos. The host rocks, which are associated with crater central peaks, peak rings, floors, and walls, are interpreted to have been excavated from depth by the crater-forming process. The most likely formation mechanisms for the hollows involve recent loss of volatiles through some combination of sublimation, space weathering, outgassing, or pyroclastic volcanism. These features support the inference that Mercury's interior contains higher abundances of volatile materials than predicted by most scenarios for the formation of the solar system's innermost planet.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Blewett, David T -- Chabot, Nancy L -- Denevi, Brett W -- Ernst, Carolyn M -- Head, James W -- Izenberg, Noam R -- Murchie, Scott L -- Solomon, Sean C -- Nittler, Larry R -- McCoy, Timothy J -- Xiao, Zhiyong -- Baker, David M H -- Fassett, Caleb I -- Braden, Sarah E -- Oberst, Jurgen -- Scholten, Frank -- Preusker, Frank -- Hurwitz, Debra M -- New York, N.Y. -- Science. 2011 Sep 30;333(6051):1856-9. doi: 10.1126/science.1211681.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA. david.blewett@jhuapl.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21960626" 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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  • 3
    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. carle_pieters@brown.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23128227" 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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  • 4
    Publication Date: 2015-05-09
    Description: Magnetized rocks can record the history of the magnetic field of a planet, a key constraint for understanding its evolution. From orbital vector magnetic field measurements of Mercury taken by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft at altitudes below 150 kilometers, we have detected remanent magnetization in Mercury's crust. We infer a lower bound on the average age of magnetization of 3.7 to 3.9 billion years. Our findings indicate that a global magnetic field driven by dynamo processes in the fluid outer core operated early in Mercury's history. Ancient field strengths that range from those similar to Mercury's present dipole field to Earth-like values are consistent with the magnetic field observations and with the low iron content of Mercury's crust inferred from MESSENGER elemental composition data.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Johnson, Catherine L -- Phillips, Roger J -- Purucker, Michael E -- Anderson, Brian J -- Byrne, Paul K -- Denevi, Brett W -- Feinberg, Joshua M -- Hauck, Steven A 2nd -- Head, James W 3rd -- Korth, Haje -- James, Peter B -- Mazarico, Erwan -- Neumann, Gregory A -- Philpott, Lydia C -- Siegler, Matthew A -- Tsyganenko, Nikolai A -- Solomon, Sean C -- New York, N.Y. -- Science. 2015 May 22;348(6237):892-5. doi: 10.1126/science.aaa8720. Epub 2015 May 7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada. Planetary Science Institute, Tucson, AZ 85719, USA. cjohnson@eos.ubc.ca. ; Planetary Science Directorate, Southwest Research Institute, Boulder, CO 80302, USA. ; NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. ; The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA. ; Lunar and Planetary Institute, Houston, TX 77058, USA. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA. ; Institute for Rock Magnetism, Department of Earth Sciences, University of Minnesota, Minneapolis, MN, 55455, USA. ; Department of Earth, Environmental, and Planetary Sciences, Case Western Reserve University, Cleveland, OH, 44106, USA. ; Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA. ; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA. ; Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada. ; Planetary Science Institute, Tucson, AZ 85719, USA. Department of Earth Sciences, Southern Methodist University, Dallas, TX 75205, USA. ; Institute and Faculty of Physics, Saint Petersburg State University, Saint Petersburg, Russia. ; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25953822" 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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  • 5
    Publication Date: 2011-10-01
    Description: MESSENGER observations from Mercury orbit reveal that a large contiguous expanse of smooth plains covers much of Mercury's high northern latitudes and occupies more than 6% of the planet's surface area. These plains are smooth, embay other landforms, are distinct in color, show several flow features, and partially or completely bury impact craters, the sizes of which indicate plains thicknesses of more than 1 kilometer and multiple phases of emplacement. These characteristics, as well as associated features, interpreted to have formed by thermal erosion, indicate emplacement in a flood-basalt style, consistent with x-ray spectrometric data indicating surface compositions intermediate between those of basalts and komatiites. The plains formed after the Caloris impact basin, confirming that volcanism was a globally extensive process in Mercury's post-heavy bombardment era.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Head, James W -- Chapman, Clark R -- Strom, Robert G -- Fassett, Caleb I -- Denevi, Brett W -- Blewett, David T -- Ernst, Carolyn M -- Watters, Thomas R -- Solomon, Sean C -- Murchie, Scott L -- Prockter, Louise M -- Chabot, Nancy L -- Gillis-Davis, Jeffrey J -- Whitten, Jennifer L -- Goudge, Timothy A -- Baker, David M H -- Hurwitz, Debra M -- Ostrach, Lillian R -- Xiao, Zhiyong -- Merline, William J -- Kerber, Laura -- Dickson, James L -- Oberst, Jurgen -- Byrne, Paul K -- Klimczak, Christian -- Nittler, Larry R -- New York, N.Y. -- Science. 2011 Sep 30;333(6051):1853-6. doi: 10.1126/science.1211997.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geological Sciences, Brown University, Providence, RI 02912, USA. james_head@brown.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21960625" 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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  • 6
    Publication Date: 2012-05-15
    Description: Vesta's surface is characterized by abundant impact craters, some with preserved ejecta blankets, large troughs extending around the equatorial region, enigmatic dark material, and widespread mass wasting, but as yet an absence of volcanic features. Abundant steep slopes indicate that impact-generated surface regolith is underlain by bedrock. Dawn observations confirm the large impact basin (Rheasilvia) at Vesta's south pole and reveal evidence for an earlier, underlying large basin (Veneneia). Vesta's geology displays morphological features characteristic of the Moon and terrestrial planets as well as those of other asteroids, underscoring Vesta's unique role as a transitional solar system body.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Jaumann, R -- Williams, D A -- Buczkowski, D L -- Yingst, R A -- Preusker, F -- Hiesinger, H -- Schmedemann, N -- Kneissl, T -- Vincent, J B -- Blewett, D T -- Buratti, B J -- Carsenty, U -- Denevi, B W -- De Sanctis, M C -- Garry, W B -- Keller, H U -- Kersten, E -- Krohn, K -- Li, J-Y -- Marchi, S -- Matz, K D -- McCord, T B -- McSween, H Y -- Mest, S C -- Mittlefehldt, D W -- Mottola, S -- Nathues, A -- Neukum, G -- O'Brien, D P -- Pieters, C M -- Prettyman, T H -- Raymond, C A -- Roatsch, T -- Russell, C T -- Schenk, P -- Schmidt, B E -- Scholten, F -- Stephan, K -- Sykes, M V -- Tricarico, P -- Wagner, R -- Zuber, M T -- Sierks, H -- New York, N.Y. -- Science. 2012 May 11;336(6082):687-90. doi: 10.1126/science.1219122.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉German Aerospace Center, Institute of Planetary Research, Berlin, Germany. ralf.jaumann@dlr.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22582254" target="_blank"〉PubMed〈/a〉
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    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 7
    Publication Date: 2012-09-22
    Description: We investigated the origin of unusual pitted terrain on asteroid Vesta, revealed in images from the Dawn spacecraft. Pitted terrain is characterized by irregular rimless depressions found in and around several impact craters, with a distinct morphology not observed on other airless bodies. Similar terrain is associated with numerous martian craters, where pits are thought to form through degassing of volatile-bearing material heated by the impact. Pitted terrain on Vesta may have formed in a similar manner, which indicates that portions of the surface contain a relatively large volatile component. Exogenic materials, such as water-rich carbonaceous chondrites, may be the source of volatiles, suggesting that impactor materials are preserved locally in relatively high abundance on Vesta and that impactor composition has played an important role in shaping the asteroid's geology.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Denevi, B W -- Blewett, D T -- Buczkowski, D L -- Capaccioni, F -- Capria, M T -- De Sanctis, M C -- Garry, W B -- Gaskell, R W -- Le Corre, L -- Li, J-Y -- Marchi, S -- McCoy, T J -- Nathues, A -- O'Brien, D P -- Petro, N E -- Pieters, C M -- Preusker, F -- Raymond, C A -- Reddy, V -- Russell, C T -- Schenk, P -- Scully, J E C -- Sunshine, J M -- Tosi, F -- Williams, D A -- Wyrick, D -- New York, N.Y. -- Science. 2012 Oct 12;338(6104):246-9. doi: 10.1126/science.1225374. Epub 2012 Sep 20.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA. brett.denevi@jhuapl.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22997131" 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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