ALBERT

Description: The OSIRIS experiment onboard the Rosetta spacecraft currently orbiting comet 67P/Churyumov-Gerasimenko has yielded unprecedented views of a comet's nucleus. We present here the first ever observations of meter-scale fractures on the surface of a comet. Some of these fractures form polygonal networks. We present an initial assessment of their morphology, topology, and regional distribution. Fractures are ubiquitous on the surface of the comet's nucleus. Furthermore, they occur in various settings and show different topologies suggesting numerous formation mechanisms, which include thermal insolation weathering, orbital-induced stresses, and possibly seasonal thermal contraction. However, we conclude that thermal insolation weathering is responsible for creating most of the observed fractures based on their morphology and setting in addition to thermal models that indicate diurnal temperature ranges exceeding 200 K and thermal gradients of ~15 K/min at perihelion are possible. Finally, we suggest that fractures could be a facilitator in surface evolution and long-term erosion.

Description: Pits have been observed on many cometary nuclei mapped by spacecraft. It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments and models cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts. Alternative mechanisms like explosive activity have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov-Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply that large heterogeneities exist in the physical, structural or compositional properties of the first few hundred metres below the current nucleus surface.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Vincent, Jean-Baptiste -- Bodewits, Dennis -- Besse, Sebastien -- Sierks, Holger -- Barbieri, Cesare -- Lamy, Philippe -- Rodrigo, Rafael -- Koschny, Detlef -- Rickman, Hans -- Keller, Horst Uwe -- Agarwal, Jessica -- A'Hearn, Michael F -- Auger, Anne-Therese -- Barucci, M Antonella -- Bertaux, Jean-Loup -- Bertini, Ivano -- Capanna, Claire -- Cremonese, Gabriele -- Da Deppo, Vania -- Davidsson, Bjorn -- Debei, Stefano -- De Cecco, Mariolino -- El-Maarry, Mohamed Ramy -- Ferri, Francesca -- Fornasier, Sonia -- Fulle, Marco -- Gaskell, Robert -- Giacomini, Lorenza -- Groussin, Olivier -- Guilbert-Lepoutre, Aurelie -- Gutierrez-Marques, P -- Gutierrez, Pedro J -- Guttler, Carsten -- Hoekzema, Nick -- Hofner, Sebastian -- Hviid, Stubbe F -- Ip, Wing-Huen -- Jorda, Laurent -- Knollenberg, Jorg -- Kovacs, Gabor -- Kramm, Rainer -- Kuhrt, Ekkehard -- Kuppers, Michael -- La Forgia, Fiorangela -- Lara, Luisa M -- Lazzarin, Monica -- Lee, Vicky -- Leyrat, Cedric -- Lin, Zhong-Yi -- Lopez Moreno, Jose J -- Lowry, Stephen -- Magrin, Sara -- Maquet, Lucie -- Marchi, Simone -- Marzari, Francesco -- Massironi, Matteo -- Michalik, Harald -- Moissl, Richard -- Mottola, Stefano -- Naletto, Giampiero -- Oklay, Nilda -- Pajola, Maurizio -- Preusker, Frank -- Scholten, Frank -- Thomas, Nicolas -- Toth, Imre -- Tubiana, Cecilia -- England -- Nature. 2015 Jul 2;523(7558):63-6. doi: 10.1038/nature14564.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max-Planck-Institut fur Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Gottingen, Germany. ; University of Maryland, Department of Astronomy, College Park, Maryland 20742-2421, USA. ; Scientific Support Office, European Space Research and Technology Centre/ESA, Keplerlaan 1, Postbus 299, 2201 AZ Noordwijk ZH, The Netherlands. ; University of Padova, Department of Physics and Astronomy, Vicolo dell'Osservatorio 3, 35122 Padova, Italy. ; Laboratoire d'Astrophysique de Marseille, UMR 7326, CNRS and Aix Marseille Universite, 13388 Marseille Cedex 13, France. ; 1] Centro de Astrobiologia, CSIC-INTA, 28850 Torrejon de Ardoz, Madrid, Spain [2] International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland. ; 1] Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden [2] PAS Space Research Center, Bartycka 18A, 00716 Warszawa, Poland. ; Institut fur Geophysik und extraterrestrische Physik (IGEP), Technische Universitat Braunschweig, Mendelssohnstrasse 3, 38106 Braunschweig, Germany. ; 1] University of Maryland, Department of Astronomy, College Park, Maryland 20742-2421, USA [2] Akademie der Wissenschaften zu Gottingen and Max-Planck-Institut fur Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Gottingen, Germany. ; LESIA-Observatoire de Paris, CNRS, Universite Pierre et Marie Curie, Universite Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France. ; LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d'Alembert, 78280 Guyancourt, France. ; Centro di Ateneo di Studi ed Attivita Spaziali "Giuseppe Colombo" (CISAS), University of Padova, via Venezia 15, 35131 Padova, Italy. ; INAF, Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy. ; CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy. ; Centro de Astrobiologia, CSIC-INTA, 28850 Torrejon de Ardoz, Madrid, Spain. ; Department of Industrial Engineering, University of Padova, via Venezia 1, 35131 Padova, Italy. ; University of Trento, via Mesiano 77, 38100 Trento, Italy. ; Physikalisches Institut der Universitat Bern, Sidlerstrasse 5, 3012 Bern, Switzerland. ; INAF Osservatorio Astronomico, via Tiepolo 11, 34014 Trieste, Italy. ; Planetary Science Institute, Tucson, Arizona 85719, USA. ; Instituto de Astrofisica de Andalucia (CSIC), Glorieta de la Astronomia s/n, 18008 Granada, Spain. ; Deutsches Zentrum fur Luft- und Raumfahrt (DLR), Institut fur Planetenforschung, Rutherfordstrasse 2, 12489 Berlin, Germany. ; National Central University, Graduate Institute of Astronomy, 300 Chung-Da Rd, Chung-Li 32054, Taiwan. ; Operations Department, European Space Astronomy Centre/ESA, PO Box 78, 28691 Villanueva de la Canada, Madrid, Spain. ; The University of Kent, School of Physical Sciences, Canterbury, Kent CT2 7NZ, UK. ; University of Padova, Deptartment of Physics and Astronomy, via Marzolo 8, 35131 Padova, Italy. ; Solar System Exploration Research Virtual Institute, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, Colorado 80302, USA. ; Dipartimento di Geoscienze, University of Padova, via Giovanni Gradenigo 6, 35131 Padova, Italy. ; Institut fur Datentechnik und Kommunikationsnetze der Technische Universitat Braunschweig, Hans-Sommer-Strasse 66, 38106 Braunschweig, Germany. ; 1] Centro di Ateneo di Studi ed Attivita Spaziali "Giuseppe Colombo" (CISAS), University of Padova, via Venezia 15, 35131 Padova, Italy [2] CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy [3] University of Padova, Department of Information Engineering, via Gradenigo 6/B, 35131 Padova, Italy. ; Konkoly Observatory of the Hungarian Academy of Sciences, PO Box 67, 1525 Budapest, Hungary.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26135448" target="_blank"〉PubMed〈/a〉

Description: The factors shaping cometary nuclei are still largely unknown, but could be the result of concurrent effects of evolutionary and primordial processes. The peculiar bilobed shape of comet 67P/Churyumov-Gerasimenko may be the result of the fusion of two objects that were once separate or the result of a localized excavation by outgassing at the interface between the two lobes. Here we report that the comet's major lobe is enveloped by a nearly continuous set of strata, up to 650 metres thick, which are independent of an analogous stratified envelope on the minor lobe. Gravity vectors computed for the two lobes separately are closer to perpendicular to the strata than those calculated for the entire nucleus and adjacent to the neck separating the two lobes. Therefore comet 67P/Churyumov-Gerasimenko is an accreted body of two distinct objects with 'onion-like' stratification, which formed before they merged. We conclude that gentle, low-velocity collisions occurred between two fully formed kilometre-sized cometesimals in the early stages of the Solar System. The notable structural similarities between the two lobes of comet 67P/Churyumov-Gerasimenko indicate that the early-forming cometesimals experienced similar primordial stratified accretion, even though they formed independently.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Massironi, Matteo -- Simioni, Emanuele -- Marzari, Francesco -- Cremonese, Gabriele -- Giacomini, Lorenza -- Pajola, Maurizio -- Jorda, Laurent -- Naletto, Giampiero -- Lowry, Stephen -- El-Maarry, Mohamed Ramy -- Preusker, Frank -- Scholten, Frank -- Sierks, Holger -- Barbieri, Cesare -- Lamy, Philippe -- Rodrigo, Rafael -- Koschny, Detlef -- Rickman, Hans -- Keller, Horst Uwe -- A'Hearn, Michael F -- Agarwal, Jessica -- Auger, Anne-Therese -- Barucci, M Antonella -- Bertaux, Jean-Loup -- Bertini, Ivano -- Besse, Sebastien -- Bodewits, Dennis -- Capanna, Claire -- Da Deppo, Vania -- Davidsson, Bjorn -- Debei, Stefano -- De Cecco, Mariolino -- Ferri, Francesca -- Fornasier, Sonia -- Fulle, Marco -- Gaskell, Robert -- Groussin, Olivier -- Gutierrez, Pedro J -- Guttler, Carsten -- Hviid, Stubbe F -- Ip, Wing-Huen -- Knollenberg, Jorg -- Kovacs, Gabor -- Kramm, Rainer -- Kuhrt, Ekkehard -- Kuppers, Michael -- La Forgia, Fiorangela -- Lara, Luisa M -- Lazzarin, Monica -- Lin, Zhong-Yi -- Lopez Moreno, Jose J -- Magrin, Sara -- Michalik, Harald -- Mottola, Stefano -- Oklay, Nilda -- Pommerol, Antoine -- Thomas, Nicolas -- Tubiana, Cecilia -- Vincent, Jean-Baptiste -- England -- Nature. 2015 Oct 15;526(7573):402-5. doi: 10.1038/nature15511. Epub 2015 Sep 28.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Dipartimento di Geoscienze, University of Padova, via G. Gradenigo 6, 35131 Padova, Italy. ; Centro di Ateneo di Studi ed Attivita Spaziali "Giuseppe Colombo" (CISAS), University of Padova, via Venezia 15, 35131 Padova, Italy. ; CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy. ; University of Padova, Department of Physics and Astronomy, Vicolo dell'Osservatorio 3, 35122 Padova, Italy. ; INAF, Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy. ; Aix Marseille Universite, CNRS, LAM (Laboratoire d'Astrophysique de Marseille), UMR 7326, 38 rue Frederic Joliot-Curie, 13388 Marseille, France. ; Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy. ; The University of Kent, School of Physical Sciences, Canterbury, Kent CT2 7NZ, UK. ; Physikalisches Institut der Universitat Bern, Sidlerstrasse 5, 3012 Bern, Switzerland. ; Deutsches Zentrum fur Luft- und Raumfahrt (DLR), Institut fur Planetenforschung, Rutherfordstrasse 2, 12489 Berlin, Germany. ; Max-Planck-Institut fur Sonnensystemforschung, Justus-von-Liebig Weg 3, 37077 Gottingen, Germany. ; Centro de Astrobiologia, CSIC-INTA, 28850 Torrejon de Ardoz, Madrid, Spain. ; International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland. ; Scientific Support Office, European Space Research and Technology Centre/ESA, Keplerlaan 1, Postbus 299, 2201 AZ Noordwijk ZH, The Netherlands. ; Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden. ; PAS Space Research Center, Bartycka 18A, 00716 Warszawa, Poland. ; Institut fur Geophysik und extraterrestrische Physik (IGEP), Technische Universitat Braunschweig, Mendelssohnstrasse 3, 38106 Braunschweig, Germany. ; University of Maryland, Department of Astronomy, College Park, Maryland 20742-2421, USA. ; Akademie der Wissenschaften zu Gottingen and Max-Planck-Institut fur Sonnensystemforschung, Justus-von-Liebig Weg 3, 37077 Gottingen, Germany. ; LESIA-Observatoire de Paris, CNRS, Universite Pierre et Marie Curie, Universite Paris Diderot, 5 place J. Janssen, 92195 Meudon, France. ; LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d'Alembert, 78280 Guyancourt, France. ; Department of Industrial Engineering, University of Padova, via Venezia 1, 35131 Padova, Italy. ; University of Trento, Via Mesiano 77, 38100 Trento, Italy. ; INAF-Osservatorio Astronomico, Via Tiepolo 11, 34014 Trieste, Italy. ; Planetary Science Institute, Tucson, Arizona 85719, USA. ; Instituto de Astrofisica de Andalucia (CSIC), Glorieta de la Astronomia s/n, 18008 Granada, Spain. ; National Central University, Graduate Institute of Astronomy, 300 Chung-Da Road, Chung-Li 32054 Taiwan. ; Operations Department, European Space Astronomy Centre/ESA, PO Box 78, 28691 Villanueva de la Canada, Madrid, Spain. ; Institut fur Datentechnik und Kommunikationsnetze der TU Braunschweig, Hans-Sommer Strasse 66, 38106 Braunschweig, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26416730" target="_blank"〉PubMed〈/a〉

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. reddy@mps.mpg.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22582258" target="_blank"〉PubMed〈/a〉

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〉

Description: Images of the martian surface returned by the Imager for Mars Pathfinder (IMP) show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial, aeolian, and impact processes. Analysis of the spectral signatures in the scene (at 440- to 1000-nanometer wavelength) reveal three types of rock and four classes of soil. Upward-looking IMP images of the predawn sky show thin, bluish clouds that probably represent water ice forming on local atmospheric haze (opacity approximately 0.5). Haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, P H -- Bell, J F 3rd -- Bridges, N T -- Britt, D T -- Gaddis, L -- Greeley, R -- Keller, H U -- Herkenhoff, K E -- Jaumann, R -- Johnson, J R -- Kirk, R L -- Lemmon, M -- Maki, J N -- Malin, M C -- Murchie, S L -- Oberst, J -- Parker, T J -- Reid, R J -- Sablotny, R -- Soderblom, L A -- Stoker, C -- Sullivan, R -- Thomas, N -- Tomasko, M G -- Wegryn, E -- New York, N.Y. -- Science. 1997 Dec 5;278(5344):1758-65.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA. psmith@lpl.arizona.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9388170" target="_blank"〉PubMed〈/a〉

Description: Comet Hale-Bopp (C/1995 O1) was observed at wavelengths from 2.4 to 195 micrometers with the Infrared Space Observatory when the comet was about 2.9 astronomical units (AU) from the sun. The main observed volatiles that sublimated from the nucleus ices were water, carbon monoxide, and carbon dioxide in a ratio (by number) of 10:6:2. These species are also the main observed constituents of ices in dense interstellar molecular clouds; this observation strengthens the links between cometary and interstellar material. Several broad emission features observed in the 7- to 45-micrometer region suggest the presence of silicates, particularly magnesium-rich crystalline olivine. These features are similar to those observed in the dust envelopes of Vega-type stars.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Crovisier, J -- Leech, K -- Bockelee-Morvan, D -- Brooke, T Y -- Hanner, M S -- Altieri, B -- Keller, H U -- Lellouch, E -- New York, N.Y. -- Science. 1997 Mar 28;275(5308):1904-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Observatoire de Paris-Meudon, F-92195 Meudon, France.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9072960" target="_blank"〉PubMed〈/a〉

Description: The OSIRIS cameras (optical, spectroscopic, and infrared remote imaging system) onboard the European Space Agency's Rosetta spacecraft observed comet 9P/Tempel 1 for 17 days continuously around the time of NASA's Deep Impact mission. The cyanide-to-water production ratio was slightly enhanced in the impact cloud, compared with that of normal comet activity. Dust particles were flowing outward in the coma at 〉160 meters per second, accelerated by the gas. The slope of the brightness increase showed a dip about 200 seconds after the impact. Dust Afrho values before and long after the impact confirm the slight decrease of cometary activity. The dust-to-water mass ratio was much larger than 1.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Keller, Horst Uwe -- Jorda, Laurent -- Kuppers, Michael -- Gutierrez, Pedro J -- Hviid, Stubbe F -- Knollenberg, Jorg -- Lara, Luisa-Maria -- Sierks, Holger -- Barbieri, Cesare -- Lamy, Philippe -- Rickman, Hans -- Rodrigo, Rafael -- New York, N.Y. -- Science. 2005 Oct 14;310(5746):281-3. Epub 2005 Sep 8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max-Planck Institut fur Sonnensystemforschung, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany. keller@mps.mpg.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16150976" target="_blank"〉PubMed〈/a〉

Description: Neutral oxygen in the saturnian system shows variability, and the total number of oxygen atoms peaks at 4 x 10(34). Saturn's aurora brightens in response to solar-wind forcing, and the auroral spectrum resembles Jupiter's. Phoebe's surface shows variable water-ice content, and the data indicate it originated in the outer solar system. Saturn's rings also show variable water abundance, with the purest ice in the outermost A ring. This radial variation is consistent with initially pure water ice bombarded by meteors, but smaller radial structures may indicate collisional transport and recent renewal events in the past 10(7) to 10(8) years.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Esposito, Larry W -- Colwell, Joshua E -- Larsen, Kristopher -- McClintock, William E -- Stewart, A Ian F -- Hallett, Janet Tew -- Shemansky, Donald E -- Ajello, Joseph M -- Hansen, Candice J -- Hendrix, Amanda R -- West, Robert A -- Keller, H Uwe -- Korth, Axel -- Pryor, Wayne R -- Reulke, Ralf -- Yung, Yuk L -- New York, N.Y. -- Science. 2005 Feb 25;307(5713):1251-5. Epub 2004 Dec 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉University of Colorado, Laboratory for Atmospheric and Space Physics, 234 Innovation Drive, Boulder, CO 80303-7814, USA. larry.esposito@lasp.colorado.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15604361" target="_blank"〉PubMed〈/a〉

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〉