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Delivery of dark material to Vesta via carbonaceous chondritic impacts |
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| Authors: | Vishnu Reddy Lucille Le Corre David P O’Brien Andreas Nathues Edward A Cloutis Daniel D Durda William F Bottke Megha U Bhatt David Nesvorny Debra Buczkowski Jennifer EC Scully Elizabeth M Palmer Holger Sierks Paul J Mann Kris J Becker Andrew W Beck David Mittlefehldt Jian-Yang Li David Blewett |
| Institution: | 1. Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany;2. Department of Space Studies, University of North Dakota, Grand Forks, USA;3. Planetary Science Institute, Tucson, AZ, USA;4. Department of Geography, University of Winnipeg, Manitoba, Canada;5. Southwest Research Institute, Boulder, CO, USA;6. Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA;7. Institute of Geophysics and Planetary Physics, University of California Los Angeles, Los Angeles, CA, USA;8. Astrogeology Science Center, U.S. Geological Survey, Flagstaff, AZ, USA;9. Department of Mineral Sciences, Smithsonian National Museum of Natural History, 10th and Constitution NW, Washington, DC, USA;10. Astromaterials Research Office, NASA Johnson Space Center, Mail Code KR, Houston, TX, USA;11. Department of Astronomy, University of Maryland, College Park, MD, USA;12. Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN, USA;13. Bear Fight Institute, Winthrop, WA, USA |
| Abstract: | NASA’s Dawn spacecraft observations of Asteroid (4) Vesta reveal a surface with the highest albedo and color variation of any asteroid we have observed so far. Terrains rich in low albedo dark material (DM) have been identified using Dawn Framing Camera (FC) 0.75 μm filter images in several geologic settings: associated with impact craters (in the ejecta blanket material and/or on the crater walls and rims); as flow-like deposits or rays commonly associated with topographic highs; and as dark spots (likely secondary impacts) nearby impact craters. This DM could be a relic of ancient volcanic activity or exogenic in origin. We report that the majority of the spectra of DM are similar to carbonaceous chondrite meteorites mixed with materials indigenous to Vesta. Using high-resolution seven color images we compared DM color properties (albedo, band depth) with laboratory measurements of possible analog materials. Band depth and albedo of DM are identical to those of carbonaceous chondrite xenolith-rich howardite Mt. Pratt (PRA) 04401. Laboratory mixtures of Murchison CM2 carbonaceous chondrite and basaltic eucrite Millbillillie also show band depth and albedo affinity to DM. Modeling of carbonaceous chondrite abundance in DM (1–6 vol.%) is consistent with howardite meteorites. We find no evidence for large-scale volcanism (exposed dikes/pyroclastic falls) as the source of DM. Our modeling efforts using impact crater scaling laws and numerical models of ejecta reaccretion suggest the delivery and emplacement of this DM on Vesta during the formation of the ～400 km Veneneia basin by a low-velocity (<2 km/s) carbonaceous impactor. This discovery is important because it strengthens the long-held idea that primitive bodies are the source of carbon and probably volatiles in the early Solar System. |
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