Delivery of dark material to Vesta via carbonaceous chondritic impacts

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 E.C. Scully, Elizabeth M. Palmer, Holger Sierks, Paul J. Mann, Kris J. Becker, Andrew W. Beck, David Mittlefehldt, Jian Yang Li, Robert Gaskell, Christopher T. RussellMichael J. Gaffey, Harry Y. McSween, Thomas B. McCord, Jean Philippe Combe, David Blewett

Research output: Contribution to journalArticlepeer-review

144 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)544-559
Number of pages16
JournalIcarus
Volume221
Issue number2
DOIs
StatePublished - Nov 2012
Externally publishedYes

Keywords

  • Asteroid Vesta
  • Asteroids, Composition
  • Mineralogy
  • Spectroscopy

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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