David Mittlefehldt

Publications (2)34.59 Total impact

• Source

  Available from: Jian-Yang Li

  Article: 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, [......], Andrew W. Beck, David Mittlefehldt, Jian-Yang Li, Robert Gaskell, Christopher T. Russell, Michael J. Gaffey, Harry Y. McSween, Thomas B. McCord, Jean-Philippe Combe, David Blewett
  [show abstract] [hide abstract]
  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 {\mu}m 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/sec) 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.
  Icarus 11/2012; 221:544-559. · 3.38 Impact Factor
• Source

  Available from: Michael J. Gaffey

  Article: Color and Albedo Heterogeneity of Vesta from Dawn

  Vishnu Reddy, Andreas Nathues, Lucille Le Corre, Holger Sierks, Jian-Yang Li, Robert Gaskell, Timothy McCoy, Andrew W. Beck, Stefan E. Schröder, Carle M. Pieters, [......], Michael Hicks, Horst Uwe Keller, Thorsten Maue, Stefano Mottola, Lucy A. McFadden, Harry Y. McSween, David Mittlefehldt, David P. O’Brien, Carol Raymond, Christopher Russell
  [show abstract] [hide abstract]
  ABSTRACT: Multispectral images (0.44 to 0.98 μm) 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.
  Science 05/2012; 336(6082):700-704. · 31.20 Impact Factor