What's the Origin of Vesta's Dark Material?

The above image shows a piece of the Murchison meteorite, which fell in Australia. Murchison is one example of carbonaceous chondrite material found on Earth. Image Credit: University of Texas at Arlington

Researchers studying the observations of asteroid 4 Vesta by NASA's Dawn mission, have noticed that the surface has the highest albedo (brightness) and color variation of any asteroid observed to date. Terrains rich in low-albedo dark material have been identified using Dawn's Framing Camera (FC). These terrains include: (1) impact craters (in the ejecta blanket material and/or on the crater walls and rims); (2) flow-like deposits or rays commonly associated with topographic highs; and (3) dark spots (likely secondary impacts) nearby impact craters.

The dark material could be a relic of ancient volcanic activity or exogenic in origin. So think the authors of a new paper that is available for review at arXiv (pronounced "archive"), an online archive of scientific papers, maintained and hosted by Cornell University (arXiv.org). The paper's lead author is Dr. Vishnu Reddy, Research Assistant Professor for the Department of Space Studies at the University of North Dakota.

In the new paper, the research team reports that the majority of the spectra of Vesta's dark material are similar to carbonaceous chondrite meteorites mixed with materials indigenous to Vesta. Using high-resolution seven-color images, the team compared dark material's color properties (albedo, band depth) with laboratory measurements of possible analog materials. They found the band depth and albedo of the dark material to be identical to those of the 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 the Vesta's dark material. In addition, they found the modeling of carbonaceous chondrite abundance in the Vesta dark material is consistent with howardite meteorites. Also, they found no evidence for large-scale volcanism (exposed dikes/pyroclastic falls, etc.) as the source of Vesta's dark material. The team's modeling efforts using impact crater scaling laws and numerical models of ejecta reaccretion have suggested that the delivery and emplacement of Vesta's dark material during the formation of the approximately 400 km Veneneia basin, by a low-velocity (less than 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 (materials easily evaporating at normal temperaturs) in the early Solar System.

To read the paper, visit arxiv.org/abs/1208.2833v1.

The Dawn mission to Vesta and Ceres is managed by NASA’s Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena (Caltech), for NASA’s Science Mission Directorate, Washington D.C. UCLA is responsible for overall Dawn mission science. The Dawn framing cameras have been developed and built under the leadership of the Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany, with significant contributions by DLR German Aerospace Center, Institute of Planetary Research, Berlin, and in coordination with the Institute of Computer and Communication Network Engineering, Braunschweig. The framing camera project is funded by the Max Planck Society, DLR, and NASA/JPL. To learn more about the Dawn mission, visit: www.nasa.gov/dawn and dawn.jpl.nasa.gov .

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