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A New Dawn

Since 17 July 2011, NASA's spacecraft Dawn has been orbiting the asteroid Vesta—the second most massive and the third largest asteroid in the solar system (see the cover). Russell et al. (p. 684) use Dawn's observations to confirm that Vesta is a small differentiated planetary body with an inner core, and represents a surviving proto-planet from the earliest epoch of solar system formation; Vesta is also confirmed as the source of the howardite-eucrite-diogenite (HED) meteorites. Jaumann et al. (p. 687) report on the asteroid's overall geometry and topography, based on global surface mapping. Vesta's surface is dominated by numerous impact craters and large troughs around the equatorial region. Marchi et al. (p. 690) report on Vesta's complex cratering history and constrain the age of some of its major regions based on crater counts. Schenk et al. (p. 694) describe two giant impact basins located at the asteroid's south pole. Both basins are young and excavated enough amounts of material to form the Vestoids—a group of asteroids with a composition similar to that of Vesta—and HED meteorites. De Sanctis et al. (p. 697) present the mineralogical characterization of Vesta, based on data obtained by Dawn's visual and infrared spectrometer, revealing that this asteroid underwent a complex magmatic evolution that led to a differentiated crust and mantle. The global color variations detailed by Reddy et al. (p. 700) are unlike those of any other asteroid observed so far and are also indicative of a preserved, differentiated proto-planet.

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.

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References and Notes

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Published In

Science
Volume 336 | Issue 6082
11 May 2012

Submission history

Received: 13 January 2012
Accepted: 13 April 2012
Published in print: 11 May 2012

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Acknowledgments

We thank the Dawn team for the development, cruise, orbital insertion, and operations of the Dawn spacecraft at Vesta. The Framing Camera project is financially supported by the Max Planck Society and the German Space Agency, DLR. We also thank the Dawn at Vesta Participating Scientist Program for funding the research. A portion of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Dawn data are archived with the NASA Planetary Data System.

Authors

Affiliations

Vishnu Reddy* [email protected]
Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany.
Department of Space Studies, University of North Dakota, Grand Forks, ND 58202, USA.
Andreas Nathues
Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany.
Lucille Le Corre
Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany.
Holger Sierks
Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany.
Jian-Yang Li
Department of Astronomy, University of Maryland, College Park, MD 20742, USA.
Robert Gaskell
Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA.
Timothy McCoy
Department of Mineral Sciences, Smithsonian National Museum of Natural History, 10th and Constitution NW, Washington, DC 20560–0119, USA.
Andrew W. Beck
Department of Mineral Sciences, Smithsonian National Museum of Natural History, 10th and Constitution NW, Washington, DC 20560–0119, USA.
Stefan E. Schröder
Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany.
Carle M. Pieters
Department of Geological Sciences, Brown University, Providence, RI 02912, USA.
Kris J. Becker
Astrogeology Science Center, U.S. Geological Survey, Flagstaff, AZ 86001, USA.
Bonnie J. Buratti
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
Brett Denevi
Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
David T. Blewett
Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
Ulrich Christensen
Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany.
Michael J. Gaffey
Department of Space Studies, University of North Dakota, Grand Forks, ND 58202, USA.
Pablo Gutierrez-Marques
Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany.
Michael Hicks
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
Horst Uwe Keller
Institut für Geophysik und extraterrestrische Physik, TU Braunschweig Mendelssohnstrasse 3, DE 38106 Braunschweig, Germany.
Thorsten Maue
Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany.
Stefano Mottola
Deutsches Zentrum für Luft und Raumfahrt (DLR)–German Aerospace Center, Institute of Planetary Research, Rutherfordstrasse 2, D-12489 Berlin, Germany.
Lucy A. McFadden
NASA/Goddard Space Flight Center, Mail Code 160, Greenbelt, MD 20771, USA.
Harry Y. McSween
Department of Earth and Planetary Sciences, University of Tennessee, 1412 Circle Drive, Knoxville, TN 37996–1410, USA.
David Mittlefehldt
Astromaterials Research Office, NASA Johnson Space Center, Mail Code KR, Houston, TX 77058, USA.
David P. O’Brien
Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA.
Carol Raymond
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
Christopher Russell
Institute of Geophysics and Planetary Physics, University of California Los Angeles, Los Angeles, CA 90024–1567, USA.

Notes

*
To whom correspondence should be sent. E-mail: [email protected]

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