Impact Excavation on Asteroid 4 Vesta: Hubble Space Telescope Results
Abstract
Hubble Space Telescope images of asteroid 4 Vesta obtained during the favorable 1996 apparition show an impact crater 460 kilometers in diameter near the south pole. Color measurements within the 13-kilometer-deep crater are consistent with excavation deep into a high-calcium pyroxene-rich crust or olivine upper mantle. About 1 percent of Vesta was excavated by the crater formation event, a volume sufficient to account for the family of small Vesta-like asteroids that extends to dynamical source regions for meteorites. This crater may be the site of origin for the howardite, eucrite, and diogenite classes of basaltic achondrite meteorites.
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Vesta is the third largest asteroid with a mean diameter of 530 km (P. C. Thomas et al., Icarus, in press). All other known basaltic asteroids are <10 km in diameter.
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The largest fragment is estimated to be 10 km across. Whether it has the structure of a single coherent fragment or a gravitationally bound group of fragments is unknown, although a conglomerate composition for Vesta fragments is suggested by coincident exposure age peaks for the categories of HED meteorites, as found by O. Eugster and T. Michel [Geochim. Cosmochim. Acta 59, 177 (1995)].
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Based on observations made by the NASA/European Space Agency Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy Inc., under NASA contract NAS 5-26555. Supported in part by STScI grant GO-6481. Helpful suggestions were made by M. Zuber and H. J. Melosh.
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Science
Volume 277 | Issue 5331
5 September 1997
5 September 1997
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Received: 26 June 1997
Accepted: 6 August 1997
Published in print: 5 September 1997
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