Rosetta target asteroid 2867 Steins: An unusual E‐type asteroid |
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| Authors: | Paul R WEISSMAN Michael D HICKS Paul A ABELL Young‐Jun CHOI Stephen C LOWRY |
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| Institution: | 1. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Mail Stop 183‐301, Pasadena, California, USA;2. Planetary Science Institute, 1700 East Fort Lowell Rd., Suite 106, Tucson, Arizona 85719, USA;3. NASA Johnson Space Center, Mail Code KR, 2101 NASA Parkway, Houston, Texas 77058, USA;4. Korea Astronomy and Planetary Science Institute, 61‐1 Hwaam dong, Yuseong gu, Daejeon 305–348, South Korea;5. Queen's University, Belfast, Astrophysics Research Centre, Department of Physics and Astronomy, Belfast BT7 1NN, UK;6. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Mail Stop 183–301, Pasadena, California 91109, USA |
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| Abstract: | Abstract— ESA's Rosetta spacecraft will fly by main‐belt asteroid 2867 Steins on September 5, 2008. We obtained new visible wavelength spectra of 2867 Steins on December 19, 2006 (UT), using the Palomar 5 m telescope and the facility Double Spectrograph. Two sets of spectra, taken ～3 h apart, one half of the rotation period for 2867 Steins, show it to be an E‐type asteroid. The asteroid displays a 0.50 μm feature that is considered diagnostic of the E(II) sub‐class, but is deeper than any previously observed E‐type. This feature is most likely due to the presence of oldhamite (CaS) on the asteroid's surface. Also, the observed Steins spectra are far redder than any other known E‐types. There is potential evidence for heterogeneity on hemispheric scales, one side of the asteroid appearing to be significantly redder than the other. No known recovered meteorite sample matches the unusual spectra of 2867 Steins, but the closest analog would be similar to an enstatite achondrite (aubrite). |
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