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Vesta's UV Lightcurve: Hemispheric Variation in Brightness and Spectral ReversalSpectra of asteroid 4 Vesta obtained in October 1990 with the International Ultraviolet Explorer are reanalyzed and reinterpreted. A large portion of the eastern hemisphere (based on the prime meridian definition of Thomas et al., 1997a) is darker at UV Wavelengths than much of the western hemisphere. The UV lightcurve is in contrast with the visible lightcurve, which shows that the eastern hemisphere is brighter than the western. These IUE spectra of Vesta thus may be evidence for the "spectral reversal." first seen on the Moon by Apollo 17. where the visibly brighter lunar highlands are darker than the maria at far-UV wavelengths. This effect was linked to space weathering when it was noted (Wagner et al., 1987) that the spectral reversal appears in the laboratory spectra of lunar soils but not powdered lunar rocks. We investigate Vesta's UV lightcurve and spectral reversal, and its possible connection with space weathering. The addition to grain coatings of small amounts of submicroscopic iron (SMFe) through vapor deposition causes drastic spectral changes at UV-visible wavelengths (Hapke, 2001). while the longer wavelength spectrum remains largely unaffected. Other laboratory results (e.g., Hiroi and Pieters, 1998) indicate that the UV-visible wavelength range is affected by simulated weathering processes in a manner similar to what is seen on Vesta. It is likely that Vesta has experienced relatively minor amounts of space weathering, as indicated by the spectral reversal, along with the subtle visible-near infrared weathering effects (e.g., Binzel et al., 1997).
Document ID
20040045270
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
Authors
Hendrix, Amanda R.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Vilas, Faith
(NASA Johnson Space Center Houston, TX, United States)
Festou, Michael
(Observatoire de Midi-Pyrenees Toulouse, France)
Date Acquired
August 21, 2013
Publication Date
January 1, 2003
Publication Information
Publication: Icarus
Publisher: Elsevier Science
Volume: 162
ISSN: 0019-1035
Subject Category
Lunar And Planetary Science And Exploration
Funding Number(s)
CONTRACT_GRANT: NAG9-1209
Distribution Limits
Public
Copyright
Other

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