Vesta as Seen by IUE: UV Evidence for Space Weathering

摘要

Spectra of asteroid 4 Vesta obtained in October 1990 with the International Ultraviolet Explorer are reinterpreted in light of recent topographic and compositional maps determined from Hubble Space Telescope observations. Vesta displays variations in UV brightness across its surface. The eastern hemisphere (based on the prime meridian defInition of Thomas et ai., 1997b) is darker and somewhat bluer than the western hemisphere. This difference may be due to well-known compositional variations, where the eastern hemisphere is heavier in olivine content. Attempts to model Vesta's spectra in terms of pyroxenes and olivines, however, were largely unsuccessfuL Alternately, the hemispheric difference in UV brightness may be a result of space weathering. The western hemisphere is older and has been exposed to solar wind irradiation longer than the relatively fresh terrain of the eastern hemisphere; the result is a redder UV spectrum.