DIOGENITE-LIKE FEATURES IN THE SPITZER IRS (5–35μm) SPECTRUM OF 956 ELISA

We report preliminary results from the Spitzer IRS (Infrared Spectrograph) observations of the V-type asteroid 956 Elisa. Elisa was observed as part of a campaign to measure the 5.2–38 micron spectra of small basaltic asteroids with the Spitzer IRS. Targets include members of the dynamical family of the unique large differentiated asteroid 4 Vesta (“Vestoids”), several outer-mainbelt basaltic asteroids whose orbits exclude them from originating on 4 Vesta, and the basaltic near-Earth asteroid 4055 Magellan. 4 Vesta’s dynamical family of small basaltic asteroids is believed to be the proximate source of the HED meteorites, the majority of which are thought to have their ultimate origin on Vesta itself [1, 2] . Hubble imaging of Vesta [3] has revealed an impact basin large enough (D ≈ 460 km) to be the source of all known Vestoids. Spectral studies of Vestoids in the visible and near-IR have characterized their olivine and pyroxene compositions and revealed significant differences between HED and Vestoid populations. For example, about 25% of HED meteorites are diogenites, although to date, observations of diogenite-like near-IR spectra among Vestoids have been very rare; whereas a number of vestoids [e.g. 2579 Spartacus; 4] appear to have olivine-rich compositions not represented among meteorites. Similar NIR features suggest regional olivine exposures on Vesta itself [5, 6].