VESTOIDS AND THEIR RELATIONSHIP TO ASTEROID 4 VESTA
Vestoids are relatively small objects, usually with estimated diameters of 10 km or less. Approximately seventy Vestoids have been identified in the main belt and approximately fifteen Vestoids in the near-Earth asteroid population on the basis of visible and/or near-infrared reflectance spectra.
We have obtained near-infrared reflectance spectra of a number of Vestoids using the SpeX instrument at the NASA IRTF (Infrared Telescope Facility), which allow for average pyroxene mineralogies to be estimated for these objects since the SpeX spectra encompass both the 1 and 2 ìm absorption features. SpeX spectra have currently been obtained on Vesta and approximately twenty-five main-belt and near-Earth Vestoids. These spectra are currently being analyzed to try to determine the mineralogies of these objects and the minimum ejection velocities from Vesta needed for these objects to reach their present orbits.
Approximately 90% of observed main-belt Vestoids have calculated minimum ejection velocities from Vesta of ~1 km/s or smaller. A few Vestoids have ejection velocities between 1 and 2 km/s. Excluding 1459 Magnya, which is located at 3.15 AU, the only known Vestoid with a minimum ejection velocity from Vesta greater than 2 km/s is 1468 Zomba (2.20 AU). We are currently determining if the composition of the Vestoids varies with minimum ejection velocity from Vesta and if all Vestoids have mineralogies consistent with being derived from Vesta.