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J. C. Granahan (BAE SYSTEMS)
On August 28, 1993 the Galileo spacecraft encountered the asteroid 243 Ida and its moon Dactyl. A variety of observations of this asteroid system were collected including visible wavelength (0.4-1.0 microns) imagery with the Solid State Imager (SSI) instrument and infrared wavelength (0.7-5.2 microns) with the Near Infrared Mapping Spectrometer (NIMS). A new analysis of these observations has been conducted using band area analysis, band center measurement, and spectral similarity value measurement using the BAE SYSTEMS Hyperspectral Tool Kit. This abstract reports the initial results of this research effort. These data indicate that 243 Ida has an orthopyroxene/(orthopyroxene + olivine) ratio of about 0.28, a value consistent with that of LL chondrites. The ratio does not vary significantly for the portions of 243 Ida observed by the Galileo NIMS instrument. 243 Ida is a SIV subtype of the S type asteroid population. At least two spectral units were identified in a combined SSI and NIMS spectral data set. The primary difference is the amount of red slope present in the two spectral units. A larger red slope corresponds to regions of 243 Ida where ejecta from the crater Azurra are present. This evidence suggests that impacts enhance the red components of the 243 Ida spectrum, perhaps enhancing the NiFe content.
Dactyl has a relatively deep absorption centered approximately at 0.97 microns with no significant two micron absorption features. This is a possible indicator of clinopyroxene and suggests partial melting or fractional crystallization processes occurred on Dactyl. Dactyl appears to be an SII subtype S type asteroid and is spectrally different from 243 Ida. Dactyl may have been produced by partial melting within the Koronis parent body while the 243 Ida region escaped such igneous processing.
This study was made possible through support from NASA's Planetary Geology and Geophysics program.