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The Galileo Encounters with Gaspra and IDA

Published online by Cambridge University Press:  19 July 2016

Clark R. Chapman
Clark R. Chapman*
Affiliation:
Planetary Science Institute, 620 N. 6th Avenue, Tucson, Arizona 85705 E-mail cchapman@nasamail.nasa.gov

Abstract

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The Galileo spacecraft encounters with 951 Gaspra and 243 Ida have provided the first close-up pictures and measurements of asteroids. These two small, S-type asteroids are both irregular in shape, confirming generalized pre-encounter interpretations from groundbased data. Gaspra is lightly cratered by small, fresh craters whereas Ida's surface is heavily covered by craters of all sizes and in all stages of degradation. Unless there are major differences in strength between these two bodies, Ida may be about 10 times older than Gaspra – approaching the age of the solar system. Both asteroids have grooves, although not as prominent as on Phobos. Ida has a population of boulders, particularly near its ends. While Ida seems to have a deep regolith, Gaspra is more nearly in a state of erosion, although there is evidence for an older megaregolith. The data are thus far not conclusive about the geophysical properties of these objects (e.g. whether they are rubble piles) and there are as yet no firm conclusions about how asteroid families are produced by catastrophic collisions. Interesting spectral data relevant to the S-type asteroid controversy (e.g. spatial variations on Gaspra) may lead to some useful generalizations after the remaining Ida data are returned and analyzed in spring 1994. Unexpected magnetic anomalies observed in the vicinities of both asteroids are being studied.

Type
Observations for Space
Information
Symposium - International Astronomical Union , Volume 160: Asteroids, Comets, Meteors 1993 , 1994 , pp. 357 - 365
Copyright
Copyright © Kluwer 1994 

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