METEOROID STREAMS AS PROBES OF THE SUBSURFACE REGIONS OF COMETS

Whipple recognized the importance of the rocket-like volatization forc es on a comet nucleus when he formulated his conglomerate model. For n ear-parabolic comets, a determination of an unbound original orbit whe n only gravitational forces are included is commonly believed to be in direct evidence of large neglected nongravitational forces. A comet ca n be given energy either by a symmetric positive transverse nongravita tional force or an asymmetric radial nongravitational force, enhanced during the postperihelion phases. We present evidence describing those new Oort cloud comets which are most likely to have experienced large nongravitational forces. A correlation between enhanced episodic outg assing and the passage of these comets through well-known meteor strea ms is investigated. These results are interpretable as the catalytic i ncrease in volatility as the impacting meteoroids penetrate any surviv ing mantle and probe the icy subsurface regions. If there exists trapp ed gas, either in subsurface pockets or at a crystalline/amorphous-ice interface, then it is much more likely to erupt and expose adjacent u nderlying fresh volatiles when the meteoroids impact the comet, dimini shing the tensile strength of the subsurface crystalline layer. (C) 19 94 Academic Press. Inc.