Trapping of Gases in Water Ice and Consequences to Comets and the Atmospheres of the Inner Planets

Abstract

This is a brief overview of research on gas trapping in ice, its release from the ice upon warming, and the significance to comets and icy satellites. Whereas gases with low sublimation temperatures-H 2 , D 2 , N e, Ar,Kr,Xe, CO, CH4 and N2 are trapped only in amorphous ice, gases with high sublimation temperatures-CH30H, n-C6H14 and HCN, are trapped also above the transition temperature to crystalline ice. The frac-tionation of Ar, Kr and X e, of CO and N2 and of C2H6 , CH4 and CO during their trapping in the ice at various temperatures, as well as the exponential decrease in the amount of trapped gas as the deposition temperature increases, allows some conclusions regarding the physics of ice and the volatiles inventory in comets and in icy satellites. Evidence is given to the contribution of cometary impacts to the volatile inventory on the inner planets. The ejection of ice grains during massive gas release could hint to the mechanism of crater formation on the surface of comets and to the renewal of their activity at large distances post perihelion, as was observed for comet P fRalley. B. Schmitt et al. (eds.). Solar System lees. 353-366.