GAS-RELEASE FROM ICE DUST MIXTURES - RESULTS FROM 11 KOSI EXPERIMENTS/

Porous mixtures of ice from water and other volatile components and df mineral grains were irradiated by artificial sunlight in a space simu lator allowing sample sizes of tens of centimeters. The flow of gases released was measured by means of pressure gauges and a mass spectrome ter, and gas flux densities at the insolated surface were inferred 11 KOSI experiments. Gas release rate is closely related to the developme nt of an outer dust layer depleted of ice At varied composition and ra diative power the decline of sublimation rate during insolation was fo und to be similar for all experiments when the dust/ice ratio was at l east 0.09 by weight. At a lower dust content of 0.02 no dust mantle wa s formed allowing sublimation at a nearly constant rate. Phenomena obs erved by video, IR and ejected particle sensing techniques lead us to conclude that gas flux may be quite inhomogeneously distributed over t he surface where areas covered with and uncovered from dust fluctuate on a scale of centimeters or less. Gas flux rate and its response to r adiative power is shown to be indicative of the evolutionary status of the near-surface part of a porous ice/dust body. Estimates of the coh esive force between grains and of heat conductivity are derived from o ur results. The composition of the released gas is different from that of the ice which has implications for the interpretation of cometary observations.