The trapping of mixtures of CO, CH4, N2 and Ar in amorphous water ice was studied experimentally. It is shown that the ice particles could not have been formed at a higher temperature and, subsequently, cool down. Experiments where ice was deposited at elevated temperatures, then cooled down and gas was flowed into the ice, showed that the amount of trapped gas depends only on the highest temperature at which the ice was formed, or resided, prior to cooling and gas flow into it. Consequently,...
Topics: NASA Technical Reports Server (NTRS), AMORPHOUS MATERIALS, COMETS, CRYOTRAPPING, FLYBY MISSIONS,...
An active comet like comet Halley loses by sublimation a surface layer of the order of 1 m thickness per perihelion passage. In situ measurements show that water ice is the main constituent which contributes to the gas emission although even more volatile species (CO, NH3, CH4, CO2 etc.) have been identified. Dust particles which were embedded in the ices are carried by the sublimating gases. Measurements of the chemical composition of cometary grains indicate that they are composed of...
Topics: NASA Technical Reports Server (NTRS), CHEMICAL COMPOSITION, COMETS, ICE, SIMULATION, SUBLIMATION,...
The current views on the origin of life on Earth are discussed briefly, with special emphasis on the chemical evolution of the Earth's primitive atmosphere which was the opening step towards the origin of life. The various forms of shock-waves in the atmosphere: Thunder, meteorite shocks and explosive volcanic eruptions are shown to have been of major importance in the atmospheric evolution, because of their very high efficiency in changing the atmospheric composition and in the formation of...
Topics: DTIC Archive, Bar-Nun, Akiva, TORONTO UNIV DOWNSVIEW (ONTARIO) INST FOR AEROSPACE STUDIES,...
