Liquid water and organics in Comets:implications for exobiology

摘要

Liquid water in comets, once considered impossible, now appears to be almost certain.New evidence has come from the discovery of clay minerals in comet Tempel 1, which compliments theindirect evidence in aqueous alteration of carbonaceous chondrites. Infrared spectral indication of clayis confirmed by modelling data.in the 8-40 um and 8-12 um wavebands on the basis of mixtures of claysand organics. Radiogenic heating producing liquid water cores in freshly formed comets appears morelikely on current evidence for solar system formation. A second possibility investigated here is transientmelting in comets in the inner solar system, where thin crusts of asphalt-like material, formed due tosolar processing and becoming hot in the daytime, can cause melting of sub-surface icy material a fewcentimetres deep. Supposing comets were seeded with microbes at the time of their formation frompre-solar material, there would be plenty of time for exponential amplification and evolution withinthe liquid interior and in the transient ponds or lakes formed as the outer layers are stripped away viasublimation.