Cometary Chemistry and the Origin of Icy Solar System Bodies, the view after Rosetta

Abstract

In situ research on cometary chemistry began when measurements from the Giotto mission at comet 1P/Halley revealed the presence of complex organics in the coma. New telescopes and space missions have provided detailed remote and in situ measurements of the composition of cometary volatiles. Recently, the Rosetta mission to comet 67P/Churyumov-Gerasimenko more than doubled the number of parent species and the number of isotopic ratios known in comets. 39 of the 66 parent species have also been detected in pre- and proto-stellar clouds, making the similarities of cometary ices with pre-stellar material very intriguing. Most isotopic ratios are non-solar. The variations in D/H in water between different comets indicate a large range in the protoplanetary disk where comets formed. All of these results point to a non-homogeneized protoplanetary disk where comets received their material. This diverse origin is in contrast to the Sun, who received its material from the bulk of the collapsing cloud. Detection of N2 and Ar in the coma of 67P and the presence of very volatile S2 point to low formation temperature of 20-30 K of the comet. The xenon isotopic ratios measured in 67P can explain the long standing question about the origin of the terrestrial atmospheric xenon. While we can exclude comets as being the source of the bulk terrestrial water due to their generally high D/H, the noble gases in the Earth atmosphere are compatible with a cometary delivery. This means that the amount of organics delivered by comets may be highly significant.