Cometary Chemistry and the Origin of Icy Solar System Bodies: The View After Rosetta

In situ research of 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 (67P) more than doubled the number of parent species and the number of isotopic ratios known for comets. Forty of the 71 parent species have also been detected in pre- and protostellar clouds. Most isotopic ratios are nonsolar. This diverse origin is in contrast to that of the Sun, which received its material from the bulk of the collapsing cloud. The xenon isotopic ratios measured in 67P can explain the long-standing question about the origin of terrestrial atmospheric xenon. These findings strengthen the notion that comets are indeed an important link between the ISM and today's solar system including life on Earth. Nonsolar isotopic ratios for species such as Xe, N, S, and Si point to a nonhomogenized protoplanetary disk from which comets received their material. The similarity of the organic inventories of comets and presolar and protostellar material makes it plausible that this material was accreted almost unaltered by comets from the presolar stage. Large variations in the deuterium-to- hydrogen ratio in water for comets indicate a large range in the protoplanetary disk from which comets formed. The amount of organics delivered by comets to Earth may be highly significant.