From the interstellar medium to planetary atmospheres via comets

Laboratory experiments on the trapping of gases by ice forming at low temperatures implicate comets as major carriers of the heavy noble gases to the inner planets. Recent work on deuterium in Comet Hale-Bopp provides good evidence that comets contain some unmodified interstellar material. However, if the sample of three comets analyzed so far is typical, Earth's oceans cannot have been produced by comets alone. The highly fractionated neon in Earth's atmosphere also indicates the importance of non-icy carriers of volatiles, as do the noble gas abundances in meteorites from Mars.