Abstract
Primitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects.
Highlights
Comets are the least processed objects in the solar system
Only in 1986 did the European Space Agency’s (ESA) Giotto mission and the Soviet Vega 2 mission flying by comet 1P/Halley (Reinhard 1986) confirm that comets possess a solid nucleus composed of volatile and refractory materials
Starting from the variation of the 14N/15N ratios observed in the interstellar medium to the more or less uniform value in the molecules observed in comets, to the Sun and the planets makes this an important object to study the provenance of the material in the solar system
Summary
Comets are the least processed objects in the solar system. Studying them allows us to gather precious information about the early days of our solar system and possibly even beyond. Only in 1986 did the European Space Agency’s (ESA) Giotto mission and the Soviet Vega 2 mission flying by comet 1P/Halley (Reinhard 1986) confirm that comets possess a solid nucleus composed of volatile and refractory materials. Numerous spectroscopic and photometric observation campaigns of cometary comae have been performed from Earth- and space-based telescopes (see e.g. Biver et al 2002; BockeléeMorvan et al 2004; Mumma et al 1996, 2003, 2005; Dello Russo et al 2007, and Lis et al 2019) These observations have greatly increased the sample of investigated comets and led to many discoveries and allowed for a detailed comparison between comets, other solar system objects, and all the way to the interstellar medium. We refer to the paper by Weissman et al (2020) on the formation and dynamical history of cometary nuclei
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