Abstract
Comets contain primitive material leftover from the formation of the Solar System, making studies of their composition important for understanding the formation of volatile material in the early Solar System. This includes organic molecules, which, for the purpose of this review, we define as compounds with C–H and/or C–C bonds. In this review, we discuss the history and recent breakthroughs of the study of organic matter in comets, from simple organic molecules and photodissociation fragments to large macromolecular structures. We summarize results both from Earth-based studies as well as spacecraft missions to comets, highlighted by the Rosetta mission, which orbited comet 67P/Churyumov–Gerasimenko for two years, providing unprecedented insights into the nature of comets. We conclude with future prospects for the study of organic matter in comets.
Highlights
The Giotto mission flyby of comet 1P/Halley detected the presence of so-called CHON particles [21]
These CHON particles have been proposed as a possible source for carbon-bearing radicals like C2 observed at optical wavelengths discussed above (e.g., [22,23]), as well as more complex molecules such as formaldehyde (H2 carbon monoxide (CO)) [24]
The development of interferometers, including, but not limited to, the Atacama Large Millimeter/Submillimeter array (ALMA), with sub-arcsecond spatial resolution has revolutionized the study of organic molecules in comets, providing spatially resolved maps of the distributions of species such as hydrogen cyanide (HCN), H2 CO, and CH3 OH (e.g., [48,49,50])
Summary
Comets are rich in simple organic species, such as methanol (CH3 OH), ethane (C2 H6 ), methane (CH4 ), and hydrogen cyanide (HCN) These species have been detected in comets since the 1990s using observations at infrared (IR) and sub-mm wavelengths [5,8]. The Giotto mission flyby of comet 1P/Halley detected the presence of so-called CHON particles (so named because they were rich in carbon, hydrogen, oxygen, and nitrogen) [21] These CHON particles have been proposed as a possible source for carbon-bearing radicals like C2 observed at optical wavelengths discussed above (e.g., [22,23]), as well as more complex molecules such as formaldehyde (H2 CO) [24].
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