Volatile Species in Comet 67P/Churyumov-Gerasimenko: Investigating the Link from the ISM to the Terrestrial Planets

Abstract

150-250 words)Comets contain abundant amounts of organic and inorganic species. Many of the volatile molecules in comets have also been observed in the interstellar medium and some of them even with similar relative abundances, indicating formation under similar conditions or even sharing a common chemical pathway. There is a growing amount of evidence that suggests comets inherit and preserve substantial fractions of materials inherited from previous evolutionary phases, potentially indicating that commonplace processes occurred throughout comet-forming regions. Through impacts, part of this material has also been transported to the inner planetary system, including the terrestrial planets. While comets have been ruled out as a major contributor to terrestrial ocean water, substantial delivery of volatile species to the Earth's atmosphere, and as a consequence also organic molecules to its biomass, appears more likely. Comets contain many species of pre-biotic relevance and molecules that are related to biological processes on Earth, and have hence been proposed as potential indicators for the presence of biological processes in the search of extraterrestrial life. While the delivery of cometary material to Earth may have played a crucial role in the emergence of life, the presence of such alleged biosignature molecules in the abiotical environment of comets complicates the detection of life elsewhere in the universe.

On the Origin and Evolution of the Material in 67P/Churyumov-Gerasimenko

“…A contribution of 22 ± 5% to the terrestrial atmosphere was derived based on the xenon isotopic composition of 67P/C-G compared to the terrestrial atmosphere (Marty et al 2017). As a consequence, also copious amounts of organic species would have found their way to the inner solar system and the Earth (Marty et al 2016;Rubin et al 2019b).…”

Extraterrestrial hexamethylenetetramine in meteorites—a precursor of prebiotic chemistry in the inner solar system

“…Although the composition of products varies depending on the experimental conditions, HMT is generally abundant especially when methanol is used as an initial reactant 16,18,20 . Since methanol is abundant in interstellar ices 3 , the HMT formation is likely to take place in the interstellar medium (ISM) and become incorporated into solar system ices similar to other interstellar molecules 21,22 .…”

Organic Matter in Cometary Environments

“…The organic content of comets suggests they could be an important source of the Earth’s current biosphere. Using the measurements of organic matter in comet 67P by Rosetta, Rubin et al 2019 [ 137 ] and Altwegg et al 2019 [ 65 ] argued that comets could account for all of the organic material currently present in Earth’s biosphere.…”

“…For comets with a range of values from different works, we used the average of these values when calculating mean values for the population. In addition to the species below, Rosetta quantified the following species that have been detected remotely in other comets: HNCO/H O = 0.027%, CH CN/H O = 0.006%, HC N/H O = 0.0004%, HCOOH/H O = 0.013%, HCOOCH /H O = 0.003%, CH CHO/H O = 0.047%, (CH OH) /H O = 0.011%, C H OH/H O = 0.039%, NH CHO/H O = 0.004%, and H CS/H O = 0.0027% [ 137 , 152 , 153 ].…”