Identification and characterization of a new ensemble of cometary organic molecules

Abstract

In-situ study of comet 1P/Halley during its 1986 apparition revealed a surprising abundance of organic coma species. It remained unclear, whether or not these species originated from polymeric matter. Now, high-resolution mass-spectrometric data collected at comet 67P/Churyumov-Gerasimenko by ESA’s Rosetta mission unveil the chemical structure of complex cometary organics. Here, we identify an ensemble of individual molecules with masses up to 140 Da while demonstrating inconsistency of the data with relevant amounts of polymeric matter. The ensemble has an average composition of C1H1.56O0.134N0.046S0.017, identical to meteoritic soluble organic matter, and includes a plethora of chain-based, cyclic, and aromatic hydrocarbons at an approximate ratio of 6:3:1. Its compositional and structural properties, except for the H/C ratio, resemble those of other Solar System reservoirs of organics—from organic material in the Saturnian ring rain to meteoritic soluble and insoluble organic matter –, which is compatible with a shared prestellar history.

The Evolution of Activity and Chemical Composition in Rosetta’s Comet Targets across Multiple Apparitions: Complications for CS2 as the CS Parent in Comet Nuclei

“…Further, their photodissociation rates may be large enough that they would appear as a nuclear CS 2 source, but more laboratory work investigating the production and destruction of these polymers in astrophysical conditions is needed. ROSINA identified very few molecules with masses over 50 amu, and only a few of those were sulfur bearing (Hänni et al 2022), so the polymerization of CS 2 may be unlikely. Identifying correlation between comet dynamical type and preferred CS parent length scale and comparing to protoplanetary disk chemical models that take into account sulfur UV photochemistry would be one way to examine this hypothesis theoretically.…”

Multi-instrument analysis of 67P/Churyumov-Gerasimenko coma particles: COPS-GIADA data fusion

“…COPS is one of the three sensors of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA, Balsiger et al 2007). The other two are mass spectrometers: the Reflectron Time-of-Flight mass spectrometer (RTOF) and the Double Focusing Mass Spectrometer (DFMS), which have been employed to determine the elemental, molecular, and isotopic composition and abundances in 67P (e.g., Rubin et al 2019;Altwegg et al 2020;Müller et al 2022;Hänni et al 2022).…”

“…These particles are much larger than those detected by COPS. Nevertheless, COPS would also measure species of lower volatility compared to water, such as the numerous salts and organics found by DFMS (e.g., Altwegg et al 2020Altwegg et al , 2022Hänni et al 2022). The volatility of many of these identified species is low enough to survive, at least in parts, the travel between 67P's surface and the spacecraft even if the situation is complicated due to varying cometocentric distance of the Rosetta spacecraft coupled with heliocentric distance and dust sizes, velocities, composition, structure, and shapes.…”

Gas Sources from the Coma and Nucleus of Comet 46P/Wirtanen Observed Using ALMA

“…Conversely, Milam et al (2006) noted a lack of evidence for POM in Giotto mass spectra of comet Halley and argued that it constitutes an unlikely source of H 2 CO in the coma. Furthermore, mass spectrometry by the Rosetta mission found no evidence for POM in comet 67P (Hänni et al 2022), so alternative explanations may be required to explain the distributed H 2 CO source. Moreover, given the limited sample size and large disparity between the observed L p (H 2 CO) values, it will be important to conduct more observations of H 2 CO distributions in different comets over a range of coma size scales at differing heliocentric distances to better characterize the behavior of the H 2 CO source(s) and help constrain the properties of its still-elusive parent.…”