Molecular composition of short-period comets from millimetre-wave spectroscopy: 21P/Giacobini-Zinner, 38P/Stephan-Oterma, 41P/Tuttle-Giacobini-Kresák, and 64P/Swift-Gehrels

Abstract

We present the results of millimetre-wave spectroscopic observations and spectral surveys of the following short-period comets: 21P/Giacobini-Zinner in September 2018, 41P/Tuttle-Giacobini-Kresák in April 2017, and 64P/Swift-Gehrels and 38P/Stephan-Oterma in December 2018, carried out with the Institut de RadioAstronomie Millimétrique (IRAM) 30-m radio telescope at wavelengths between 1 and 3 mm. Comet 21P was also observed in November 1998 with the IRAM 30-m, James Clerk Maxwell Telescope, and the Caltech submillimeter Observatory radio telescopes at wavelengths from 0.8 to 3 mm. The abundances of the following molecules have been determined in those comets: HCN, CH3OH, CS, H2CO, CH3CN, and H2S in comet 21P; HCN and CH3OH in 41P; HCN, CH3OH, and CS in 64P; and CH3OH in 38P. The last three comets, classified as carbon-chain typical from visible spectro-photometry, are relatively rich in methanol (3.5–5% relative to water). On the other hand, comet 21P, classified as carbon-chain depleted, shows abundances relative to water which are low for methanol (1.7%), very low for H2S (0.1%), and also relatively low for H2CO (0.16%) and CO (<2.5%). Observations of comet 21P do not show any change in activity and composition between the 1998 and 2018 perihelions. Sensitive upper limits on the abundances of other molecules such as CO, HNCO, HNC, or SO are also reported for these comets.

Parent Volatile Outgassing Associations in Cometary Nuclei: Synthesizing Rosetta Measurements and Ground-based Observations

“…Ammonium salts (NH 4 + X − ) can form with the interaction of ammonia with molecules such as HCN, HNCO, and HCOOH at the low temperatures presented in the comet formation regions in the protoplanetary disk midplane. The main nitrogen-bearing species in comets, NH 3 , NH 2 , HCN (and its isomer HNC), CH 3 CN, and HC 3 N, have emission features in the near-IR and radio wavelengths (see Biver & Bockelee-Morvan 2015, Dello Russo et al 2016bBockelée-Morvan & Biver 2017;Lippi et al 2021;Biver et al 2022), and the detection or stringent upper limits of these molecules have been reported in many comets to date (e.g., Dello Russo et al 2016b;Biver et al 2018Biver et al , 2021Saki et al 2021;Biver et al 2022;Dello Russo et al 2022;Khan et al 2023). Ammonium salts are hard to detect in general, as they are unstable in the gas phase and their infrared signature is often hidden.…”

“…The Space Telescope Imaging Spectrograph on the Hubble Space Telescope measured the sulfur-bearing species CS in comet 67P during the 2021 apparition (Noonan et al 2023) and discovered significant variations from both Rosetta measurements (Calmonte et al 2016) and radio observations (Coulson et al 2020;Biver et al 2021). Higher levels of CS/H 2 O (derived from CS and OH) were seen compared to in situ measurements, challenging the previous assumption that CS is a direct product of CS 2 dissociation, as it was also shown in radio millimeter and submillimeter observations of comets.…”

Gas chromatography coupled-to Fourier transform orbitrap mass spectrometer for enantioselective amino acid analyses: Application to pre-cometary organic analog

“…These interplanetary bodies are indeed considered to have evolved little since the formation of the solar system and thus possess a primitive organic content [1][2][3] . To characterize this organic matter, ground-based or space observations are possible, but are limited to the identification of molecules either in the gas phase [4][5][6] or to the surface characterization mainly by infrared spectroscopy [7][8][9] . However, space missions have been designed to visit interplanetary bodies in order to obtain a more precise characterization of their organic content 10 .…”