Oxygen-bearing organic molecules in comet 67P’s dusty coma: First evidence for abundant heterocycles

¹ Physics Institute, Space Research & Planetary Sciences, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
e-mail: nora.haenni@unibe.ch
² Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS, 91405 Orsay, France
³ Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA
⁴ Space Science Division, Southwest Research Institute, San Antonio, TX, USA
⁵ Department of Physics and Astronomy, The University of Texas at San Antonio, San Antonio, TX, USA
⁶ Royal Belgian Institute for Space Aeronomy, BIRA-IASB, Brussels, Belgium
⁷ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland

Received: 31 May 2023
Accepted: 26 July 2023

Abstract

The puzzling complexity of terrestrial biomolecules is driving the search for complex organic molecules in the interstellar medium (ISM) and serves as a motivation for many in situ studies of reservoirs of extraterrestrial organics, from meteorites and interplanetary dust particles to comets and asteroids. Comet 67P/Churyumov-Gerasimenko (67P), the best-studied comet to date, has been visited and accompanied for 2 yr by the European Space Agency’s Rosetta spacecraft. Around 67P’s perihelion and under dusty conditions, the high-resolution mass spectrometer on board Rosetta has provided a spectacular glimpse into this comet’s chemical complexity. For this work, we analyzed the O-bearing organic volatiles in unprecedented detail. Through a comparison of 67P’s inventory with molecules detected in the ISM, in other comets, and in soluble organic matter extracted from the Murchison meteorite, we also highlight the (pre)biotic relevance of different chemical groups of species. We report first evidence for abundant extraterrestrial O-bearing heterocycles (with abundances relative to methanol often on the order of 10% and a relative error margin of 30–50%) and various representatives of other molecule classes, such as carboxylic acids and esters, aldehydes, ketones, and alcohols. As with the pure hydrocarbons, some hydrogenated forms seem to be dominant over their dehydrogenated counterparts. An interesting example is tetrahydrofuran, as it might be a more promising candidate for searches in the ISM than the long-sought furan. Our findings not only support and guide future efforts to investigate the origins of chemical complexity in space, but they also strongly encourage the study, in the laboratory as well as by modeling, of such topics as the ratios of unbranched versus branched species and hydrogenated versus dehydrogenated species in astrophysical ice analogs.