Rosetta detects macromolecular carbonaceous material in dust particles from Comet Churyumov-Gerasimenko

The COSIMA instrument is under German leadership (MPS Göttingen) with significant French instrumental and scientific contributions. COSIMA is a sort of mini-physicochemical laboratory designed to collect cometary dust particles near the nucleus of Comet Churyumov-Gerasimenko, detect them, and photograph them using the COSISCOPE microscope, developed at the IAS (co-PI-level responsibility), and analyze them using secondary ion mass spectrometry coupled with time-of-flight analysis (ToF-SIMS).

In the study recently published in *Nature*, the team of scientists from the COSIMA experiment—including two co-investigators from the IAS—focused on identifying the carbonaceous material that makes up the dust of Comet Churyumov-Gerasimenko. The authors based their analysis on a comparison of the spectra of cometary grains measured by COSIMA with spectra obtained in the laboratory from reference organic compounds. This led to the conclusion that the detected cometary carbonaceous material has a macromolecular structure.

This result was eagerly awaited by the scientific community. Indeed, this macromolecular carbonaceous material could explain, at least in part, the dark color of the comet’s surface, as observed in particular by the panoramic cameras on the Philae lander (CIVA-P), which is under the responsibility of the IAS. According to analyses conducted by COSIMA, this carbonaceous material detected in the cometary dust is similar to the so-called “insoluble” macromolecular organic matter extracted from certain extraterrestrial materials analyzed in the laboratory (carbonaceous meteorites and micrometeorites, and interplanetary dust). It is also consistent with certain experimental simulations of the evolution of ices under irradiation, conducted notably by the IAS “Astrochemistry and Origins” team, which result in the formation of complex organic matter that is more or less cross-linked—that is, containing macromolecules of varying sizes and quantities, depending on the experimental conditions applied. These observational constraints, combined with simulations and laboratory analyses, will help refine scenarios for the formation and evolution of organic matter in the primordial solar nebula.