AQUEOUS ALTERATION ON ASTEROIDS SIMPLIFIES SOLUBLE ORGANIC MATTER MIXTURES

• Main Authors: Isa, Junko, Orthous-Daunay, François-Régis, Beck, Pierre, Herd, Christopher, Vuitton, Véronique, Flandinet, Laurène
• Other Authors: Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales Toulouse (CNES)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP]; Tagish; Tagish Lake
• Online Access: https://hal-cnrs.archives-ouvertes.fr/hal-03414598; https://hal-cnrs.archives-ouvertes.fr/hal-03414598/document; https://hal-cnrs.archives-ouvertes.fr/hal-03414598/file/TL_SOM_manuscript_ForApJL_revision_rerevision.pdf

International audience Biologically relevant abiotic extraterrestrial soluble organic matter (SOM) has been widely investigated to study the origin of life and the chemical evolution of protoplanetary disks. Synthesis of biologically relevant organics, in particular, seems to require aqueous environments in the early solar system. However, SOM in primitive meteorites includes numerous chemical species besides the biologically relevant ones and the reaction mechanisms that comprehensively explain the complex nature of SOM are unknown. Besides, the initial reactants, which formed before asteroid accretion, were uncharacterized. We examined the mass-distribution of SOM extracted from three distinct Tagish Lake meteorite fragments, which exhibit different degrees of aqueous alteration though they originated from a single asteroid. We report that mass-distributions of SOM in the primordial fragments are well fit by the Schulz-Zimm (SZ) model for the molecular weight distribution patterns found in chain-growth polymerization experiments. Also, the distribution patterns diverge further from SZ with increasing degrees of aqueous alteration. These observations imply that the complex nature of the primordial SOM 1) was established before severe alteration on the asteroid, 2) possibly existed before parent body accretion, and 3) later became simplified on the asteroid. Therefore, aqueous reactions on asteroids are not required conditions for cultivating complex SOM. Furthermore, we found that overall H/C ratios of SOM decrease with increasing of aqueous alteration, and the estimate of H loss from the SOM is 10-30%. Organics seem to be a significant H2 source that may have caused subsequent chemical reactions in the Tagish Lake meteorite parent body.