Aqueous Alteration On Asteroids Simplifies Soluble Organic Matter Mixtures


This is one of the Tagish Lake meteorite fragments. Credit: Michael Holly, Creative Services, University of Alberta.

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 SchulzZimm (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 over C ratios of SOM decrease with increasing aqueous alteration, and the estimate of H loss from the SOM is 10% to 30%. Organics seem to be a significant H2 source that may have caused subsequent chemical reactions in the Tagish Lake meteorite parent body.

Junko Isa, François-régis Orthous-Daunay, Pierre Beck, Christopher D. K. Herd, Veronique Vuitton, Laurène Flandinet

Comments: 29 pages
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Data Analysis, Statistics and Probability (physics.data-an)
Journal reference: ApJL 920 L39 (2021)
DOI: 10.3847/2041-8213/ac2b34
Cite as: arXiv:2111.10004 [astro-ph.EP] (or arXiv:2111.10004v1 [astro-ph.EP] for this version)
Submission history
From: Junko Isa
[v1] Fri, 19 Nov 2021 01:42:49 UTC (2,826 KB)
https://arxiv.org/abs/2111.10004
Astrobiology, Astrochemistry

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