¹Marceau Lecasble,¹Sylvain Bernard,¹Jean-Christophe Viennet,¹Isis Criouet,¹Laurent Remusat
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115603]
¹Muséum National d’Histoire Naturelle, Sorbonne Université, CNRS UMR 7590, IMPMC, Paris, France
Copyright Elsevier

A variety of polycyclic aromatic hydrocarbons (PAHs) are reported in carbonaceous chondrites (CCs) and in the interstellar medium (ISM). Although PAHs in CCs are not as large as those detected in the ISM, their carbon isotope composition is interpreted as pinpointing an interstellar origin. In contrast, their hydrogen isotope composition can be related to the extent of secondary processes, as is the proportion of alkylated PAHs within CCs. Here, we experimentally investigate the molecular and isotopic evolution of PAHs under simulated asteroidal hydrothermal conditions at 150 °C. Results show that PAHs are chemically stable under these conditions whatever their size, i.e. no destruction, conjugation nor alkylation occurs, even in the presence of other reactive organic molecules. Plus, PAHs retain their carbon isotope compositions even in the presence of another carbon-rich reservoir, either organic or inorganic. On the other hand, their hydrogen isotope composition is modified through exchange with water. Of note, as shown by additional experiments, the presence of smectites, abundant in CCs, impacts the relative abundances of extractable PAHs, saponite trapping more efficiently the larger PAHs. Altogether, results of the present experiments show that PAHs of CCs can be used as tracers of both pre-accretion and secondary processes.

^1,2D.M. Bower et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115626]
¹University of Maryland, Department of Astronomy, College Park, MD 20742, United States of America
²NASA/Goddard Space Flight Center, Greenbelt, MD 20771, United States of America
Copyright Elsevier

Life detection in the solar system relies on the unambiguous identification of signatures of life and habitability. Organic molecules are essential to life as we know it, and yet many organic compounds are ubiquitous in the solar system and can be synthesized abiotically; thus, their presence alone is not indicative of life. On Earth, chemical signatures of life’s processes are often left behind in minerals through the biologically induced formation of secondary minerals or intermediary organic complexes. In natural rocks biomolecules and organic species often co-occur with minerals, and their overlapping peaks can create difficulties in interpretation. In the process of identifying the minerals and organic species in our basaltic samples we noticed signatures for cyanates co-occurring with organic molecules. Cyanates are an overlooked group of nitrogen compounds in which C is bonded to N (e.g., OCN− or SCN−) that often co-occur with urea and ammonium in environments where microorganisms are present. These compounds are common in many terrestrial and oceanic environments and play an important role in biogeochemical nitrogen cycling. In natural systems, these compounds form as the result of multiple biogeochemical pathways, often from the interaction of microbes with a chemically active environment. These interactions leave behind signatures in the form biotic breakdown products such as urea or ammonium and organic reaction byproducts that are observable with spectroscopic methods. To explore these relationships, we used field-portable Raman spectrometers and laboratory micro-Raman imaging to characterize and compare samples collected from two different terrestrial basaltic environments, a lava tube on Mauna Loa, Hawaii, dominated by the precipitation of sulfate minerals and a geothermal stream at Hveragil, Iceland dominated by the precipitation of carbonate minerals. The Raman (RS) measurements were complemented by laser induced breakdown spectroscopy (LIBS), Long-wave Infrared (IR) LIBS, with the addition of gas chromatograph mass spectrometry (GC–MS) and inductively coupled plasma-mass spectrometry (ICP-MS) to identify cyanate compounds, biomolecules, and other nitrogenous compounds related to the breakdown or production of cyanate in host basalts and secondary precipitates. The RS data suggest that the reason for RS cyanate signatures in the carbonate samples could be due to luminescence artifacts while those detected in the host basalts may be due to hydrolysis chemistry. The cyanate signatures detected in the lava tube samples dominated by sulfates do not seem to be luminescence artifacts but may in fact be evidence of an active microbial nitrogen cycle. Our results inform the spectroscopic detection of cyanates in planetary analog environments and the challenges in their identification. Further work is needed to understand their potential as biosignatures on other planetary bodies.

^1,2E. T. DUNHAM,³A. SHEIKH,³D. OPARA,¹N. MATSUDA,^1,4M.-C. LIU,¹K. D. MCKEEGAN
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.13975]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, California 90025,USA
²Department of Earth and Planetary Science, University of California, Santa Cruz, Santa Cruz, California 95064, USA
³Harvard-MIT Science Research Mentoring Program, Boston, Massachusetts 02142, USA
⁴Lawrence Livermore National Laboratory, Livermore, California 94550, USA
Published by arrangement wit John Wiley & Sons

As the Sun was forming, calcium–aluminum-rich inclusions (CAIs) were the firstrocks to have condensed in the hottest regions of the solar nebula disk. Carbonaceouschondrites (CCs) contain abundant CAIs but are thought to have accreted in the outerSolar System, requiring that CAIs must have been transported outward. Curiously, CAIsare rare in ordinary, enstatite, rumuruti, and kakangari chondrites, non-carbonaceouschondrites (NCs), that likely formed in the inner Solar System. Thus, CAI abundances andcharacteristics can provide constraints on the early dynamical evolution of the disk. In thiswork, we address whether the hypothesis of an early-formed proto-Jupiter “opening a gap”in the disk can explain the dichotomy in the relative abundance of CAIs in CC and NCchondrites. We searched 76 NC meteorite sections to find 232 CAIs which have an averageapparent diameter of 46μm and comprise 0.01 area%, about half the size of and~200 timesless abundant than CC CAIs on average. Unlike CC CAIs, only 4% of the NC CAIscontain melilite and most contain alteration features suggesting that NC CAIs underwentpervasive fluid-assisted thermal metamorphism on asteroidal parent bodies. However, basedon NC CAI populations correlating with meteorite metamorphic grade, we argue that diskdynamics is likely the primary reason behind the existence of small (<100μm) and rare NCCAIs. Our data support astrophysical models which suggest that, after outward transport ofCAIs, formation of a gap in the disk trapped CAIs in the outer Solar System.