^1,2Gözen Ertem,³Daniel P.Glavin,⁴Robert P.Volpe,⁵Christopher P.McKay
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114540]
¹SETI Institute, Carl Sagan Center, Mountain View, CA 94043, USA
²Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20742, USA
³NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD, USA
⁴Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
⁵Space Science Division, NASA Ames Research Center, Moffett Field, CA 94035, USA
Copyright Elsevier

Organic compounds have been delivered to the surface of Mars via meteorites, comets and interplanetary dust particles for billions of years. Determining the effects of high energy radiation and galactic cosmic radiation (GCR) on these organic compounds is critical for understanding the potential for the preservation of organic molecules associated with past or present life, and where to look for possible chemical bio- signatures during future Mars missions. Understanding how these effects are attenuated by the mineral matrix and the depth at which they are buried have been challenging to determine in situ on Mars. There have been very few experimental studies on the survival of organic compounds under radiation from a gamma source under realistic conditions, and their interpretation until now has been difficult due to the lack of data for actual radiation levels on Mars. Using the in-situ data obtained by the MSL/RAD instrument to anchor the dose calculations, here we show that the N-heterocycles purine and uracil, crucial components of biochemical processes in extant living systems, mixed with calcite, anhydrite, and kaolinite as Mars analogue minerals can survive the effects of radiation with a dose corresponding to ~500,000 years on Martian surface. The extent of survival varied not only with the nature of the organic compound, but its depth from the surface. These results provide new experimental data for the degree of protection offered by the regolith, in conjunction with minerals, for organic compounds that may be present on Mars.

¹Tak Kunihiro,¹Tsutomu Ota,¹Masahiro Yamanaka,¹Christian Potiszil,¹Eizo Nakamura
Meteoritics & Planatary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13665]
¹The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University, Yamada 827, Misasa, Tottori, 682-0193 Japan
Published by arrangemment with John Wiley & Sons

Sample return missions represent great opportunities to study terrestrially uncontaminated solar system materials. However, the size of returned samples will be limited, and thus, it is necessary to understand the most appropriate techniques to apply. Accordingly, the sensitivity of laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and secondary ion mass spectrometry (SIMS) was compared through the analyses of trace elements in reference materials and the Allende CV3 chondrite. While the SIMS method was found to be more sensitive than the laser method toward all elements of interest, the LA-ICPMS appears to be more suitable in terms of precision for certain elements. Using both analytical techniques, we measured chemical composition of an Allende chondrule and its igneous rim. These data were used to understand the nature of the reservoir that interacted with the host chondrule during formation of its igneous rim. We find that the igneous rim is enriched in silica, alkalis, and rare earth elements compared to the host chondrule. We suggest that the igneous rim could be explained by melting of a mixture of the chondrule-like and REE-enriched CAI-like precursors that accreted on the surface of the host chondrule followed by gas-melt interaction with a silica- and alkali-rich gas. Alternatively, these observations could be interpreted as a result of interaction between the chondrule and the melt resulting from partial melting of a pre-existing planetesimal in the early stages of its differentiation.