¹A. C. Fox,²R. S. Jakubek,³J. L. Eigenbrode
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007624]
¹NASA Postdoctoral Program – NASA Johnson Space Center Houston, TX, USA, Houston
²NASA Johnson Space Center, Jacobs, Houston, TX, 77058 USA
³Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
Published by arranegement with John Wiley & Sons

The search for potential molecular biosignatures on Mars is complicated by its harsh radiation environment that can alter or destroy the primary molecular features diagnostic of an organic compound’s origins. In this work, mixtures of Mars-relevant minerals and organic material representing different types and different chemical

states of sedimentary organic material common in the terrestrial geologic record were irradiated with 200 MeV protons to simulate the effect of exposure to galactic cosmic rays and solar energetic particles over geological timescales and characterized using a deep UV Raman and fluorescence spectrometer analogous to the SHERLOC instrument on the Mars 2020 Perseverance Rover. We found that exposure to ionizing radiation generally results in the loss of molecular features diagnostic of an organic material’s origins in favor of increasingly aromatic compounds or macromolecules. However, these radiolytic effects can be mitigated by the formation of macromolecular structures that are more resistant to radiolysis compared to individual compounds, and potentially through associations with specific minerals that enable increased polymerization. Based on these results, rocks observed by the SHERLOC instrument with fluorescence or Raman features associated with non-aromatic molecular features and/or kerogen-like structures may indicate less radiolytically damaged organic material that should be prioritized for return as it may retain some primary, diagnostic molecular features.

¹C. A. Lorenz,¹M. A. Ivanova,²N. G. Zinovieva,¹K. M. Ryazantsev,¹A. V. Korochantsev
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13951]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Kosygin St. 19, Moscow, 119991 Russia
²Lomonosov Moscow State University, Leninskie Gory, Moscow, 119991 Russia
Published by arrangement with John Wiley & Sons

Metal-rich carbonaceous CB chondrites are generally assumed to be materials accreted from the gas–dust plume formed in catastrophic collisions of planetesimals, at least one of which was differentiated into a metal core and silicate shell. Micron-sized inclusions of siliceous alkali-rich glasses associated with sulfides were found in the metal globules of the Sierra Gorda 013 (SG 013), a CBa-like chondrite. These inclusions are unusual carriers of volatile alkalis which are commonly depleted in CB chondrites. The inclusions are presented by two types: (1) Al-bearing Nb-poor glass associated with daubréelite and (2) Nb-bearing Ca,Al,Mg-poor glass associated with an unknown Na-bearing Cr-sulfide. The glass compositions do not correspond to equilibrium condensation, evaporation, or melting. The Nb-bearing glass has a superchondritic Nb/Ta ratio (31) most likely indicating the fractionation of Nb and Ta in the high-temperature gas–dust impact plume due to condensation from vapor or evaporation of precursor Nb-rich particles. The glasses are interpreted as reaction products between refractory plume condensate particles (or possibly planetary or chondritic solids) with relatively low-temperature K-Na-Si-rich gas in oxidized conditions, possibly in a common plume vapor reservoir. Compositional differences indicate that the glasses and sulfides originated from several different sources under different fO2, fS2, and T conditions and were likely combined together and transported to the metal globule formation region by material flows in the heterogeneous impact plume. The glass–sulfide particles were enclosed in the globules aggregated from smaller solid or molten metal grains. The metal globules were further melted during transport to the high-temperature plume region or by plume shockwave heating. Thus, the composition of the glasses, the host metal, and the main mass of SG 013 shows dynamic heterogeneity of physical conditions and impact plume composition after a large-scale planetesimal collision.