Protective Effects of Halite to Vacuum and Vacuum-Ultraviolet Radiation: A Potential Scenario During a Young Sun Superflare

Halite (NaCl mineral) has exhibited the potential to preserve microorganisms for millions of years on Earth. This mineral was also identified on Mars and in meteorites.

In this study, we investigated the potential of halite crystals to protect microbial life forms on the surface of an airless body (e.g., meteorite), for instance, during a lithopanspermia process (interplanetary travel step) in the early Solar System. To investigate the effect of the radiation of the young Sun on microorganisms, we performed extensive simulation experiments by employing a synchrotron facility.

Optical microscopy images showing the morphology and density of fluid inclusions of a halite crystal (A) and a salt crystal (B), which were obtained in the experiments. (A1, A2) Details of fluid inclusions [of the squared section indicated in (A)]. (B1) Details of fluid inclusions [of the squared section indicated in (B)]. (B2) Section of the wall of another salt crystal of this sample showing multiple tiny fluid inclusions, and the white square shows a measured fluid inclusion as an example. The bright ‘‘X’’ shape observed in halite and salt crystals (A, B, respectively) represents the most rapid directions of growth, along which a few inclusions are trapped. — astro-ph.EP

We focused on two exposure conditions: vacuum (low Earth orbit, 10^{-4}Pa) and vacuum-ultraviolet (VUV) radiation (range 57.6 – 124 nm, flux 7.14 W m^{-2}), with the latter representing an extreme scenario with high VUV fluxes comparable to the amount of radiation of a stellar superflare from the young Sun. The stellar VUV parameters were estimated by using the very well-studied solar analog of the young Sun, k^{1}Cet. To evaluate the protective effects of halite, we entrapped a halophilic archaeon (Haloferax volcanii) and a non-halophilic bacterium (Deinococcus radiodurans) in laboratory-grown halite. Control groups were cells entrapped in salt crystals (mixtures of different salts and NaCl) and non-trapped (naked) cells, respectively.

All groups were exposed either to vacuum alone or to vacuum plus VUV. Our results demonstrate that halite can serve as protection against vacuum and VUV radiation, regardless of the type of microorganism. In addition, we found that the protection is higher than provided by crystals obtained from mixtures of salts. This extends the protective effects of halite documented in previous studies and reinforces the possibility to consider the crystals of this mineral as potential preservation structures in airless bodies or as vehicles for the interplanetary transfer of microorganisms.

Confocal fluorescence microscopy images (1000 · ) of halite crystal-embedded cells of Deinococcus radiodurans co-stained with SYTO 9 and PI, showing characteristics of the crystal, the distribution of microorganisms inside fluid inclusions, and potential damage to the membrane. (A) Color composite (SYTO 9 and PI). (B, C) SYTO 9 and PI signal, respectively. The arrows indicate cells with PI signal without SYTO 9 signal. — astro-ph.EP

Ximena C. Abrevaya, Douglas Galante, Paula M. Tribelli, Oscar J. Oppezzo, Felipe Nobrega, Gabriel G. Araujo, Fabio Rodrigues, Petra Odert, Martin Leitzinger, Martiniano M. Ricardi, Maria Eugenia Varela, Tamires Gallo, Jorge Sanz-Forcada, Ignasi Ribas, Gustavo F. Porto de Mello, Florian Rodler, 1 Maria Fernanda Cerini, Arnold Hanslmeier, Jorge E. Horvath

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2311.08606 [astro-ph.EP] (or arXiv:2311.08606v1 [astro-ph.EP] for this version)
Journal reference: Astrobiology 2023;23(3):245-268
Related DOI:
https://doi.org/10.1089/ast.2022.0016
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Submission history
From: Ximena Celeste Abrevaya
[v1] Wed, 15 Nov 2023 00:04:00 UTC (1,852 KB)
https://arxiv.org/abs/2311.08606
Astrobiology