Variable and Large Losses of Diagnostic Biomarkers After Simulated Cosmic Radiation Exposure in Clay- and Carbonate-Rich Mars Analog Samples.

Mars has been exposed to ionizing radiation for several billion years, and as part of the search for life on the Red Planet, it is crucial to understand the impact of radiation on biosignature preservation. Several NASA and ESA missions are looking for evidence of ancient life in samples collected at depths shallow enough that they have been impacted by galactic cosmic rays (GCRs). In this study, we exposed a diverse set of Mars analog samples to 0.9 Megagray (MGy) of gamma radiation to mimic 15 million years of exposure on the Martian surface. We measured no significant impact of GCRs on the total organic carbon (TOC) and bulk stable C isotopes in samples with initial TOC concentration > 0.1 wt. %; however, diagnostic molecular biosignatures presented a wide range of degradation that didn't correlate to factors like mineralogy, TOC, water content, and surface area. Exposure dating suggests that the surface of Gale crater has been irradiated at more than five times our dose, yet using this relatively low dose and "best-case scenario" geologically recalcitrant biomarkers, large and variable losses were nevertheless evident. Our results empasize the importance of selecting sampling sites at depth or recently exposed at the Martian surface.

Reduction in haze formation rate on prebiotic Earth in the presence of hydrogen.

Recent attempts to resolve the faint young Sun paradox have focused on an early Earth atmosphere with elevated levels of the greenhouse gases methane (CH(4)) and carbon dioxide (CO(2)) that could have provided adequate warming to Earth's surface. On Titan, the photolysis of CH(4) has been shown to create a thick haze layer that cools its surface. Unlike Titan, however, early Earth's atmosphere likely contained high amounts of CO(2) and hydrogen (H(2)). In this work, we examine haze formation in an early Earth atmosphere composed of CO(2), H(2), N(2), and CH(4), with a CO(2)/CH(4) ratio of 10 and a H(2)/CO(2) ratio of up to 15. To initiate aerosol formation, a broad-spectrum ultraviolet (UV) energy source with emission at Lyman-alpha was used to simulate the solar spectrum. Aerosol composition and total aerosol mass produced as a function of reagent gas were measured with an aerosol mass spectrometer (AMS). Results show an order of magnitude decrease in haze production with the addition of H(2), with no significant change in the chemical composition of the haze. We calculate that the presence of H(2) on early Earth could thus have favored warmer surface temperatures and yet allowed photochemical haze formation to deliver complex organic species to early Earth's surface.