Department of Biology, Georgetown University, Washington, District of Columbia, USA.
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.
Astrobiology. 2024 Nov;24(11):1063-1073. doi: 10.1089/ast.2024.0006. Epub 2024 Oct 22.
Understanding how organics degrade under galactic cosmic rays (GCRs) is critical as we search for traces of ancient life on Mars. Even if the planet harbored life early in its history, its surface rocks have been exposed to ionizing radiation for about four billion years, potentially destroying the vast majority of biosignatures. In this study, we investigated for the first time the impact of simulated GCRs (using gamma rays) on several types of lipid biosignatures (including hopane C, sterane C, alkanes, and fatty acids [FAs]) in both the presence and absence of salts (NaCl, KCl, and MgCl). We measured that the lipids degraded 6-20 times faster than amino acids in similar conditions; moreover, when irradiated in the presence of a salt substrate, degradation was at least 4-6 times faster than without salt, which suggests that salty environments that are often preferred targets for astrobiology warrant caution. We detected radiolytic by-products only for FAs-in the form of alkanes and aldehydes. These results expand our understanding of the degradation of organic molecules in Mars analog environments and underscore the urgent need to direct rover missions to sampling sites protected from GCRs, for example, sites on Mars that have been recently exposed by a wind scarp retreat or meteoritic impact.
了解有机物在银河宇宙射线（GCRs）下的降解方式至关重要，因为我们正在火星上寻找远古生命的痕迹。即使这颗行星在其历史早期存在生命，其表面岩石也已经暴露在电离辐射下约 40 亿年，这可能破坏了绝大多数生物特征。在这项研究中，我们首次研究了模拟 GCR（使用伽马射线）对几种类型的脂质生物标志物（包括藿烷 C、甾烷 C、烷烃和脂肪酸 [FA]）的影响，包括有盐（NaCl、KCl 和 MgCl）和无盐条件下的影响。我们发现，在类似条件下，脂质的降解速度比氨基酸快 6-20 倍；此外，当在盐基质存在下辐照时，降解速度至少比没有盐时快 4-6 倍，这表明经常是天体生物学首选目标的盐环境需要谨慎对待。我们仅在脂肪酸中检测到放射分解产物——以烷烃和醛的形式存在。这些结果扩展了我们对火星模拟环境中有机分子降解的理解，并强调了将漫游车任务直接指向免受 GCR 影响的采样点的迫切需要，例如，火星上最近因风蚀后退或陨石撞击而暴露的地点。
