The recent discovery of organic matter exposed in patches on the surface of the asteroid Ceres has sparked considerable interest in its prospect as an emerging astrobiological target. The dwarf planet’s surface is also characterized by a pervasive display of salt minerals, which are suggestive of briny fluids at depth and ongoing geological activity that resulted in their emplacement. While these salt-rich subsurface liquid reservoirs can present enticing conditions for prebiotic chemistry to emerge, the connection between dissolved organic materials and the associated salt minerals upon exposure to Ceres’ surface environment has not yet been established. Here, we explore this fundamental relationship by investigating the chemistry of putative organic-bearing brines relevant to Ceres (composed of sodium, ammonium, carbonate, and chloride ions) upon freezing using infrared (IR) reflectance and Raman spectroscopies, specifically focusing on two representative amino acids (glycine and aspartic acid) and an N-containing aliphatic compound (hexylamine). The results indicate that the presence of these organic species in the brines leads to the formation of CO₂ (isolated in the water ice matrix) when flash-freezing to liquid nitrogen temperatures. In particular, the two amino acids produce significantly more CO₂ compared to the hexylamine-brine mixture. Slow-freezing conditions, on the other hand, do not exhibit such a behavior. The bicarbonate anions in solution (rather than the amino acids themselves) are confirmed to be the source of CO₂ by isotopic substitution experiments. Raman measurements subsequently hint at a possible reaction pathway involving the formation of a carbamate intermediate. These results not only exemplify the potentially important role of organic-salt interactions in Ceres’ evolution, but also provide insights into the fate of organics and future detection strategies of organic deposits on ocean worlds.

中文翻译：

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氨基酸介导的速冻谷神盐水中二氧化碳的形成

最近在小行星谷神星表面发现的有机物暴露的斑块引起了人们对其作为新兴天体生物学目标的前景的极大兴趣。这颗矮行星表面的另一个特点是普遍存在盐矿物，这表明深部存在咸水流体以及导致其侵位的持续地质活动。虽然这些富含盐的地下液体储层可以为生命前化学的出现提供诱人的条件，但在暴露于谷神星表面环境时溶解的有机物质与相关盐矿物之间的联系尚未建立。在这里，我们通过使用红外（IR）反射率和拉曼光谱研究与谷神星（由钠、铵、碳酸盐和氯离子组成）相关的假定的含有有机物的盐水在冷冻后的化学性质来探索这种基本关系，特别关注两个代表性的氨基酸（甘氨酸和天冬氨酸）和含氮脂肪族化合物（己胺）。结果表明，当急速冷冻至液氮温度时，盐水中这些有机物质的存在导致CO ₂的形成（隔离在水冰基质中）。特别地，与己胺-盐水混合物相比，这两种氨基酸产生显着更多的CO ₂ 。另一方面，慢速冷冻条件则不会表现出这种行为。通过同位素取代实验证实溶液中的碳酸氢根阴离子（而不是氨基酸本身）是CO ₂的来源。拉曼测量随后暗示了涉及氨基甲酸酯中间体形成的可能反应途径。这些结果不仅例证了有机盐相互作用在谷神星演化中的潜在重要作用，而且还为有机物的命运和海洋世界有机沉积物的未来探测策略提供了见解。