Low Hesperian PCO2 constrained from in situ mineralogical analysis at Gale Crater, Mars
Low Hesperian PCO2 constrained from in situ mineralogical analysis at Gale Crater, Mars
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DOI：
10.1073/pnas.1616649114
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发表时间：
2017-02-28
影响因子：
11.1
通讯作者：
Vasavada, Ashwin R.
中科院分区：
文献类型：
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作者：
Bristow, Thomas F.;Haberle, Robert M.;Vasavada, Ashwin R.
在火星气候模型中，二氧化碳是一种重要的大气成分，这些模型试图将微弱的年轻太阳与诺亚纪和早期西方纪的液态水证据相协调。在这项研究中，我们使用矿物和上下文的沉积环境数据测量的火星科学实验室（MSL）漫游车Currency估计大气中的二氧化碳分压（PCO2）符合一个长期存在的湖泊系统在盖尔陨石坑在类似的3.5 Ga。一个反应传输模型，模拟矿物学观察内羊床成员在耶洛奈夫湾（YKB），通过耦合矿物平衡与碳酸盐沉淀动力学和沉积速率，表明大气中的PCO2水平在10毫巴范围内。在如此低的二氧化碳分压水平下，现有的气候模型无法将西方火星的温度提高到接近水的冰点，需要其他气体来提高大气压力，以防止湖泊沃茨流失到大气中。因此，要么盖尔的湖泊特征是在寒冷的环境中形成的，其形成机制尚待确定，要么气候模型仍然缺乏一个重要的组成部分，可以提高西方火星的表面温度，至少在当地是这样。我们的研究结果也施加限制的潜在作用，大气中的二氧化碳推断温暖的条件和山谷网络形成的晚诺亚纪。
Carbon dioxide is an essential atmospheric component in martian climate models that attempt to reconcile a faint young sun with planetwide evidence of liquid water in the Noachian and Early Hesperian. In this study, we use mineral and contextual sedimentary environmental data measured by the Mars Science Laboratory (MSL) Rover Curiosity to estimate the atmospheric partial pressure of CO2 (PCO2) coinciding with a long-lived lake system in Gale Crater at similar to 3.5 Ga. A reaction-transport model that simulates mineralogy observed within the Sheepbed member at Yellowknife Bay (YKB), by coupling mineral equilibria with carbonate precipitation kinetics and rates of sedimentation, indicates atmospheric PCO2 levels in the 10s mbar range. At such low PCO2 levels, existing climate models are unable to warm Hesperian Mars anywhere near the freezing point of water, and other gases are required to raise atmospheric pressure to prevent lake waters from being lost to the atmosphere. Thus, either lacustrine features of Gale formed in a cold environment by a mechanism yet to be determined, or the climatemodels still lack an essential component that would serve to elevate surface temperatures, at least locally, on Hesperian Mars. Our results also impose restrictions on the potential role of atmospheric CO2 in inferred warmer conditions and valley network formation of the late Noachian.