Hydrohalite Salt-albedo Feedback Could Cool M-dwarf Planets
Hydrohalite Salt-albedo Feedback Could Cool M-dwarf Planets
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DOI：
10.3847/1538-4357/aadcaa
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发表时间：
2018-08
期刊：
影响因子：
--
通讯作者：
Aomawa L. Shields;R. Carns
中科院分区：
文献类型：
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作者：
Aomawa L. Shields;R. Carns
在m矮行星的环境中可能形成的一种表面类型是氯化钠二水合物，或“水盐岩”（NaCl·2H2O），它可以在低温下沉淀在裸露的海冰中。与无盐水冰不同，水盐岩在近红外波段具有很强的反射率，而m矮星在近红外波段发射强烈，这使得水盐岩与m矮星光谱能量分布之间相互作用的影响有必要量化。利用三维全球气候模型，首次探索了水盐岩诱导的盐反照率反馈在系外行星上的气候效应。在固定的CO2条件下，快速旋转的宜居带m矮行星从其主星接收到65%或更少的现代太阳常数，当气候模拟中包括水盐岩的反照率参数化时，与没有这种参数化的模拟相比，温度更低。在有和没有这种参数化的情况下，全球平均表面温度的差异随着安装的降低而增加，这可能会增加具有活性碳循环的行星上宜居条件的二氧化碳积累要求。同步旋转的宜居带m矮行星在较高的安装水平（现代太阳常数的90%或更少）比具有类似地球的旋转周期的行星更容易受到盐反照率反馈，因为它们的最低日侧温度更低。这些水盐岩似乎与最近发现的几个可能适合居住的m矮行星最相关，包括比邻星b、TRAPPIST-1e和LHS 1140b，这使得水盐岩的反照率参数化在未来的气候模拟中具有直接重要性。
A possible surface type that may form in the environments of M-dwarf planets is sodium chloride dihydrate, or “hydrohalite” (NaCl · 2H2O), which can precipitate in bare sea ice at low temperatures. Unlike salt-free water ice, hydrohalite is highly reflective in the near-infrared, where M-dwarf stars emit strongly, making the effect of the interaction between hydrohalite and the M-dwarf spectral energy distribution necessary to quantify. We carried out the first exploration of the climatic effect of hydrohalite-induced salt-albedo feedback on extrasolar planets, using a three-dimensional global climate model. Under fixed CO2 conditions, rapidly rotating habitable-zone M-dwarf planets receiving 65% or less of the modern solar constant from their host stars exhibit cooler temperatures when an albedo parameterization for hydrohalite is included in climate simulations, compared to simulations without such a parameterization. Differences in global mean surface temperature with and without this parameterization increase as the instellation is lowered, which may increase CO2 build-up requirements for habitable conditions on planets with active carbon cycles. Synchronously rotating habitable-zone M-dwarf planets appear susceptible to salt-albedo feedback at higher levels of instellation (90% or less of the modern solar constant) than planets with Earth-like rotation periods, due to their cooler minimum dayside temperatures. These instellation levels where hydrohalite seems most relevant correspond to several recently discovered potentially habitable M-dwarf planets, including Proxima Centauri b, TRAPPIST-1e, and LHS 1140b, making an albedo parameterization for hydrohalite of immediate importance in future climate simulations.