Terminator Habitability: The Case for Limited Water Availability on M-dwarf Planets
Terminator Habitability: The Case for Limited Water Availability on M-dwarf Planets
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DOI：
10.3847/1538-4357/aca970
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发表时间：
2022-12
期刊：
影响因子：
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通讯作者：
A. Lobo;Aomawa L. Shields;Igor Z. Palubski;E. Wolf
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文献类型：
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作者：
A. Lobo;Aomawa L. Shields;Igor Z. Palubski;E. Wolf
围绕M矮星运行的岩石行星是探测宜居气候最有希望和最丰富的天文目标之一。在M矮星宜居区的行星可能是同步自转的，因此我们预计会有很大的昼夜温差和可能有限的部分宜居性。以前的研究集中在部分宜居性仅限于恒星下或“眼睛”区域的情况下，但在本文中，我们探索了具有终结者宜居性的行星的可能性，其定义是在炎热的白天和冰川的夜间之间存在一个可居住的带。使用全球气候模型，我们表明，对于水资源有限的行星，由于大气能量传输减少，在终结者区域保持温和气候的同时，可能会有炎热的眼睛温度和夜间的冰冻温度。然而，在水资源丰富的行星上，增加恒星通量会增加大气能量传输，缩小昼夜温差，这样一旦白天的温度接近失控或潮湿的温室极限，终结者就不再适合居住。我们还表明，虽然水资源丰富的模拟可能会导致更大的宜居性分数，但它们很容易通过夜间表面的冷困或大气中的水蒸气逃逸而失去水分，这表明即使行星是由丰富的水资源形成的，它们的气候也可能变得水资源有限，并受到终结者宜居性的影响。
Rocky planets orbiting M-dwarf stars are among the most promising and abundant astronomical targets for detecting habitable climates. Planets in the M-dwarf habitable zone are likely synchronously rotating, such that we expect significant day–night temperature differences and potentially limited fractional habitability. Previous studies have focused on scenarios where fractional habitability is confined to the substellar or “eye” region, but in this paper we explore the possibility of planets with terminator habitability, defined by the existence of a habitable band at the transition between a scorching dayside and a glacial nightside. Using a global climate model, we show that for water-limited planets it is possible to have scorching temperatures in the “eye” and freezing temperatures on the nightside, while maintaining a temperate climate in the terminator region, due to reduced atmospheric energy transport. On water-rich planets, however, increasing the stellar flux leads to increased atmospheric energy transport and a reduction in day–night temperature differences, such that the terminator does not remain habitable once the dayside temperatures approach runaway or moist greenhouse limits. We also show that while water-abundant simulations may result in larger fractional habitability, they are vulnerable to water loss through cold trapping on the nightside surface or atmospheric water vapor escape, suggesting that even if planets were formed with abundant water, their climates could become water-limited and subject to terminator habitability.