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arXiv 2003.13107astro-ph.EP
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最常见的可居住行星II --低质量可居住行星中的咸海洋与全球气候演变

The Most Common Habitable Planets II -- Salty Oceans in Low Mass Habitable Planets and Global Climate Evolution

R. Pinotti, G. F. Porto de Mello

摘要:

可居住类地行星的全球气候演化模型没有考虑海洋盐度通过水文循环对陆地冰形成的影响。我们考虑两类这样的行星:有深海的行星,但由于热液喷口的盐去除过程较弱,因此本质上盐度较高;和有浅海的行星,在冰川作用开始期间,盐含量增加和海洋面积减少导致负反馈,有助于延缓陆地冰的扩散。我们开发了一个冰期边缘的可居住星球的玩具气候模型,使用了一系列初始盐浓度。具有深海和高盐度的行星显示出用冰盖填充北极陆地所需的时间相当长,考虑到最大盐度范围,可达23%。对于海洋较浅的行星,内在高盐度的影响被负反馈所加强,抵消了正反馈,如冰的扰动和Croll-Milankovitch扰动,在模拟的时间尺度内有效地终止了陆地冰盖的增长速度。我们还将这个模型应用于早期火星的假定海洋,发现中间结果:考虑到其冰河时代的时间尺度,盐度可能在火星气候的演变中没有发挥作用。我们的结论是,这种现象本质上是一种非生物的自我调节机制,对冰河时代,应被视为在可居住的行星比地球更小,更干燥的背景下,这很可能代表了大部分的可居住的行星。

英文摘要:

Global climate evolution models for habitable earthlike planets do not consider the effect of ocean salinity on land ice formation through the hydrological cycle. We consider two categories of such planets: planets with deep oceans, but intrinsically high salinities due to the weaker salt removal process by hydrothermal vents; and planets with shallow oceans, where the increase in salt content and decrease in ocean area during the onset of glaciation cause a negative feedback, helping delay the spread of land ice. We developed a toy climate model of a habitable planet on the verge of an ice age, using a range of initial salt concentrations. Planets with deep oceans and high salinity show considerable increase in the time necessary to fill arctic land with ice sheets, up to 23% considering the maximum salinity range. For planets with shallow oceans, the effect of intrinsic high salinity is reinforced by the negative feedback, counteracting positive feedbacks like the ice-albedo and Croll-Milankovitch perturbations, to the point of effectively terminating land ice sheet growth rate during the simulated timescale. We also apply this model to the putative ocean of early Mars, finding intermediate results: salinity probably did not play a role in the evolution of Mars' climate, considering the timescale of its ice ages. We conclude that this phenomenon is essentially an abiotic self-regulation mechanism against ice ages and should be regarded in the context of habitable planets smaller and drier than the Earth, which may well represent the bulk of habitable planets.

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