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arXiv 2004.09076astro-ph.EP
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早期火星变暖与气候循环:CO2-H2碰撞诱导吸收的影响

Warming Early Mars with Climate Cycling: The Effect of CO2-H2 Collision-induced Absorption

Benjamin P. C. Hayworth, Ravi Kumar Kopparapu, Jacob Haqq-Misra, Natasha E. Batalha, Rebecca C. Payne, Bradford J. Foley, Mma Ikwut-Ukwa, James F. Kasting

摘要:

解释早期火星表面存在液态水的证据对气候建模者来说是一个挑战,因为在诺亚纪晚期,太阳的亮度降低了30%。我们建议,额外的温室效应迫使CO2-H2碰撞引起的吸收是能够使地面温度以上冻结,并可以把早期的火星进入一个有限的循环制度。极限循环发生时,日照低,CO2出气率无法平衡与CO2的快速下降在温暖的风化期。处于这种状态的行星将在全球冰川和短暂的温暖气候阶段之间交替。这一机制能够解释火星记录中短暂温暖期的地貌证据。先前的研究表明,碰撞引起的CO2-H2吸收能够使早期火星冰川消退,但只有在高H2释气率(大于600 Tmol/年)和高表面压力(3至4巴)的情况下。我们使用新的理论推导的碰撞引起的吸收系数CO2-H2重新评估早期火星的气候极限循环假设。使用新的和更强的吸收系数在我们的1维辐射对流模型以及我们的能量平衡模型,我们发现,极限循环可以发生与H2放气率低至~300 Tmol/年,在表面压力低于3巴。我们的结果更接近早期火星表面压力和氢丰度的古参数。

英文摘要:

Explaining the evidence for surface liquid water on early Mars has been a challenge for climate modelers, as the sun was ~30% less luminous during the late-Noachian. We propose that the additional greenhouse forcing of CO2-H2 collision-induced absorption is capable of bringing the surface temperature above freezing and can put early Mars into a limit-cycling regime. Limit cycles occur when insolation is low and CO2 outgassing rates are unable to balance with the rapid drawdown of CO2 during warm weathering periods. Planets in this regime will alternate between global glaciation and transient warm climate phases. This mechanism is capable of explaining the geomorphological evidence for transient warm periods in the martian record. Previous work has shown that collision-induced absorption of CO2-H2 was capable of deglaciating early Mars, but only with high H2 outgassing rates (greater than ~600 Tmol/yr) and at high surface pressures (between 3 to 4 bars). We used new theoretically derived collision-induced absorption coefficients for CO2-H2 to reevaluate the climate limit cycling hypothesis for early Mars. Using the new and stronger absorption coefficients in our 1-dimensional radiative convective model as well as our energy balance model, we find that limit cycling can occur with an H2 outgassing rate as low as ~300 Tmol/yr at surface pressures below 3 bars. Our results agree more closely with paleoparameters for early martian surface pressure and hydrogen abundance.

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