Venkatesan Vidya, Shields Aomawa L, Deitrick Russell, Wolf Eric T, Rushby Andrew
Department of Physics and Astronomy, University of California, Irvine, California, USA.
School of Earth and Ocean Sciences, University of Victoria, Victoria, Canada.
Astrobiology. 2025 Jan;25(1):42-59. doi: 10.1089/ast.2023.0103. Epub 2025 Jan 14.
Eccentric planets may spend a significant portion of their orbits at large distances from their host stars, where low temperatures can cause atmospheric CO to condense out onto the surface, similar to the polar ice caps on Mars. The radiative effects on the climates of these planets throughout their orbits would depend on the wavelength-dependent albedo of surface CO ice that may accumulate at or near apoastron and vary according to the spectral energy distribution of the host star. To explore these possible effects, we incorporated a CO ice-albedo parameterization into a one-dimensional energy balance climate model. With the inclusion of this parameterization, our simulations demonstrated that F-dwarf planets require 29% more orbit-averaged flux to thaw out of global water ice cover compared with simulations that solely use a traditional pure water ice-albedo parameterization. When no eccentricity is assumed, and host stars are varied, F-dwarf planets with higher bond albedos relative to their M-dwarf planet counterparts require 30% more orbit-averaged flux to exit a water snowball state. Additionally, the intense heat experienced at periastron aids eccentric planets in exiting a snowball state with a smaller increase in instellation compared with planets on circular orbits; this enables eccentric planets to exhibit warmer conditions along a broad range of instellation. This study emphasizes the significance of incorporating an albedo parameterization for the formation of CO ice into climate models to accurately assess the habitability of eccentric planets, as we show that, even at moderate eccentricities, planets with Earth-like atmospheres can reach surface temperatures cold enough for the condensation of CO onto their surfaces, as can planets receiving low amounts of instellation on circular orbits.
偏心行星在其轨道的很大一部分时间里可能远离其主恒星，在那里低温会导致大气中的一氧化碳凝结到表面，类似于火星上的极地冰盖。这些行星在整个轨道上对气候的辐射效应将取决于可能在远日点或其附近积累的表面一氧化碳冰的波长依赖反照率，并根据主恒星的光谱能量分布而变化。为了探索这些可能的影响，我们将一氧化碳冰反照率参数化纳入了一维能量平衡气候模型。通过纳入这个参数化，我们的模拟表明，与仅使用传统纯水冰反照率参数化的模拟相比，F型矮行星要融化全球水冰覆盖需要多29%的轨道平均通量。在不假设偏心率且改变主恒星的情况下，相对于M型矮行星对应体具有更高邦德反照率的F型矮行星要脱离水雪球状态需要多30%的轨道平均通量。此外，近日点经历的强烈热量有助于偏心行星以比圆形轨道上的行星更小的辐射增加量脱离雪球状态；这使得偏心行星在广泛的辐射范围内表现出更温暖的条件。这项研究强调了将一氧化碳冰形成的反照率参数化纳入气候模型以准确评估偏心行星宜居性的重要性，因为我们表明，即使在中等偏心率下，具有类似地球大气层的行星也能达到足够低的表面温度，使一氧化碳凝结到其表面，接受低辐射量的圆形轨道上的行星也是如此。
