雪球双稳性在中等轨道偏心率下消失
Snowball Bistability Vanishes at Moderate Orbital Eccentricity
AI总结：
研究发现，当轨道偏心率增加到0.2-0.3时，雪球双稳性消失，表明气候双稳性对行星参数的鲁棒性较低，与稀有地球假说更一致。
摘要：
雪球事件与大气中氧气增加以及地球上的生命复杂性有关，并可能对系外行星上复杂生命的发育至关重要。持续稳定的雪球事件需要雪球分支和气候双稳性，即全球冰封的雪球状态与至少有部分开放海洋的状态之间的气候双稳性。我们发现，在全球气候模型ExoCAM中，当轨道偏心率增加到0.2-0.3时，具有 slab 海洋的水行星中气候双稳性消失。这是因为随着季节性日照变化的增强，雪球状态消失，而温暖状态由于海洋的大量热容量仍保持稳定。我们使用低阶冰热力学模型表明，随着季节性增强，雪球状态消失是因为冰自保温导致冬季冰底冻结相对夏季冰顶融化减少。结合先前研究显示，围绕低质量恒星和自转周期较长的行星上，雪球气候双稳性减少，而潮汐锁定行星上完全消失，我们的研究表明，雪球气候双稳性可能不像以前认为的那样对行星参数具有鲁棒性，代表了与稀有地球假说更为一致的宜居性方面，而非柯比恩原理。
英文摘要：
Snowball episodes are associated with increases in atmospheric oxygen and the complexity of life on Earth, and they may be essential for the development of complex life on exoplanets. Sustained, stable Snowball episodes require a Snowball bifurcation and climate bistability between the globally ice-covered Snowball state and a state with at least some open ocean. We find that climate bistability disappears for an aquaplanet with a slab ocean in the global climate model ExoCAM when the orbital eccentricity is increased to 0.2-0.3. This happens because the Snowball state ceases to exist as seasonal insolation variations intensify, while the warm state remains stable due to the ocean's large heat capacity. We use a low-order ice-thermodynamic model to show that the Snowball state ceases to exist as seasonality increases because winter freezing at the ice bottom is reduced relative to summer melting at the ice top due to ice self-insulation. Combined with previous research showing that Snowball climate bistability diminishes for planets orbiting low-mass stars and ones with longer rotation periods, and that it disappears entirely for tidally locked planets, our work suggests that the Snowball climate bistability may not be as robust to planetary parameters as previously thought, representing one aspect of habitability more consistent with the rare Earth hypothesis than the Copernican principle.
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