标题： 低效的水脱气抑制了岩石行星上的海洋形成：来自自洽地幔脱气模型的见解 显示英文标题

标题： Inefficient water degassing inhibits ocean formation on rocky planets: An insight from self-consistent mantle degassing models

摘要： 需要足够量的水在表面以形成水海洋。 然而，相当一部分的水在岩浆海洋固化期间仍会保留在地幔中，因此即使对于位于宜居带内的系外行星，水海洋的存在也无法保证。 为了讨论海洋形成的可能性，我们建立了两个模型，以预测岩浆海洋阶段和随后固态对流阶段的地幔脱气速率。 我们发现，具有低H$_2$O/CO$_2$比率的行星在岩浆海洋固化后可能没有足够的地表水量来形成水海洋，而且在随后的演化过程中，无论行星大小如何，大部分的水库存都会保留在地幔中。 这是因为无海洋的行星可能在停滞盖层对流下运行，而对于这些行星，亏损地幔的脱水硬化会限制地幔脱气的速率。 相反，在岩浆海洋固化期间，相当一部分的CO$_2$会已经脱气。 在强烈的温室效应下，所有地表水都会以蒸汽形式存在，水海洋可能在整个行星演化过程中都不存在。 原始硅酸盐地球中的挥发物浓度接近于形成海洋的临界量，因此如果金星具有类似的浓度，太阳辐射的小差异可能可以解释地球和金星不同的演化路径。 显示英文摘要

摘要： A sufficient amount of water is required at the surface to develop water oceans. A significant fraction of water, however, remains in the mantle during magma ocean solidification, and thus the existence of water oceans is not guaranteed even for exoplanets located in the habitable zone. To discuss the likelihood of ocean formation, we built two models to predict the rate of mantle degassing during the magma ocean stage and the subsequent solid-state convection stage. We find that planets with low H$_2$O/CO$_2$ ratios would not have a sufficient amount of surface water to develop water oceans immediately after magma ocean solidification, and the majority of the water inventory would be retained in the mantle during their subsequent evolution regardless of planetary size. This is because oceanless planets are likely to operate under stagnant lid convection, and for such planets, dehydration stiffening of the depleted lithospheric mantle would limit the rate of mantle degassing. In contrast, a significant fraction of CO$_2$ would already be degassed during magma ocean solidification. With a strong greenhouse effect, all surface water would exist as vapor, and water oceans may be absent throughout planetary evolution. Volatile concentrations in the bulk silicate Earth are close to the threshold amount for ocean formation, so if Venus shared similar concentrations, small differences in solar radiation may explain the divergent evolutionary paths of Earth and Venus.