Barth Patrick, Carone Ludmila, Barnes Rory, Noack Lena, Mollière Paul, Henning Thomas
Centre for Exoplanet Science, University of St Andrews, St Andrews, UK.
SUPA, School of Physics & Astronomy, University of St Andrews, St Andrews, UK.
Astrobiology. 2021 Nov;21(11):1325-1349. doi: 10.1089/ast.2020.2277. Epub 2021 Jul 26.
Recent observations of the potentially habitable planets TRAPPIST-1 e, f, and g suggest that they possess large water mass fractions of possibly several tens of weight percent of water, even though the host star's activity should drive rapid atmospheric escape. These processes can photolyze water, generating free oxygen and possibly desiccating the planet. After the planets formed, their mantles were likely completely molten with volatiles dissolving and exsolving from the melt. To understand these planets and prepare for future observations, the magma ocean phase of these worlds must be understood. To simulate these planets, we have combined existing models of stellar evolution, atmospheric escape, tidal heating, radiogenic heating, magma-ocean cooling, planetary radiation, and water-oxygen-iron geochemistry. We present , a versatile magma-ocean evolution model, validated against the rocky super-Earth GJ 1132b and early Earth. We simulate the coupled magma-ocean atmospheric evolution of TRAPPIST-1 e, f, and g for a range of tidal and radiogenic heating rates, as well as initial water contents between 1 and 100 Earth oceans. We also reanalyze the structures of these planets and find they have water mass fractions of 0-0.23, 0.01-0.21, and 0.11-0.24 for planets e, f, and g, respectively. Our model does not make a strong prediction about the water and oxygen content of the atmosphere of TRAPPIST-1 e at the time of mantle solidification. In contrast, the model predicts that TRAPPIST-1 f and g would have a thick steam atmosphere with a small amount of oxygen at that stage. For all planets that we investigated, we find that only 3-5% of the initial water will be locked in the mantle after the magma ocean solidified.
最近对潜在宜居行星TRAPPIST - 1 e、f和g的观测表明，尽管主恒星的活动会促使大气快速逃逸，但它们仍拥有大量的水，水的质量分数可能达到几十重量百分比。这些过程会使水发生光解，产生游离氧并可能使行星干燥。行星形成后，其地幔可能完全熔融，挥发性物质在熔体中溶解和析出。为了了解这些行星并为未来的观测做准备，必须了解这些世界的岩浆海洋阶段。为了模拟这些行星，我们结合了现有的恒星演化、大气逃逸、潮汐加热、放射性加热、岩浆海洋冷却、行星辐射以及水 - 氧 - 铁地球化学模型。我们提出了一个通用的岩浆海洋演化模型，该模型已针对岩石超级地球GJ 1132b和早期地球进行了验证。我们针对一系列潮汐和放射性加热速率以及1至100个地球海洋的初始水含量，模拟了TRAPPIST - 1 e、f和g的岩浆海洋与大气的耦合演化。我们还重新分析了这些行星的结构，发现行星e、f和g的水质量分数分别为0 - 0.23、0.01 - 0.21和0.11 - 0.24。我们的模型并未对TRAPPIST - 1 e地幔固化时大气中的水和氧含量做出有力预测。相比之下，该模型预测TRAPPIST - 1 f和g在那个阶段会有一层浓厚的蒸汽大气，其中含有少量氧气。对于我们研究的所有行星，我们发现岩浆海洋固化后，只有3 - 5%的初始水会被锁定在地幔中。
