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arXiv 2005.13002astro-ph.EPastro-ph.SR
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不同恒星光谱对潮汐锁定类地系外行星气候的影响

Implications of different stellar spectra for the climate of tidally-locked Earth-like exoplanets

Jake K. Eager, David J. Reichelt, Nathan J. Mayne, F. Hugo Lambert, Denis E. Sergeev, Robert J. Ridgway, James Manners, Ian A. Boutle, Timothy M. Lenton, Krisztian Kohary

摘要:

大多数潜在的可居住的系外行星探测到的轨道比太阳冷的恒星,因此被恒星光谱照射,其峰值波长比入射到地球上的波长更长。在这里,我们提出的结果,从一组模拟的潮汐锁定的类地行星轨道三个不同的主机恒星隔离模拟气候的恒星光谱的影响。具体来说,我们进行模拟的基础上TRAPPIST-1 e,采用类似地球的大气层,并使用英国气象局统一模型在一个理想化的“水行星”的配置。同时保持行星参数不变,包括总恒星通量(900 W/m $^2$)和轨道周期(6.10地球日),我们比较模拟的恒星光谱是一个静止的TRAPPIST-1,比邻星和太阳之间的结果。与表面相比,与较冷的宿主恒星相比,对流层直接吸收的入射恒星辐射的比例增加。这反过来又导致对流的稳定性增加,白天总云层覆盖率减少(减少散射),导致地面温度升高。对流层直接加热的增加也导致了从昼侧到夜侧的更有效的热量传输,因此,昼夜温度对比度降低。我们推断,具有类似地球的大气层的行星绕较冷的恒星运行,具有较低的昼侧云层覆盖率,与绕较热的恒星运行的类似行星相比,在给定的行星旋转速率下,在增加的轨道半径下可能允许宜居条件。

英文摘要:

The majority of potentially habitable exoplanets detected orbit stars cooler than the Sun, and therefore are irradiated by a stellar spectrum peaking at longer wavelengths than that incident on Earth. Here, we present results from a set of simulations of tidally-locked terrestrial planets orbiting three different host stars to isolate the effect of the stellar spectra on the simulated climate. Specifically, we perform simulations based on TRAPPIST-1e, adopting an Earth-like atmosphere and using the UK Met Office Unified Model in an idealised 'aqua-planet' configuration. Whilst holding the planetary parameters constant, including the total stellar flux (900 W/m$^2$) and orbital period (6.10 Earth days), we compare results between simulations where the stellar spectrum is that of a quiescent TRAPPIST-1, Proxima Centauri and the Sun. The simulations with cooler host stars had an increased proportion of incident stellar radiation absorbed directly by the troposphere compared to the surface. This, in turn, led to an increase in the stability against convection, a reduction in overall cloud coverage on the dayside (reducing scattering), leading to warmer surface temperatures. The increased direct heating of the troposphere also led to more efficient heat transport from the dayside to the nightside and, therefore, a reduced day-night temperature contrast. We inferred that planets with an Earth-like atmosphere orbiting cooler stars had lower dayside cloud coverage, potentially allowing habitable conditions at increased orbital radii, compared to similar planets orbiting hotter stars for a given planetary rotation rate.

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