Analyzing Atmospheric Temperature Profiles and Spectra of M Dwarf Rocky Planets
Analyzing Atmospheric Temperature Profiles and Spectra of M Dwarf Rocky Planets
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DOI：
10.3847/1538-4357/ab4a05
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发表时间：
2019-07
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影响因子：
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通讯作者：
M. Malik;E. Kempton;D. Koll;M. Mansfield;J. Bean;E. Kite
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作者：
M. Malik;E. Kempton;D. Koll;M. Mansfield;J. Bean;E. Kite
詹姆斯·韦伯太空望远镜（JWST）将使全面测量围绕M矮星运行的岩石系外行星的热发射光谱成为可能，从而表征其大气层。为了准备这个机会，我们提出了三个M-矮行星的模型大气层，特别适合于二次日食光谱-TRAPPIST-1b，GJ 1132 b和LHS 3844 b。使用三个限制的情况下，候选人的大气成分（纯H2O，纯CO2，和太阳丰度），我们计算的温度-压力分布和辐射-对流平衡，包括固体表面的影响的发射光谱。我们发现，大气辐射传输的显着影响冷M-星照射; H2O和CO2的吸收带在近红外线是强大的，足以吸收相当大的一部分，在低压力下的入射恒星光，这导致在高层大气中的温度反演。因此，红外线中气体不透明物的非灰带结构是一个重要因素。不透明度窗口在较高的大气温度下是静音的，所以我们预计温度反转只在足够冷的行星上才常见。我们还发现，纯CO2大气表现出较低的整体温度和较强的反射光谱相比，其他组合物的模型。我们估计，对于GJ 1132 b和LHS 3844 b，我们应该能够用JWST区分不同的大气成分。预测的温度反转的发射线目前很难测量，但未来超大望远镜的高分辨率光谱学可能能够检测到它们。
The James Webb Space Telescope (JWST) will make it possible to comprehensively measure the thermal emission spectra of rocky exoplanets orbiting M dwarfs and thus characterize their atmospheres. In preparation for this opportunity, we present model atmospheres for three M-dwarf planets particularly amenable to secondary eclipse spectroscopy—TRAPPIST-1b, GJ 1132b, and LHS 3844b. Using three limiting cases of candidate atmospheric compositions (pure H2O, pure CO2, and solar abundances) we calculate temperature–pressure profiles and emission spectra in radiative-convective equilibrium, including the effects of a solid surface. We find that the atmospheric radiative transfer is significantly influenced by the cool M-star irradiation; H2O and CO2 absorption bands in the near-infrared are strong enough to absorb a sizeable fraction of the incoming stellar light at low pressures, which leads to temperature inversions in the upper atmosphere. The non-gray band structure of gaseous opacities in the infrared is hereby an important factor. Opacity windows are muted at higher atmospheric temperatures, so we expect temperature inversions to be common only for sufficiently cool planets. We also find that pure CO2 atmospheres exhibit lower overall temperatures and stronger reflection spectra compared to models of the other compositions. We estimate that for GJ 1132b and LHS 3844b we should be able to distinguish between different atmospheric compositions with JWST. The emission lines from the predicted temperature inversions are currently hard to measure, but high-resolution spectroscopy with future extremely large telescopes may be able to detect them.