The Featureless HST/WFC3 Transmission Spectrum of the Rocky Exoplanet GJ 1132b: No Evidence for a Cloud-free Primordial Atmosphere and Constraints on Starspot Contamination
The Featureless HST/WFC3 Transmission Spectrum of the Rocky Exoplanet GJ 1132b: No Evidence for a Cloud-free Primordial Atmosphere and Constraints on Starspot Contamination
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DOI：
10.3847/1538-3881/ac75de
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发表时间：
2021-05
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通讯作者：
J. Libby-Roberts;Z. Berta-Thompson;Hannah Diamond-Lowe;M. Gully-Santiago;J. Irwin;E. Kempton;B. Rackham;D. Charbonneau;J. Désert;J. Dittmann;R. Hofmann;C. Morley;E. Newton
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作者：
J. Libby-Roberts;Z. Berta-Thompson;Hannah Diamond-Lowe;M. Gully-Santiago;J. Irwin;E. Kempton;B. Rackham;D. Charbonneau;J. Désert;J. Dittmann;R. Hofmann;C. Morley;E. Newton
围绕着一颗距离我们12秒差距的M矮星运行的系外行星GJ 1132b是透射光谱学的主要目标。质量为1.7 M，半径为1.1 R，体积密度表明这颗行星是岩石行星。然而，在580 K的平衡温度下，GJ 1132 b可能仍然保留了一些大气层的外观。了解这种大气层是否存在及其组成对于了解绕M矮星运行的类地行星的大气层如何演变至关重要。利用哈勃空间望远镜（HST）的WFC 3（Wide Field Camera 3）观测了GJ 1132 b的5次凌日。我们发现了一个从1.1到1.7 μ m的无特征透射光谱，排除了无云大气的金属丰度为4.8 σ的置信度。我们将联合收割机的WFC 3结果与TESS和档案宽带和光谱观测的过境深度相结合，找到了0.7至4.5 μ m的无特征光谱。因此，GJ 1132b具有高平均分子量的大气，具有高海拔气溶胶层，或者实际上没有大气。为了区分这些可能性，需要更高精度的观测。我们探讨了热和冷的恒星黑子对观测到的透射光谱GJ 1132b的影响，量化了斑点引起的过境深度特征的幅度。使用一个简单的泊松模型，我们估计点的温度对比，点覆盖率，和斑点大小GJ 1132。这些限制，以及建模框架，可能是有用的GJ 1132 b或其他行星过境类似的不活跃的M矮星的未来观测。
Orbiting an M dwarf 12 pc away, the transiting exoplanet GJ 1132b is a prime target for transmission spectroscopy. With a mass of 1.7 M ⊕ and radius of 1.1 R ⊕, GJ 1132b’s bulk density indicates that this planet is rocky. Yet with an equilibrium temperature of 580 K, GJ 1132b may still retain some semblance of an atmosphere. Understanding whether this atmosphere exists and its composition will be vital for understanding how the atmospheres of terrestrial planets orbiting M dwarfs evolve. We observe five transits of GJ 1132b with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). We find a featureless transmission spectrum from 1.1 to 1.7 μm, ruling out cloud-free atmospheres with metallicities 4.8σ confidence. We combine our WFC3 results with transit depths from TESS and archival broadband and spectroscopic observations to find a featureless spectrum across 0.7 to 4.5 μm. GJ 1132b therefore has a high mean molecular weight atmosphere, possesses a high-altitude aerosol layer, or has effectively no atmosphere. Higher-precision observations are required in order to differentiate between these possibilities. We explore the impact of hot and cold starspots on the observed transmission spectrum GJ 1132b, quantifying the amplitude of spot-induced transit depth features. Using a simple Poisson model, we estimate spot temperature contrasts, spot covering fractions, and spot sizes for GJ 1132. These limits, as well as the modeling framework, may be useful for future observations of GJ 1132b or other planets transiting similarly inactive M dwarfs.