Space-based high contrast imaging mission concepts for studying rocky exoplanets in reflected light are currently under community study. We develop an inverse modeling framework to estimate the science return of such missions given different instrument design considerations. By combining an exoplanet albedo model, an instrument noise model, and an ensemble Markov chain Monte Carlo sampler, we explore retrievals of atmospheric and planetary properties for Earth twins as a function of signal-to-noise ratio (SNR) and resolution ($R$). Our forward model includes Rayleigh scattering, single-layer water clouds with patchy coverage, and pressure-dependent absorption due to water vapor, oxygen, and ozone. We simulate data at $R = 70$ and $R = 140$ from 0.4-1.0 $μ$m with SNR $ = 5, 10, 15, 20$ at 550 nm (i.e., for HabEx/LUVOIR-type instruments). At these same SNR, we simulate data for WFIRST paired with a starshade, which includes two photometric points between 0.48-0.6 $μ$m and $R = 50$ spectroscopy from 0.6-0.97 $μ$m. Given our noise model for WFIRST-type detectors, we find that weak detections of water vapor, ozone, and oxygen can be achieved with observations with at least $R = 70$ / SNR$\ = 15$, or $R = 140$ / SNR$\ = 10$ for improved detections. Meaningful constraints are only achieved with $R = 140$ / SNR$\ = 20$ data. The WFIRST data offer limited diagnostic information, needing at least SNR = 20 to weakly detect gases. Most scenarios place limits on planetary radius, but cannot constrain surface gravity and, thus, planetary mass.
Detecting and Characterizing Water Vapor in the Atmospheres of Earth Analogs through Observation of the 0.94 Micron Feature in Reflected Light
岩石类地行星的特征是未来大型地面和空间望远镜的一个重要目标。为了支持开发一个有效的观测策略，我们应用贝叶斯统计推断来解释多云的真实地球模拟物，包括在其大气水蒸气混合比的不同传播的光谱。我们专注于检测含水的世界，其大气水蒸气含量通过强0.94 $\,μ$ m H $_2$ O吸收功能，与几个观测配置。在评估行星的可居住性时，水蒸气是一个必不可少的路标，确定它的存在对于审查行星是否适合承载生命非常重要。我们发现，R=140光谱的吸收功能相结合的同相绿色光学光度点在$0.525-0.575\,μ$ m是能够区分的世界与小于$0.1\times$地球一样的水蒸气水平的世界与$1\times$地球一样的水平或更高的信噪比为5或更好的$2σ$的信心。在相同置信度下，当信噪比为10或更高时，此配置可以区分$0.01\times$和$0.1\times$类地电平。然而，即使在信噪比为15的情况下，这种配置对水蒸气混合比的强约束仍然是难以捉摸的。我们发现，添加同相光学光度点并没有显着帮助表征的H $_2$ O混合比，但使大气臭氧水平的上限。最后，我们发现，一个0.94 $\,μ$米光度点，而不是光谱，结合绿色光学点，未能产生有意义的信息，大气中的水含量。
Characterizing Earth analogs may require a moderate or high-resolution spectrograph
University of California San Diego（加州大学圣地亚哥分校）；Space Telescope Science Institute（太空望远镜科学研究所）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Department of Astronomy & Astrophysics, University of California, Santa Cruz（加州大学圣克鲁兹分校天文与天体物理系）；University of California Observatories（加州大学观测台）；Department of Astronomy, California Institute of Technology（加州理工学院天文系）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Lunar & Planetary Laboratory, University of Arizona（亚利桑那大学月球与行星实验室）
