Reflected Spectroscopy Of Small Exoplanets I: Determining The Atmospheric Composition Of sub-Neptunes Planets

Reflected light spectra of a hypothetical H2-H2O atmosphere with different amount of water. When water is below 10−2 in volume mixing ratio the spectra are distinguishable, while above 10−2 the spectra are degenerate and not sensitive anymore to the volume mixing ratio of the two gases.

Direct imaging of widely separated exoplanets from space will obtain their reflected light spectra and measure their atmospheric properties, and small and temperate planets will be the focus of the next generation telescopes.

In this work, we used our Bayesian retrieval algorithm ExoReLℜ to determine the constraints on the atmospheric properties of sub-Neptune planets from observations taken with a HabEx-like telescope. Small and temperate planets may have a non-H2-dominated atmosphere, and therefore, we introduced the compositional analysis technique in our framework to explore the bulk atmospheric chemistry composition without any prior knowledge about it.

We have developed a novel set of prior functions for the compositional analysis free parameters. We compared the performances of the framework with the flat prior and the novel prior and we reported a better performance when using the novel priors set. We found that the retrieval algorithm can not only identify the dominant gas of the atmosphere but also to constraint other less abundant gases with high statistical confidence without any prior information on the composition.

The results presented here demonstrates that reflected light spectroscopy can characterize small exoplanets with diverse atmospheric composition. The Bayesian framework should be applied to design the instrument and the observation plan of exoplanet direct imaging experiments in the future.

Mario Damiano, Renyu Hu

Comments: 16 pages, 12 figures, 4 tables, accepted for publication in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2109.11659 [astro-ph.EP] (or arXiv:2109.11659v1 [astro-ph.EP] for this version)
Submission history
From: Mario Damiano
[v1] Thu, 23 Sep 2021 21:46:22 UTC (3,161 KB)

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