Trends in Atmospheric Properties of Neptune-Size Exoplanets

Ian J. M. Crossfield, Laura Kreidberg
(Submitted on 31 Jul 2017)

Precise atmospheric observations have been made for a growing sample of warm Neptunes. Here we investigate the correlations between these observations and a large number of system parameters to show that, at 95% confidence, the amplitude of a warm Neptune’s spectral features in transmission scales roughly with either its equilibrium temperature (T_eq) or its bulk H/He mass fraction (f_HHe). These correlations could indicate either more optically-thick, photochemically-produced hazes at lower T_eq and/or higher-metallicity atmospheres for planets with smaller radii and lower f_HHe.

We derive an analytic relation to estimate the observing time needed with JWST/NIRISS to confidently distinguish a nominal gas giant’s transmission spectrum from a flat line. Using this tool, we show that these possible atmospheric trends could reduce the number of expected TESS planets accessible to JWST spectroscopy by up to a factor of eight. Additional observations of a larger sample of planets are required to confirm these trends in atmospheric properties as a function of planet or system quantities. If these trends can be confidently identified, the community will be well-positioned to prioritize new targets for atmospheric study and eventually break the complex degeneracies between atmospheric chemistry, composition, and cloud properties.

Comments:    8 pages, 4 figures, 2 tables, 6 planets, 2 correlations. Submitted to ApJ
Subjects:    Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as:    arXiv:1708.00016 [astro-ph.EP] (or arXiv:1708.00016v1 [astro-ph.EP] for this version)
Submission history
From: Ian Crossfield
[v1] Mon, 31 Jul 2017 18:00:26 GMT (313kb,D)
https://arxiv.org/abs/1708.00016