HST/WFC3 Transmission Spectroscopy Of The Cold Rocky Planet TRAPPIST-1h

By Keith Cowing
March 28, 2022
Filed under
HST/WFC3 Transmission Spectroscopy Of The Cold Rocky Planet TRAPPIST-1h

TRAPPIST-1 is a nearby ultra-cool dwarf star transited by seven rocky planets. We observed three transits of its outermost planet, TRAPPIST-1h, using the G141 grism of the Wide Field Camera 3 instrument aboard the Hubble Space Telescope to place constraints on its potentially cold atmosphere.

In order to deal with the effect of stellar contamination, we model TRAPPIST-1 active regions as portions of a cooler and a hotter photosphere, and generate multi-temperature models that we compare to the out-of-transit spectrum of the star. Using the inferred spot parameters, we produce corrected transmission spectra for planet h under five transit configurations and compare these data to planetary atmospheric transmission models using the forward model CHIMERA.

Our analysis reveals that TRAPPIST-1h is unlikely to host an aerosol-free H/He-dominated atmosphere. While the current data precision limits the constraints we can put on the planetary atmosphere, we find that the likeliest scenario is that of a flat, featureless transmission spectrum in the WFC3/G141 bandpass due to a high mean molecular weight atmosphere (>1000x solar), no atmosphere, or an opaque aerosol layer, all in absence of stellar contamination.

This work outlines the limitations of modeling active photospheric regions with theoretical stellar spectra, and those brought by our lack of knowledge of the photospheric structure of ultracool dwarf stars. Further characterization of the planetary atmosphere of TRAPPIST-1h would require higher precision measurements over wider wavelengths, which will be possible with the James Webb Space Telescope.

L. J. Garcia, S. E. Moran, B. V. Rackham, H. R. Wakeford, M. Gillon, J. de Wit, N. K. Lewis

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2203.13698 [astro-ph.EP] (or arXiv:2203.13698v1 [astro-ph.EP] for this version)
Submission history
From: Lionel Garcia
[v1] Fri, 25 Mar 2022 15:12:51 UTC (7,287 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻