H2-dominated Atmosphere as an Indicator of Second-generation Rocky White Dwarf Exoplanets

Zifan Lin, Sara Seager, Sukrit Ranjan, Thea Kozakis, Lisa Kaltenegger

Following the discovery of the first exoplanet candidate transiting a white dwarf (WD), a “white dwarf opportunity” for characterizing the atmospheres of terrestrial exoplanets around WDs is emerging. Large planet-to-star size ratios and hence large transit depths make transiting WD exoplanets favorable targets for transmission spectroscopy – conclusive detection of spectral features on an Earth-like planet transiting a close-by WD can be achieved within a medium James Webb Space Telescope (JWST) program. Despite the apparently promising opportunity, however, the post-main sequence (MS) evolutionary history of a first-generation WD exoplanet has never been incorporated in atmospheric modeling. Furthermore, second-generation planets formed in WD debris disks have never been studied from a photochemical perspective. We demonstrate that transmission spectroscopy can identify a second-generation rocky WD exoplanet with a thick (∼1 bar) H2-dominated atmosphere. In addition, we can infer outgassing activities of a WD exoplanet based on its transmission spectra and test photochemical runaway by studying CH4 buildup.

Comments: 25 pages, 10 figures, 3 tables, accepted for publication in ApJ Letters

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Cite as: arXiv:2201.08529 [astro-ph.EP] (or arXiv:2201.08529v1 [astro-ph.EP] for this version)

Submission history

From: Zifan Lin 

[v1] Fri, 21 Jan 2022 03:44:52 UTC (9,316 KB)

https://arxiv.org/abs/2201.08529

Astrobiology