![Left: Orbital separations of inspiralling planets over time. Right: Mass accreted onto planets over time. For each initial planet mass, we show results for 𝜀 ∈ [0.01, 0.1, 0.3, 0.5, 1.0], with an increasing efficiency denoted by an increasing opacity. We also allow the accretion to increase up to 10× the Eddington limit, denoted by the dotted lines. Accretion stops when 𝑅𝐵 < 𝑅Jup (see §2.3). -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/08/Atmospheric-Signatures.png?fit=1200%2C687&ssl=1)
[astro-ph.EP] The majority of confirmed exoplanets orbit within 1 au of a main-sequence (MS) star. When their stellar hosts evolve off the MS, many of these planets will be engulfed and destroyed, creating empty “forbidden” zones around the stars as they evolve to their final state as a white dwarf (WD).
However, several confirmed and candidate WD planets have been found within this forbidden zone. Two formation scenarios have been proposed to explain the existence of these close-in planets: high-eccentricity migration and common envelope evolution (CEE). There are currently few observational tests to distinguish between these pathways.
In this study, we investigate whether CEE could leave a detectable atmospheric signature. Using Modules for Experiments in Stellar Astrophysics (MESA) models, we simulate an engulfed planet inspiraling into an AGB star, and allow the planet to accrete mass via Bondi-Hoyle-Lyttleton accretion.
Assuming a range of planet masses (1−13 MJup) and accretion efficiencies (0.01−1.0), we find that the planet can accrete up to 48% of its initial mass in the most extreme Eddington-limited scenario. Because this accreted material is enriched in hydrogen and helium, we expect it to decrease the planet’s bulk metallicity.
Using simulated emission spectra, we find that CEE can increase thermal emission by up to 9.0% for a cool planet such as WD 1856 b. For lower accretion efficiencies (0.01−0.5), thermal emission increases between 0.1−3.6%. This signature may be observable in the most favorable cases, providing a potential new probe for investigating the dynamical history of close-in planets around WDs.
Sydney Jenkins, Andrew Vanderburg, James Mang, Juliette Becker, Caroline V. Morley, Melinda Soares-Furtado, Ricardo Yarza
Comments: 16 pages, 5 figures, 3 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2607.28717 [astro-ph.EP] (or arXiv:2607.28717v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2607.28717
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Journal reference: ApJ 1006, 241 (2026)
Related DOI:
https://doi.org/10.3847/1538-4357/ae83b5
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Submission history
From: Sydney Jenkins
[v1] Thu, 30 Jul 2026 18:00:00 UTC (2,158 KB)
https://arxiv.org/abs/2607.28717
Astrobiology,
