Aerosols and hydrocarbons in the atmosphere of a white dwarf planet
Ryan J. MacDonald, Christopher E. O'Connor, Victoria A. Boehm, E. M. May, David K. Sing, Elijah Mullens, L. C. Mayorga, Trevor O. Foote, Simon Blouin, Logan A. Pearce, Nikole K. Lewis, Jeff Valenti, Natasha E. Batalha, Maura Lally, Joshua D. Lothringer, Mark S. Marley, Ishan Mishra, Susan E. Mullally
astro-ph.EP, astro-ph.SR
Submitted: 2026-07-01
Comments: 28 pages, 12 figures, 3 tables. Published in Nature (1 July 2026). Accepted manuscript, for the version of record see: https://www.nature.com/articles/s41586-026-10514-7
Journal ref: Nature 655, 76-80 (2026)
DOI: 10.1038/s41586-026-10514-7
Code: https://github.com/lkreidberg/batman
License: http://creativecommons.org/licenses/by/4.0/
The gist: Most stars, including our Sun, will one day evolve into red giants and, subsequently, white dwarfs.
Terminology
Abstract
Most stars, including our Sun, will one day evolve into red giants and, subsequently, white dwarfs. Several planet candidates have recently been identified orbiting white dwarfs, demonstrating that planets can survive the stellar post-main-sequence stage intact. Little is known about the atmospheric composition of post-main-sequence planets, with the most evolved transiting planets with atmospheric detections to date orbiting subgiants. Here we report an atmospheric detection for the white dwarf planet WD 1856 b, achieved through transmission spectroscopy with the JWST NIRSpec PRISM. Our 0.5-5.0 mu m spectrum reveals the presence of hydrocarbons (odds ratio of 167:1 to 5377:1, with CH 4 preferred at 17:1 to 30:1), aerosols (2 times 10 5:1 to 2 times 10 6:1), and thermal emission from the planetary nightside (2 times 10 63:1 to 2 times 10 73:1). Our spectral analysis constrains WD 1856 b's mass to 4.3 to 10.9 M J, finds a carbon-enriched atmosphere (with a CH 4 abundance of about 7%), and an effective temperature exceeding the expected planetary equilibrium temperature (390 to 412, K vs. 160, K). Based on cooling models, these results suggest that WD 1856 b underwent a migration-related reheating event 3.0 to 5.5, Gyr into the white dwarf phase, consistent with post-main-sequence tidal evolution to the present-day 0.02, au circular orbit. Our results provide a window into the ultimate fate of giant planets orbiting stars with masses similar to our Sun.
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