![Best-fitting spectrum and atmospheric properties of WD 1856 b. a. Spectral decomposition illustrating the model components required to explain WD 1856 b’s JWST transmission spectrum (FIREFLy reduction; orange circles with 1 σ error bars). The best-fitting model (black curve) contains absorption from multiple CH4 features (purple shading), H2 + He continuum absorption (dark grey shading), and tentative evidence of C2H6 near 3.4 µm (brown shading) and PH3 near 4.3 µm (orange shading). Aerosol continuum opacity (silver shading) blocks thermal emission from the deep atmosphere in windows between CH4 bands, obscuring the ‘negative spikes’ that would otherwise be observed near 0.7 µm, 2.9 µm, and longwards of 4.0 µm for a clear atmosphere. The best-fitting model without nightside thermal emission (blue dashed curve) cannot explain the significantly lower transit depths longwards of 3.5 µm. b. Retrieved atmospheric properties, planetary mass, and aerosol properties from WD 1856 b’s JWST transmission spectrum for the FIREFLy (orange histograms) and Juniper (green histograms) data reductions. The median (solid line) and 1 σ credible intervals for each parameter (dashed lines) are overlaid. c. Residuals between the data and best-fitting model. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/07/Aerosols.png?fit=1200%2C678&ssl=1)
[astro-ph.EP] 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 μm spectrum reveals the presence of hydrocarbons (odds ratio of 167:1 to 5377:1, with CH4 preferred at 17:1 to 30:1), aerosols (2×105:1 to 2×106:1), and thermal emission from the planetary nightside (2×1063:1 to 2×1073:1). Our spectral analysis constrains WD 1856 b’s mass to 4.3 to 10.9MJ, finds a carbon-enriched atmosphere (with a CH4 abundance of ≈7%), and an effective temperature exceeding the expected planetary equilibrium temperature (390 to 412K vs. 160K).
Based on cooling models, these results suggest that WD 1856 b underwent a migration-related reheating event 3.0 to 5.5Gyr into the white dwarf phase, consistent with post-main-sequence tidal evolution to the present-day 0.02au circular orbit. Our results provide a window into the ultimate fate of giant planets orbiting stars with masses similar to our Sun.
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
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
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2607.01316 [astro-ph.EP](or arXiv:2607.01316v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2607.01316
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Journal reference: Nature 655, 76-80 (2026)
Related DOI:
https://doi.org/10.1038/s41586-026-10514-7
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Submission history
From: Ryan MacDonald
[v1] Wed, 1 Jul 2026 18:00:00 UTC (12,046 KB)
https://arxiv.org/abs/2607.01316
Astrobiology, Astrochemistry, Exoplanet,
