Planet by a Dead Star: Methane, Haze, and Warmth

Original: "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

arXiv:2607.01316v1 · 2026-07-01 · CC BY 4.0 · ⏱ 2 min · Exoplanets Stellar

The James Webb Space Telescope has studied the atmosphere of a planet around a white dwarf for the first time, finding methane, aerosols, and nighttime thermal emission.

Abstract

Astronomers have peered into the atmosphere of a planet orbiting a dead star—a white dwarf—for the first time. It turns out there’s methane, haze, and mysterious heat, as if the planet got a ‘second wind’ billions of years after its sun died. Will our own Jupiter one day meet the same fate?

Links in the knowledge graph 1

Imagine a tiny glowing ember from a campfire. Circling around it is an enormous hot air balloon—so large that it only covers the edge of the ember. The balloon is heated on one side, but on the other it glows quietly with warmth, and its shell gives off a faint scent. By that scent and glow, you could guess what gas the balloon is made of. This is exactly how the system works: a white dwarf—the remnant of a star like the Sun—and a giant planet giant WD 1856 b. The existence of such tiny but extremely dense stars was once predicted by Subrahmanyan Chandrasekhar.

Astronomers used the James Webb Space Telescope and the transit method as the planet passed in front of the star, to break its light into a spectrum—a rainbow that reveals which substances the light encountered on its path. For the first time, hydrocarbons were found in the planet's atmosphere—molecules made of hydrogen and carbon, including methane. The planet's atmosphere is mostly hydrogen and helium, but thanks to the methane impurities it would smell like natural gas, if we could sense it. Water vapor was barely detected, which came as a surprise too.

The heat from the planet's night side turned out to be unexpectedly strong: about 400 Kelvin (roughly 130°C), even though its equilibrium temperature is just 160 K (–113°C). It's as if the shady side of a rock by a campfire heated up nearly to the boiling point of water, even though the rock itself is far from the flames.

They also discovered aerosols—tiny particles that create a haze, similar to what appears in Earth's atmosphere after volcanic eruptions. These scatter light and make the planet's atmosphere a bit murky. All this suggests that the planet migrated closer to the star after it had become a white dwarf, and accumulated a lot of carbon. Surprisingly, its composition resembles our Neptune, only much hotter.

The study has given us a detailed portrait of a planet's atmosphere by a dead star for the very first time. This is an important step toward understanding how stellar evolution affects planets and what chemical processes take place there.

🎯 WD 1856 b is seven times larger than its star—that’s like a basketball next to a coin, rather than the other way around as in our Solar System.

T_{\rm eff} = \left( \frac{1}{\sigma_{\rm SB}} \int F_{\rm p,surf,\lambda} \, d\lambda \right)^{1/4}

Temperature of a blackbody emitting the same total power per unit surface area.

\Delta_\lambda = \frac{A_{\rm p}^{(\rm top)} - \int_{A_{\rm p}} T_\lambda \, dA}{\pi R_*^2} \times \left( \frac{1}{1 + \frac{R_{\rm p,(night),\lambda}^2}{R_*^2} \frac{F_{\rm p (night),surf,\lambda}}{F_{*,\rm surf,\lambda}}} \right)

Transmission coefficient corrected for nightside photons that dilute the star's signal.

I am the author

Planet by a Dead Star: Methane, Haze, and Warmth