Atmosphere of planet WD 1856 b contains hydrocarbons and aerosols

Star system: WD 1856+534 | Distance from the Sun: 80.7 light years

White dwarfs are the dense, cooling remnants of stars like our Sun. While it is known that some planets can survive the violent evolution of their host star into a white dwarf, little is known about the makeup of their atmospheres. Observations of the planet WD 1856 b now reveal an atmosphere containing hydrocarbons and aerosols, along with unexpectedly high temperatures, offering new insights into how these planets survive and evolve long after their star has died.

Researchers used the James Webb Space Telescope to perform transmission spectroscopy, a technique that analyzes how light from the host star filters through the edges of a planet's atmosphere. By measuring which wavelengths of light are blocked, they identified chemical signatures including methane. The data also captured heat emitted from the planet's nightside.

The planet is significantly warmer than expected, with temperatures reaching up to 412 Kelvin, far above the 160 Kelvin predicted by standard equilibrium models. This suggests the planet experienced a reheating event billions of years after the host star became a white dwarf. This process is likely linked to the planet migrating inward through tidal forces to its current tight orbit.

Key findings
- Detection of hydrocarbons, including methane, and aerosols in the atmosphere of WD 1856 b.
- Mass of the planet constrained to between 4.3 and 10.9 times the mass of Jupiter.
- Atmosphere is carbon-enriched, with a methane abundance of approximately 7 percent.
- Measured planetary temperature of 390 to 412 Kelvin exceeds expected equilibrium levels.
- Evidence points to a reheating event caused by orbital migration 3 to 5.5 billion years into the white dwarf phase.

Scientific study

Aerosols and hydrocarbons in the atmosphere of a white dwarf planet (external link)