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🚨 New research alert 🚨 We have found an atmosphere on a planet orbiting a dead star 🔭✴️💀🪐 Our James Webb Space Telescope (JWST) observations of the white dwarf planet WD 1856b give us a preview into the fate of planets like Jupiter after the death of the Sun. 🧵⬇️ (1/10)

WD 1856b orbits a very old white dwarf, the leftover core of a star like our own Sun that died about 5.4 billion years ago. It was discovered in 2020 (Vanderburg+2020). The planet is a similar size to Jupiter, but orbits at 0.02 AU. A big mystery is how the planet survived the death of its star.

This planet is 7 times larger than its white dwarf star, so it blocks a record-breaking over 50% of the light from its white dwarf. One of our big surprises is that the planet appears to block *less* light at longer wavelength infrared light, which we explained by planetary thermal emission.

The transit spectrum we measure shows multiple 'bumps' that are best explained by methane (CH4) in the planet's atmosphere, alongside a slope at short wavelengths caused by a haze in the upper atmosphere. This is the first time we've seen the atmosphere of a close-in planet orbiting a white dwarf!

Our spectrum analysis finds that hydrocarbons (most likely methane) explains the absorption features (with an odds ratio of at least 167:1). The planet's atmosphere is also shrouded in aerosols (odds ratio at least 200,000:1). We also find the mass of the planet is about 7 Jupiter masses.