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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.

We used the NASA/ESA/CSA James Webb Space Telescope to measure the spectrum of WD 1856b during a transit event. Our goal was to measure the atmosphere of this ancient planet (that formed around 10 billion years ago) to learn what planets like Jupiter may be like after the death of the Sun.

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.

Perhaps our biggest surprise though is that the planet appears to be significantly warmer than we expected (effective temprature around 400 K). Using planet cooling models, we extrapolated back in time to find that planet must have been reheated billions of years after the star died.