Jupiter-Sized Planet Survives Its Star’s Death: First Atmosphere Detected Around a White Dwarf

Astronomers used the James Webb Space Telescope (JWST) to obtain transmission spectra of the gas giant WD 1856 b as it transited its white dwarf host WD 1856+534. The spectra reveal hydrocarbons—most plausibly methane—accounting for roughly 7 % of the atmosphere, together with a haze of small cloud particles and thermal emission from the planet’s night side. This marks the first confirmed detection of an atmosphere on a planet orbiting a white dwarf.

Giant Exoplanet around White Dwarf May Reveal Jupiter’s Fate Billions of Years from NowA Jupiter-sized planet outlived its dying star, and NASA’s Webb has now read its atmosphere — the first ever detected on a world orbiting a white dwarfEarth & Sky

WD 1856+534 is a cooling white dwarf, the dense Earth-sized remnant of a Sun-like star that exhausted its nuclear fuel, expanded into a red giant, and shed its outer layers about six billion years ago. The system lies ? 80 light-years away in Draco. WD 1856 b, discovered in 2020 by NASA’s TESS and the Spitzer Space Telescope, orbits the white dwarf every 34 hours at a distance ? 0.02 AU—about fifty times closer than Earth’s orbit around the Sun. At such proximity, a planet would have been expected to be engulfed during the red-giant phase.

Earth & SkyGiant Exoplanet around White Dwarf May Reveal Jupiter’s Fate Billions of Years from NowA Jupiter-sized planet outlived its dying star, and NASA’s Webb has now read its atmosphere — the first ever detected on a world orbiting a white dwarf

• Radius: 0.9 × Jupiter’s radius (? seven times the white dwarf’s radius).

Giant Exoplanet around White Dwarf May Reveal Jupiter’s Fate Billions of Years from Now

• Mass: estimated between 4.3 and 10.9 Jupiter masses.

Giant Exoplanet around White Dwarf May Reveal Jupiter’s Fate Billions of Years from Now

• Orbital period: 34 hours; semi-major axis ? 2 million mi (3 million km).

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• Measured atmospheric temperature: ? 390–412 K (? 126 °C, 260 °F), far above the ? 160 K expected from stellar heating alone.

A Jupiter-sized planet outlived its dying star, and NASA’s Webb has now read its atmosphere — the first ever detected on a world orbiting a white dwarf

• Atmospheric composition: hydrocarbons (most likely methane) and aerosol haze; infrared data indicate night-side thermal emission.

A Jupiter-sized planet outlived its dying star, and NASA’s Webb has now read its atmosphere — the first ever detected on a world orbiting a white dwarf

Lead author Ryan MacDonald (University of St Andrews) emphasized that the detection provides a “window into the ultimate fate of giant planets orbiting stars with masses similar to our Sun.” Co-author Victoria Boehm (Cornell University) highlighted the novelty of observing an atmosphere on a planet transiting a dead star. Northwestern University researcher Christopher O’Connor described modeling the planet’s cooling history to infer a heating event 3–5.5 billion years after the white dwarf formed.

Giant Exoplanet around White Dwarf May Reveal Jupiter’s Fate Billions of Years from Now

The authors acknowledge two competing scenarios for the planet’s present orbit: (1) survival of a red-giant engulfment, possibly within the stellar envelope, and (2) post-white-dwarf inward migration driven by gravitational interactions with the system’s two companion stars. The mass estimate spans a range that approaches the brown-dwarf boundary, and the spectral data favor hydrocarbons in general but cannot definitively confirm methane. These uncertainties temper definitive conclusions about the planet’s evolutionary path.

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• Mass: reported as 4.3–10.9 Jupiter masses, leaving the exact classification ambiguous.

Giant Exoplanet around White Dwarf May Reveal Jupiter’s Fate Billions of Years from Now

• Composition: spectra indicate hydrocarbons; the most probable molecule is methane, but the identification is not conclusive.

A Jupiter-sized planet outlived its dying star, and NASA’s Webb has now read its atmosphere — the first ever detected on a world orbiting a white dwarf

• Formation scenario: timing of the heating event suggests migration, yet the alternative engulfment hypothesis remains viable.

A Jupiter-sized planet outlived its dying star, and NASA’s Webb has now read its atmosphere — the first ever detected on a world orbiting a white dwarf

The system offers a concrete example of a giant planet persisting after its host star’s death, informing models of planetary survival and migration in post-main-sequence environments. By analogy, the result provides a test case for predictions about the distant future of the Solar System’s outer planets when the Sun becomes a white dwarf.

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• “The planet is about the size of Jupiter, but the white dwarf it orbits is the size of Earth, so the planet is seven times larger than its star,” — Ryan MacDonald, Lead author, University of St Andrews

A Jupiter-sized planet outlived its dying star, and NASA’s Webb has now read its atmosphere — the first ever detected on a world orbiting a white dwarf

• “Co-author Victoria Boehm of Cornell University said: We saw the telltale signatures of small cloud particles and hydrocarbons, most likely methane, which is the first time we have seen an atmosphere on a planet transiting a dead star.” — Victoria Boehm, Co-author, Cornell University

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• “The big question is how WD 1856 b ended up where it is today, and there are two theories. One is that the planet was swallowed by the host star as it was dying, and managed to survive on the inside. The other is that migration took place due to the gravitational effect of other objects in the system. The white dwarf is part of a triple star system, and the companion stars could have influenced WD 1856 b’s orbit.” — Christopher O’Connor, Northwestern University

A Jupiter-sized planet outlived its dying star, and NASA’s Webb has now read its atmosphere — the first ever detected on a world orbiting a white dwarf

• “We’re used to looking back in time when we use telescopes, but this is the first time we have been able to look forward to what might happen to the outer planets around the remnant of a Sun-like star,” — Ryan MacDonald

Giant Exoplanet around White Dwarf May Reveal Jupiter’s Fate Billions of Years from Now

The team has recorded four additional JWST transits of WD 1856 b to refine measurements of its atmospheric chemistry and haze properties. Continued monitoring will test the migration hypothesis and improve constraints on the planet’s mass and thermal evolution.

Giant Exoplanet around White Dwarf May Reveal Jupiter’s Fate Billions of Years from Now