This Giant Planet Survived the Death of Its Star, JWST Reveals How
Featured image: [Artist’s impression of a giant planet orbiting a white dwarf, with the planet appearing as a dark silhouette against the bright stellar remnant; credit: NASA/ESA/STScI]
A giant planet that somehow survived the violent death of its host star has finally given up its secrets. Observations from the James Webb Space Telescope, published in Nature on July 1, have revealed how the Jupiter-class world managed to endure its star’s red giant phase and end up in a blisteringly close orbit around the white dwarf remnant.
The planet, WD 1856 b, orbits the white dwarf WD 1856+534 roughly 80 light-years away in the constellation Draco. First discovered in 2020 by TESS and Spitzer, it was the first transiting planet ever found orbiting a dead star. But how it got there remained a mystery.
A planet forged in fire
The star that created WD 1856 was once Sun-like, roughly half the mass of our star. When it exhausted its nuclear fuel billions of years ago, it swelled into a red giant, engulfing any inner planets before shedding its outer layers and collapsing into an Earth-sized white dwarf, the exposed, cooling core of the original star.
WD 1856 b, a gas giant between 4 and 11 times the mass of Jupiter, somehow survived. Today it orbits the white dwarf at a distance of just 0.02 AU, about 3 million kilometers, completing an orbit every 34 hours. At that distance, the planet was almost certainly not born there, since any planet that close would have been destroyed when the star expanded.
Two competing theories emerged: either the planet was engulfed by the red giant and survived inside the star’s envelope (common envelope evolution), or it migrated inward long after the star died, pushed by gravitational interactions with other bodies.
JWST settles the debate
The key turned out to be the planet’s temperature. JWST’s NIRSpec instrument measured WD 1856 b’s atmosphere in transmission spectroscopy, detecting methane at roughly 7 percent abundance along with hints of ethane and haze particles, the first atmosphere ever detected on a planet transiting a white dwarf.
More importantly, the team led by Ryan MacDonald of the University of St Andrews measured the planet’s internal temperature at 390 to 412 Kelvin (about 126 degrees Celsius), far hotter than the roughly 160 Kelvin that white dwarf irradiation alone can explain.
By modeling cooling curves, the team determined that the planet underwent a reheating event 3.0 to 5.5 billion years into the white dwarf’s lifespan. “These results indicate that WD 1856 b underwent a migration-related reheating event,” the authors wrote. The timing rules out engulfment survival, which would have happened much earlier. Instead, the planet originally orbited much farther out and was pushed inward by gravitational interactions with two companion red dwarf stars in the system, gradually spiraling to its current orbit. The tidal forces from this migration heated the planet’s interior, producing the elevated temperature seen today.
A window into the solar system’s future
WD 1856 b offers a preview of what may await our own solar system. In roughly 5 billion years, the Sun will become a red giant, engulfing Mercury, Venus, and probably Earth. But Jupiter, orbiting at 5.2 AU, could survive, potentially migrating inward after the Sun becomes a white dwarf, just as WD 1856 b did.
The discovery also opens a new frontier for habitability studies. White dwarfs emit residual heat for trillions of years, potentially supporting life on planets that survive and migrate inward. With this atmospheric detection, astronomers have demonstrated that the chemistry of such worlds is now accessible to observation.
The paper, “Aerosols and Hydrocarbons in the Atmosphere of a White Dwarf Planet,” is published in Nature (DOI: 10.1038/s41586-026-10514-7).