A Jupiter-class white dwarf planet should not exist where WD 1856 b sits today. Its host once swelled into a red giant that ought to have swallowed anything orbiting this close. New James Webb Space Telescope measurements, reported by NASA and published in Nature, use leftover heat to argue the world arrived late — after the star had already died.
What Webb measured on the white dwarf planet
WD 1856 b orbits the white dwarf WD 1856+534 about 80 light-years away. The planet is roughly Jupiter-sized. The remnant star is Earth-sized, so the planet is about seven times larger than its host, lead author Ryan MacDonald of the University of St. Andrews noted in the NASA briefing.
The orbit is extreme: a full circuit every 34 hours at less than 2 million miles, about 50 times closer than Earth sits to the Sun. If the planet had always lived there, the red-giant phase would have destroyed it.
During a transit, Webb found the white dwarf planet radiates at about 260°F (126°C). That is hotter than heating from the faint white dwarf alone can explain. Infrared light from the planet itself filled in part of the dip when the star was blocked.
Transit data also put the mass between about four and eleven times Jupiter’s. Starlight filtered through the atmosphere showed small cloud particles and hydrocarbons, most likely methane — the first atmospheric detection on a planet transiting a dead star, said co-author Victoria Boehm of Cornell University.
Why leftover heat rules out a red-giant swim
Two origin stories competed. One held that the planet was engulfed and somehow survived inside the dying star. The other held that gravity from companion stars in this triple system later drove an inward migration.
Co-author Christopher O’Connor of Northwestern University traced the temperature backward with cooling models. The team found no energy source today that can keep the planet this warm. The heat is residual from an earlier episode.
That heating most likely occurred 3 to 5.5 billion years after the star became a white dwarf. In that timeline, the planet stayed on a wide, safer orbit through the red-giant phase, then migrated inward later. Strong gravity near the white dwarf would have heated it during the plunge; it has been cooling ever since.
That is the Axo analysis cut: temperature is not a trivia number. It is a clock that favors late migration over an engulfment survival tale.
What this means for our solar system’s far future
In roughly five billion years, the Sun will swell into a red giant, then leave a white dwarf. Mercury, Venus, and possibly Earth face destruction. The fates of Jupiter and the outer giants are less clear.
WD 1856 b is a rare laboratory for that question. MacDonald called the result a way to look forward — a time machine for outer planets around the remnant of a Sun-like star. For readers following AXO Science, the stake is concrete: gas giants can persist after stellar death, but their final orbits may be violent rearrangements, not quiet leftovers.
Caveats and what comes next
The mass range is still wide. Cooling models carry assumptions. The migration path depends on the triple-star architecture. The methane identification is strong but not the last word on chemistry.
Boehm’s team has already observed four more Webb transits for a deeper atmospheric look. Those data should tighten composition and test whether the residual-heat clock still holds.
Until then, the July 2026 NASA–Nature package is the clearest evidence yet that a white dwarf planet can outlive its star’s death throes — if it waits far enough out, then falls in later.