James Webb Space Telescope (JWST) observations have revealed that the fate of planets after the death of their host star may be surprisingly warm, according to new research from the University of St Andrews.
The JWST observations offer a possible glimpse into what our solar system will be like billions of years from now, particularly for gas giants like Jupiter. In a recent paper published in Nature, the St Andrew researchers describe JWST observations of WD 1856 b, a Jupiter-sized exoplanet much warmer than would be expected for orbiting a dead white dwarf star.
Webb Observes WD 1856 b
A collaboration between NASA, the European Space Agency, and the Canadian Space Agency, the JWST has provided an unprecedented view of the distant edges of the universe, revealing many unexpected finds. Among these surprises was WD 1856 b, whose mass, temperature, and atmosphere readings reveal a surprisingly intact planet after the death of its star.
Our own Sun is projected to exhaust its supply of hydrogen in roughly five billion years, after which it will expand into a red giant star about 100 times larger than it is today, before shedding mass in its final transformation into a white dwarf star.
In the distant future, the Sun’s transformations will likely someday obliterate Mercury, Venus, and even Earth, yet scientists have remained uncertain about how more distant planets will fare. Only by observing real-world examples of planets orbiting dead stars can scientists gather more data on how these scenarios play out for the remaining planets, as with JWST’s observations of WD 1856 b.
A Strange System
Discovered in 2020 by the TESS survey and the Spitzer space telescope, WD 1856 b orbits the white dwarf star WD 1856+534 at a distance of around 80 light-years from Earth.
“The planet is quite the oddball. It’s 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,” said lead author Dr. Ryan MacDonald from the University of St Andrews.
Perhaps the most confounding element of this system is how close the exoplanet is to its host star. At a distance of 50 times closer than the Earth is to the Sun, the planet is at a distance at which the star’s red giant phase should have destroyed it. How the planet managed to escape the destruction while ultimately ending up so close to its star intrigued the St. Andrews team.
James Webb Space Telescope Data
As WD 1856 b performed a grazing transit, where just its top edge passed in front of the host star, JWST observations allowed the researchers to crucially measure mass and temperature data, allowing them to estimate its mass at between four and eleven times that of Jupiter.
“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,” MacDonald said, adding that “it’s like using a time machine to peer into the distant future of our Solar System.”
Infrared light emitted by the planet’s own heat showed a surprising temperature of 126°C, which is 240°C hotter than it would be from the white dwarf’s heat alone.
JWST Tells The Future
As the team worked on the problem, the temperature mystery proved to be the answer to the distance issue.
“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,” said Dr. Christopher O’Connor of Northwestern University. “The other is that the 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 outer companion stars could have influenced WD 1856 b’s orbit.”
Since no present source of energy should be capable of generating this much heat on the exoplanet, the researchers suggest that it represents heat left over from being engulfed by the red giant or possibly through an inward migration. Cooling models the team analyzed indicated that the planet likely first captured heat about 3 to 3.5 billion years ago, then cooled to its present temperature and migrated closer to its host star.
“This is just the beginning of our exploration of planets orbiting dead stars with Webb, and the search for further planets orbiting white dwarfs is ongoing,” Dr. MacDonald concluded. “Our results show that stellar death is not the end – some planets experience a vibrant and lively future after the death of their star.”
The paper, “Aerosol and Hydrocarbons in the Atmosphere of a White Dwarf Planet,” appeared in Nature on July 1, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.