Nasa’s James Webb Space Telescope solves the mystery of a planet that survived its Sun’s death |
A white dwarf is usually thought of as the quiet remnant left behind after a star has exhausted its fuel and shed much of itself into space. By that stage, any worlds that once orbited nearby are expected to have faced a violent fate. Yet one planetary system roughly 80 light-years from Earth appears to have followed a different path.According to information released by Nasa, observations from the James Webb Space Telescope have provided fresh insight into a gas giant called WD 1856 b, a planet that circles a white dwarf at an extraordinarily close distance. The finding is attracting attention because the planet appears to have survived the turbulent final stages of its star’s evolution. By studying its atmosphere and temperature, astronomers have pieced together a likely explanation for how the world avoided destruction and eventually settled into its present orbit. The work offers a rare glimpse of what could happen to giant planets in ageing planetary systems billions of years from now.
WD 1856 b: A planet orbiting the remains of a dead Sun
WD 1856 b was first identified in 2020 through observations from Nasa’s Transiting Exoplanet Survey Satellite (TESS) and the retired Spitzer Space Telescope. The planet orbits the white dwarf WD 1856+534 once every 34 hours, remaining less than three million kilometres from the stellar remnant.That distance poses an obvious problem. Before becoming a white dwarf, the star expanded into a red giant, a phase during which its outer layers swelled dramatically. Any planet occupying WD 1856 b’s present position would almost certainly have been engulfed.The planet itself is roughly comparable in size to Jupiter, while the white dwarf is only about the size of Earth. This unusual arrangement means the planet blocks more than half of the star’s light whenever it passes in front of it, making the system particularly useful for detailed observations.
How Nasa’s James Webb Space Telescope studied the atmosphere of the planet
The James Webb Space Telescope was used to observe one of these transits in infrared light. By examining subtle differences in the light reaching the telescope, astronomers were able to estimate the planet’s mass and investigate conditions within its atmosphere.The data suggested that WD 1856 b has a mass somewhere between four and eleven times that of Jupiter. Webb also detected signs of atmospheric methane along with evidence for small cloud particles. It marks the first time scientists have identified an atmosphere on a planet known to transit a dead star.As per Nasa, an unexpected detail emerged from the temperature measurements. The planet appears to be around 126 degrees Celsius, considerably warmer than expected if it were heated only by the faint light of its white dwarf host. That excess warmth turned out to be one of the most important pieces of evidence in the investigation.
Why scientists believe WD 1856 b moved closer to its white dwarf
Astronomers examined two possible explanations for the planet’s survival. One possibility involved the world being swallowed by the expanding red giant and somehow enduring conditions inside the star. The alternative suggested that the planet originally orbited much farther away and migrated inward later.The temperature data helped separate those scenarios. By modelling how large planets cool over immense timescales, researchers traced the planet’s thermal history backwards. The results indicated that the heating event responsible for its current warmth likely occurred long after the star had already become a white dwarf.That timing points towards orbital migration rather than survival inside the red giant itself. The white dwarf belongs to a triple-star system, meaning two companion stars are present. Their gravitational influence may have gradually disturbed WD 1856 b’s orbit, pushing it closer and closer to the white dwarf over billions of years.As the planet spiralled inward, intense gravitational interactions would have generated heat within the planet. The warmth detected today appears to be leftover energy from that process, slowly leaking away over time.
What WD 1856 b reveals about the future of the solar system
The discovery reaches beyond a single unusual planet. In around five billion years, the Sun is expected to enter its own red giant phase. Mercury and Venus are likely to disappear, while Earth may also be consumed. After shedding its outer layers, the Sun will eventually become a white dwarf.What happens to the outer planets after that remains uncertain. Worlds such as Jupiter and Saturn could survive, though their future orbits may change dramatically as the solar system evolves.By examining systems like WD 1856+534, astronomers are effectively studying a possible future version of our own neighbourhood. The observations suggest that giant planets can remain intact long after their parent stars die and may continue to migrate through altered planetary systems for billions of years.According to Nasa, additional Webb observations of WD 1856 b have already been carried out to investigate its atmospheric chemistry in greater detail. Those measurements may reveal more about the planet’s history and provide further clues about the long-term fate of planetary systems orbiting stars like the Sun
