Astronomers scrutinize exoplanet that survived the death of its star

Astronomers scrutinize exoplanet that survived the death of its star

An international team of astronomers has used the James Webb Space Telescope to analyze a Jupiter-sized exoplanet that continued to exist billions of years after its sun-like host star died. The planet, named WD 1856 b, is located 81 light-years from Earth in the constellation Draco.

The discovery provides a window into the potential future of the solar system. In approximately 5 billion years, the sun is expected to exhaust its hydrogen fuel and expand into a red giant, becoming about 200 times its current size. This phase will definitely destroy Mercury and Venus, and may engulf Earth, before the sun expels its outer layers to leave behind a compact stellar remnant called a white dwarf.

WD 1856 b orbits a white dwarf named WD 1856+534. This white dwarf formed from a star that was up to twice the sun's mass and died about 5 billion years ago. While the white dwarf is only slightly larger than Earth, it is far more massive than the planet, though the planet remains about 500 times bigger than the star in volume.

The Mystery of the Tight Orbit

The exoplanet orbits its dead star every 34 hours, or 1.4 days, at a distance less than 3 million km. This is 50 times closer to the white dwarf than Earth is to the sun. Because the planet would have been destroyed if it had been at that distance during the star's red giant phase, researchers are investigating how it arrived there.

Two competing theories exist for the planet's current position, according to astrophysicist Christopher O'Connor of Northwestern University in Illinois.

• The planet was swallowed by the host star during its red giant expansion but survived just outside the stellar core.
• The planet originally orbited far enough to avoid engulfment but was later pushed inward by the gravitational influence of other objects.

WD 1856 b exists in a triple star system. The white dwarf is accompanied by two red dwarf stars, each roughly 30% of the sun's mass, which may have influenced the planet's orbital migration.

Thermal and Chemical Clues

To determine which theory is more likely, the team used the James Webb Space Telescope to measure the planet's temperature and atmospheric composition. They found the planet is unexpectedly warm, with an atmospheric temperature of about 260 degrees Fahrenheit (127 degrees Celsius).

Researchers concluded this heat is residual energy. Because there is no current energy source to generate such warmth, the heating likely occurred between 3 and 5.5 billion years after the star became a white dwarf. This suggests the planet remained in a wide, safe orbit during the red giant phase and only migrated inward later.

"As the planet moved inwards, its interactions with the strong gravity of the white dwarf will have caused it to warm up considerably, and it has been cooling ever since,"

Christopher O'Connor, astrophysicist, via Reuters

The telescope also detected the first atmosphere ever seen on a planet transiting a dead star. The gas giant is composed mostly of hydrogen and helium, similar to Jupiter, but it contains an unusually high amount of methane and small cloud particles.

Implications for Earth and Jupiter

The findings suggest that gas giants in our own solar system may persist after the sun's death. However, O'Connor noted that the dynamics of WD 1856 b differ from what our planets will experience. As the sun becomes a white dwarf, it will lose about half of its mass, which is expected to cause surviving planets to drift away until they reach about double their current orbital distances.

The fate of Earth remains uncertain. We cannot predict Earth's future orbit well enough to know whether it will be inside or outside the 'danger zone', O'Connor said.

The original existence of WD 1856 b was disclosed in 2020 after being detected by the Spitzer Space Telescope and the Transiting Exoplanet Survey Satellite (TESS). The current findings were published 1 July 2026 in the journal Nature.

Astronomers have recently observed four additional transits of WD 1856 b with the James Webb Space Telescope to further examine its atmospheric chemistry. Results from those observations are pending.