Study Uses Webb Telescope to Probe Future of Solar System Through White-Dwarf Planet
Astronomers observed a Jupiter-sized planet orbiting a white dwarf to infer how planets may survive and migrate after their host star dies, offering clues about the long-term fate of Earth and the outer solar system.
Astronomers from the University of St Andrews have used the James Webb Space Telescope to observe the transit of a Jupiter-sized exoplanet, WD 1856 b, across a white dwarf star about 80 light-years from Earth. The observations allowed the team to measure the planet’s mass, temperature and atmospheric composition, revealing that it is significantly warmer than expected.
The researchers note that the Sun will exhaust its core hydrogen in roughly five billion years, expand into a red giant, and later shed its outer layers to become a white dwarf. According to the study published in Nature, Mercury, Venus and possibly Earth would be engulfed during the red-giant phase, while the ultimate fate of the outer planets remains uncertain.
Lead author Ryan MacDonald explained that WD 1856 b is about the size of Jupiter but orbits a white dwarf only Earth-sized, at a distance 50 times closer than Earth’s orbit around the Sun. He said the planet’s current close orbit could not have existed during the star’s red-giant stage, implying it migrated inward after the star became a white dwarf.
Co-author Christopher O'Connor suggested two possible migration pathways: survival inside the star’s envelope during its death, or gravitational interactions with companion stars in the system’s triple-star configuration. The planet’s measured temperature of roughly 400 K exceeds the heating expected from the white dwarf alone, indicating residual heat from a past heating event.
By modeling the cooling of such sub-stellar objects and combining the Webb data, the team inferred that the heating likely occurred between three and 5.5 billion years after the star’s transition to a white dwarf, supporting a scenario in which the planet moved inward over time and has been cooling since.
The findings demonstrate that planets can persist and undergo dynamic evolution after stellar death, providing a proxy for predicting the distant future of our own solar system.
