Astronomers using the James Webb Space Telescope have probed WD 1856 b, a Jupiter-size gas giant orbiting a white dwarf just 75 light-years from Earth. Discovered by TESS in 2020, the planet circles its stellar remnant at only 0.02 AU — a position that defies standard models of stellar death. When Sun-like stars expand into red giants, they should engulf inner planets and push survivors outward as they shed mass. WD 1856 b instead migrated inward.

JWST captured an eight-minute transit on April 27, 2023. Because the white dwarf is seven times smaller than the planet, the transit grazes the star's edge, requiring new mathematical tools to extract atmospheric data. The spectrum reveals aerosol hazes and methane at 7 percent — far above Jupiter's 0.3 percent. More strikingly, the planet glows at 400 Kelvin, emitting 25 times more energy than it receives from its cooling host.

Cooling models trace this excess heat to a reheating event 3 to 5.5 billion years after the red giant phase ended 5.4 billion years ago. That timing rules out survival inside a common stellar envelope and points to high-eccentricity migration driven by gravitational kicks from two distant stellar companions. The planet spiraled inward through repeated plunges, generating tidal friction that heated its interior.

A major caveat remains: the methane-rich atmosphere may invalidate standard cooling models, which assume Jupiter-like composition. The team has already collected additional JWST data to refine the picture. If WD 1856 b is typical, planetary survivors of stellar death could be common in the solar neighborhood.