White dwarf HS 0209+083 may host second-generation planet

Popular Science reports that astronomers have detected what could be the first known planet formed from the debris of a dying star. The candidate orbits the white dwarf HS 0209+083, a dead star about 1,200 light-years away.

The study, published in Nature Astronomy, was led by Jamie Williams of the University of Warwick. Williams and colleagues analyzed the white dwarf's atmosphere and found unusually high levels of heavy elements: copper, zinc, and niobium. The niobium content is more than 1,000 times what the sun contains. Such an elemental mix, the researchers argue, is a chemical fingerprint of a second-generation planet — one assembled from material ejected during the star's death, not from the original planetary system.

Data from NASA's Transiting Exoplanet Survey Satellite (TESS) shows a faint brightness signal repeating every 4.4 days. That suggests a gas giant roughly the size of Jupiter in a very close, tidally locked orbit. The planet's proximity to the white dwarf would mean its atmosphere is slowly disintegrating from radiation, with that material eventually falling onto the star.

Co-author Nicholas Stone, a University of Wisconsin-Madison astronomer, said the chemical signature is not one that a normal first-generation planet should carry. "It's a chemical signature no ordinary, 'first-generation' planet should carry, which told us that this new planet was something different," he told Popular Science.

The scenario requires a special setup. A single dying star typically ejects its mass symmetrically, scattering material into space. To form a new planet, HS 0209+083 probably needed a companion star to pull that material back into orbit. If confirmed, the discovery gives astronomers a new way to search for other second-generation worlds around dead stars.

Co-author Boris Gänsicke, an astrophysicist at the University of Warwick, described it as a system that "has given birth to a new world using the foundations of the old one."

The study is peer-reviewed, but the planet remains a candidate. The TESS signal could have other explanations, and the planetary interpretation relies on matching the chemical and brightness data. Still, the finding opens a new line of inquiry for planet formation in the aftermath of stellar death.

• Boris Gänsicke
• HS 0209+083
• Jamie Williams
• Nature Astronomy
• Nicholas Stone
• second-generation planet
• TESS
• white dwarf