Discovery of a second-generation world

Astronomers led by the University of Warwick and the Instituto de Astrofísica de Canarias have detected evidence of an exoplanet formed from the material expelled by its dying host star. Published on 5 October 2026 in Nature Astronomy, the research identifies a gas giant orbiting the white dwarf HS 0209+0832, located between 250 and 270 light-years from Earth in the constellation Cetus. Unlike first-generation planets that coalesce alongside newborn stars, this world formed from the leftovers of a doomed star slightly larger than the Sun. While potential second-generation planets were previously proposed around pulsars, this discovery represents the first example confirmed around a white dwarf.

In myths, a phoenix is born again from its own ashes. In the case of this planet, it is born again from the ashes of its dying host star, and therefore the planetary system is reborn. A second-generation planet is defined as one born after its host star dies -- in this case after it has become a white dwarf.

Atmospheric composition and the s-process

The study resolves an astronomical puzzle dating back to 1999, when the Hubble Space Telescope recorded over 100 unidentified spectral lines in the atmosphere of HS 0209+0832. Under the intense gravitational pull of white dwarfs, heavy elements typically sink rapidly below the surface, leaving atmospheres dominated by hydrogen and helium. While typical polluted white dwarfs exhibit debris from rocky asteroids containing iron and silicon, HS 0209+0832 revealed elevated abundances of zinc, copper, and niobium at concentrations over 1,000 times higher than in the Sun. Spectroscopic analysis coordinated by Boris Gänsicke identified these elements as byproducts of the slow neutron capture process, known as the s-process. This detection marks the first time niobium has been observed in a white dwarf atmosphere.

This elemental pattern is the hallmark signature of the s-process, a nuclear reaction that builds heavy elements inside dying stars during their red giant phase. It is a chemical signature that no normal first-generation planet should possess, which told us that this new planet is something special.

Extreme orbital dynamics and stellar accretion

Observational data from NASA's Transiting Exoplanet Survey Satellite (TESS) revealed a repeating photometric signal with an orbital period of 4.4 days. The companion is a gas giant with a mass comparable to or slightly larger than Jupiter, orbiting at 4% of the distance between Earth and the Sun. Due to its proximity to the host star, the planet is tidally locked, presenting the same face to the white dwarf throughout its orbit. Extreme ultraviolet radiation from the stellar remnant heats the planet's atmosphere, causing volatile and metallic material to evaporate and fall directly onto the stellar surface.

Formation mechanisms and observational history

Researchers hypothesize that the planet coalesced from a secondary protoplanetary disk formed during stellar death. A gravitational interaction or collision between the dying star and another body, such as a low-mass star or a brown dwarf, likely trapped the expelled gas and dust rather than allowing it to disperse into space. The research integrated observations from the Hubble, TESS, and Far Ultraviolet Spectroscopic Explorer (FUSE) telescopes. The team plans to use the James Webb Space Telescope to conduct further spectroscopic analyses and confirm the system's evolutionary history.