Astronomers detect exotic elements in HS 0209+0832’s atmosphere, evidence of a second-generation planet

Astronomers using the Hubble Space Telescope, the Far Ultraviolet Spectroscopic Explorer and the Transiting Exoplanet Survey Satellite detected copper, zinc and niobium in the atmosphere of the white dwarf HS 0209+0832, a dense stellar remnant, evidence of a second-generation planet assembled from the dead star’s own debris now orbiting the remnant, in work reported Oct. 22, 2026 by a team led by Jamie Williams of the University of Warwick.

White dwarfs are the dense remnants of stars like our Sun after they exhaust their nuclear fuel and shed their outer layers, leaving a small, hot core. HS 0209+0832 is unusually hot at 35,000 kelvin, about 63,000 degrees Fahrenheit, well above the Sun’s 5,800-kelvin surface, and the remnant is newly formed. The Hubble Space Telescope first observed the star in 1999 and recorded an unexpected excess of helium in its atmosphere.

Williams noted that HS 0209+0832 is typical in size and mass, about 0.5 times the mass of the Sun and roughly the size of Earth, but unique in its chemical composition. He said that implies other white dwarfs may host similar second-generation planets. The research appeared in Nature Astronomy.

The Transiting Exoplanet Survey Satellite measured brightness changes in HS 0209+0832 that repeat every 4.4 days, a pattern consistent with an orbiting planet creating a day-night phase curve as different faces of the world rotate into view. Researchers read the signal as a close-in gas giant, perhaps like a hot Jupiter, circling about 6 million kilometers from the white dwarf.

The researchers propose that the progenitor star, similar to our Sun, expanded into a red giant and ejected material enriched with zinc, copper and niobium. The white dwarf is now consuming the planet’s atmosphere, which accounts for the rare elements seen in the white dwarf’s atmosphere.

Niobium had never before been detected in the atmosphere of a white dwarf, so HS 0209+0832 is the first known case. White dwarf atmospheres are normally almost pure hydrogen and helium because heavy elements sink inward, meaning heavier traces point to pollution from orbiting material. Niobium is rare on Earth and is used in jewelry, rocket systems and superconductors.

Jamie Williams, the study’s lead author, said, “This white dwarf is unique because it has a lot of traces of copper, zinc, and niobium,” and added that the James Webb Space Telescope could directly detect the planet because its high temperature should make it glow in the infrared.

Juliette Becker, a planetary astronomer at the University of Wisconsin–Madison, said the pollution profile of HS 0209+0832 is unlike anything observed. Becker, who studies unusual planetary formation scenarios, said the chemistry does not match comets or meteorites and indicates a novel formation process for the system.

Becker suggested that second-generation planets around white dwarfs are likely common. She cited the similar worlds already found around pulsars, the remnants of more massive stars.

Zifan Lin, a planetary scientist at Washington University in St. Louis, called the discovery direct evidence for a process that had been speculative. Theoretical predictions of second-generation planets date back more than 15 years, and the study in Nature Astronomy provides the first observed evidence of such a world. Lin emphasized that the finding shifts second-generation planets from a theoretical hypothesis to a confirmed phenomenon.

The discovery suggests that planetary systems can have a second life after their stars die, challenging earlier assumptions about their fate.

Williams also offered an analogy: “A phoenix is reborn from the ashes of its predecessor, and this planet is formed from the ashes of the star,” he said. The phrase captures a world built from the material a star sheds as it dies.