Astronomers analyzing old archival data from the Hubble Space Telescope have uncovered unusual chemical signatures around the white dwarf star HS 0209+0832, revealing what may be the first known “phoenix planet” formed from the debris of a dead star rather than its original birth.
A decades-old astronomy mystery has finally broken open. Archival observations collected by the Hubble Space Telescope in 1999 contained roughly 100 chemical features that researchers could not identify at the time. Jamie Williams, a doctoral candidate at the University of Warwick in the United Kingdom and lead author of the study, revisited those records armed with updated atomic data and discovered a surprising match.
The research team combined the 1999 Hubble Space Telescope spectrum—which was obtained using the STIS instrument in the far ultraviolet on January 10, 1999, utilizing the MAMA detector and the E140M grating across 1,150 to 1,710 angstroms—with a 2002 spectrum from the Far Ultraviolet Spectroscopic Explorer (FUSE) mission and three exposures taken in July 2000 with UVES. The study was published on 5 October 2026 in Nature Astronomy (DOI: 10.1038/s41550-026-02983-7).
Niobium Clues and the Star HS 0209+0832
When NASA’s Hubble Space Telescope first observed the white dwarf HS 0209+0832, the heavy element signature went unrecognized.
Boris Gänsicke, an astronomer at the University of Warwick, noted that the amount of niobium found in the system was unusual. Study co-author Nicholas Stone, an astronomer at the University of Wisconsin-Madison, explained that this pattern of elements is a telltale sign of the ‘s-process,’ a nuclear reaction that builds heavy elements inside dying stars during their bloated red giant phase.
The star features a surface temperature of about 35,800 kelvin (or roughly 36,329 kelvin based on initial Pan-STARRS photometry and Gaia parallax fits for zero reddening, alongside log g values near 7.918) and a hydrogen atmosphere with roughly 1 percent helium. By the team’s estimate, it has been a white dwarf for about 5 million years. According to the published study in Nature Astronomy, the unusual chemical patterns also include high abundances of zinc and copper, alongside carbon, aluminum, silicon, calcium, titanium, nickel, and iron.
To form a disc of material necessary to birth a planet, HS 0209+0832 likely required a companion star that pulled the ejected material back into orbit, rather than letting it escape, such as a close, low-mass companion that ended up inside the giant star’s envelope.
“What’s remarkable about the planet around HS 0209+0832 is that this isn’t a planet from somewhere else, or a survivor from the system’s birth, it looks like it was built from the very material its own star cast off as it died.”
Boris Gänsicke, Department of Physics, University of Warwick
TESS Observations and Candidate Properties
NASA’s TESS (Transiting Exoplanet Survey Satellite) monitored the white dwarf for four months in observations spanning 2021 and 2023, capturing recurring changes in brightness. Those periodic variations indicate that the system exhibits low-amplitude optical variability with a period of 4.399 ± 0.026 days.
The candidate world circles at a distance of about 3.7 million miles (6 million kilometers) from the white dwarf, placing it much closer than Mercury orbits the Sun (at roughly 4% the distance between Earth and the sun). Analysts estimate the body is a gas giant slightly more massive than Jupiter. Because the stellar remnant remains intensely hot, its extreme ultraviolet radiation strips the planet’s outer atmosphere away, causing a portion of the material to fall back onto the white dwarf.
Implications for the Solar System and Beyond
While a small number of potential second-generation planets have previously been identified orbiting pulsars—a rare type of neutron star and another type of stellar remnant—white dwarfs are much more common, and over 95% of stars in the Milky Way will evolve to become a white dwarf, including our Sun.
Williams added that there is still a lot of work to do to understand how second-generation planets form, how common or rare they are, and how they evolve in orbit around a dead star, with plans to use Hubble and other facilities such as the James Webb Space Telescope to explore these questions and build up substantial data and statistics over the next several years.
T. Williams, B. T. Gänsicke, N. C. Stone, D. Koester, B. D. R. Davies, C. Tong, D. J. Wilson, S. Sahu, A. Swan, T. G. Beatty, S. H. Ramírez, T. Cunningham, and K. S. Long.
