Astronomers reanalyzing 1999 Hubble observations of white dwarf HS 0209+0832 have found evidence of a gas giant planet that formed after the star's red giant phase. The work, published in a paper titled "Discovery of a second-generation planet candidate accreting onto a white dwarf," identifies niobium in the star's atmosphere.
Niobium is heavier than iron and, as co-author Nicholas Stone explains, is synthesized only in the exotic conditions inside dying stars. The planet is roughly Jupiter's size, and the white dwarf appears to be stripping its atmosphere, possibly creating a comet-like tail that feeds material back onto the star.
The planet's composition matches no known rocky material around white dwarfs or any meteorite in our Solar System. Co-author Jamie Williams says the planet is likely to survive, as the white dwarf will eventually cool and maintain a stable temperature, leaving the planet in a habitable zone for millions of years.