So the niobium around HS 0209+0832 likely traces material the star ejected as it died. The researchers propose that some of that expelled debris clumped together and eventually built a gas giant planet, while the rest dispersed into space long ago.

Co-author Boris Gaensicke, also at Warwick, admitted the finding caught the team off guard. "When Jamie asked me about niobium in relation to this study, I was truly gobsmacked, as that element had not been reported in any other white dwarf analyzed to date," he said.

Does any other telescope back this up?

Two other missions pile on evidence. NASA's retired FUSE mission, the Far Ultraviolet Spectroscopic Explorer, also shows strong niobium signatures in the same system. And NASA's TESS, the Transiting Exoplanet Survey Satellite, monitored the white dwarf for four months and caught repeating dips and changes in brightness.

Those variations suggest a planet orbiting about 3.7 million miles (6 million kilometers) from the star. That's far closer than Mercury sits to our Sun. The team estimates the candidate is a gas giant roughly Jupiter's size, and it appears to be losing its atmosphere fast.

Here's the mechanism the researchers lay out. The white dwarf formed relatively recently, so it's still extremely hot. That intense energy is likely stripping gas from the planet's outer atmosphere, creating a comet-like tail. Some of that escaping material forms a disk around the star before falling onto its surface, and that could be exactly why Hubble sees niobium when it looks at HS 0209+0832.

Even so, Williams doesn't expect the planet to vanish soon. "If the second-generation planet is there, I think it is likely to survive. Eventually the white dwarf will cool and then maintain a consistent temperature, with the planet in its stable habitable zone for millions of years," he said.

What does this change for planet science?

In short, the timeline. Earth and the other worlds of our solar system are first-generation planets, built from material left over from the Sun's birth. A confirmed second-generation planet would show that planet formation doesn't end when a star dies. It can restart.

"Rather than the white dwarf stage being a kind of epilogue to the story of a star and its planets, this research points to the systems we are familiar with only being the first chapter of a potentially much longer tale, with some new characters showing up. That's a really exciting prospect to pursue," Williams said.

Plenty remains unanswered, and the researchers say so themselves. Nobody knows how second-generation planets form, whether they're common or freakishly rare, or how they evolve while circling a dead star. One system is an anecdote, not a statistics base. Williams plans to keep using Hubble over the next several years to gather enough observations to build meaningful numbers on this class of objects.

Gaensicke offered a fitting coda on how the discovery happened at all: "I think this research is an important example of the fact that scientific discovery is not a straight path. It often needs that magical moment when people discuss big questions on their minds and realize that together they can find unexpected answers."

A 27-year-old dataset, an unfamiliar spectral line, and a conversation. Skeptics should hold the champagne until more systems turn up. But the niobium is real, and nobody has explained it any other way yet.