Astronomers have developed a replacement technique to look for exoplanets – by trying to find their crushed up bones within the atmospheres of white dwarfs. And it’s working.
The look for planets outside the system, referred to as exoplanets, has one significant limitation: we will only find exoplanets that exist immediately. But our universe has been hanging around for over 13 billion years, and lots of generations of planetary systems have come and gone therein vast expanse of time.
Unfortunately, when stars die they typically take their planets with them. Especially the foremost massive stars, which die as supernova – those deaths usually obliterate any orbiting planet completely. But even when less massive stars just like the sun die, it’s generally bad news for his or her planets.
But as a replacement research paper has acknowledged, that doesn’t remove all evidence of the planetary system off the galactic map. If any planets (or remnant cores of planets) survive, they will occasionally gravitationally scatter off of every other. This doesn’t usually happen in stable systems, but within the death throes of a star anything is feasible (gravitationally speaking).
Some of those scattered objects can head inwards to the white dwarf star, the leftover core of the parent star. That white dwarf star is formed of just about completely pure carbon and oxygen, surrounded by a dense but thin shell of hydrogen and helium. Naturally, any object passing too close will get torn to shreds by the acute gravity of the white dwarf star, with the debris making its paths to the surface to combine and mingle with the hydrogen and helium.
Once there, any elements within the destroyed object, like lithium and calcium, can release their own light, giving a spectral fingerprint that astronomers can potentially spot. Most white dwarfs are too hot, though, which light outshines any contamination. But the recent Gaia mission was ready to map dozens of old, cool white dwarfs, and astronomers have detected the distinct signature of crushed up planets in their atmospheres.
The astronomers found that the abundance of enriched elements matches what we all know from our own system, indicating that planetary systems like ours are within the universe for a really very while.