A new study published in the peer-reviewed Astrophysical Journal presents evidence that approximately 100 billion "alien planets" — that is, astronomical objects determined to be orbiting a star — reside in the Milky Way, the galactic home of planet Earth. The Caltech astrophysicists who authored the study say their estimate is "conservative"; there could very well be 200 billion alien planets, many of them circling their stars' "temperate zone," a distance far enough from the star's heat (but not too far) for liquid water to exist naturally, like it does on Earth. One of the study's authors thinks the discovery will help "unlock" the mysterious process by which planets, and planetary systems, take shape:
"I usually try not to call things 'Rosetta stones,' but this is as close to a Rosetta stone as anything I've seen," said co-author John Johnson, also of Caltech. "It's like unlocking a language that we're trying to understand — the language of planet formation."
The study produced a number large enough to trigger a kind of existential anxiety, too:
"It's a staggering number, if you think about it," lead author Jonathan Swift, of Caltech in Pasadena, said in a statement. "Basically there's one of these planets per star."