Embracing uncertainty

Other uncertainties haunt the detection. We don’t know how life began on Earth, so we can’t know if conditions on K2-18b — even if they’d be hospitable for earthlings — could have got life started in the first place. And even if life did evolve there, who’s to say that it’d produce DMS — and if it does produce DMS, why haven’t scientists spotted other biosignature gases?

Still, despite its many, many caveats, most researchers we spoke with agree that there’s reason to celebrate this new study of K2-18b. “It's really an achievement. Thirty years ago, we didn't even know that there are exoplanets,” says Hänni.

Peter Vickers, a philosopher of science at Durham University who’s studied life detection claims, was initially skeptical. “But then the more I looked at it, the more I thought that it actually is quite significant and shouldn't be underplayed either,” he says.

For Madhusudhan’s part, he doesn’t think caution and excitement are mutually exclusive. Even a sliver of evidence for alien life is a “transformational achievement” he says, but there’s a big step from there to a true life detection claim. “We need to recognize both: the achievement and the caution.”

If we do ever find life beyond our solar system, it won’t happen all at once. We’ll slide slowly into certainty, pushed along by findings like this one—hints that there’s something more to discover if only we’d look closer. And this result is, without a doubt, an invitation to look closer at K2-18b. If we find life there, on one of the first potentially habitable planets we’ve inspected closely, says Vickers, we’ll have to assume life is common everywhere; if life is rare, the odds of just stumbling upon the right planet are astronomically low.