LAST WEEK, NASA announced its scientists had found “surprising activity” on Jupiter’s moon Europa. And, just like you’d expect, the space-dork corner of the Internet whipped itself into a frenzy. Because that kind of vague statement can only mean they found aliens, right? Well, not really. But some people are still convinced, even after NASA tried to walk back its blatant nerd-baiting by tweeting that it was definitely not aliens.
We’re here to set the record straight. While NASA didn’t find anything gangly, gray, and bug-eyed on Europa this time, what they did discover is still important. Using the Hubble Space Telescope, scientists caught sight of water plumes bursting out from Europa’s icy surface. If any Europeans are lurking beneath the moon’s surface, they just got a whole lot easier to reach.
The excitement over “activity” on Europa makes sense. In this solar system, having any kind of liquid ocean makes you a member of a pretty exclusive club. As far as we know, the only ocean worlds we’ve got are Earth (duh), Jupiter’s largest moon Ganymede, Saturn’s moons Titan and Encedalus, and Europa. Those moons are where scientists think they’re most likely to find extraterrestrial life in our solar system, if there’s any to find. Europa doesn’t have liquid on its surface like Earth or Titan, but beneath its icy crust is a sizable, H2O ocean situation happening. And we mean big—it covers the whole moon. So as an incubator for life, it’s looking a lot better than Titan’s super-chilled methane lakes.
As a study subject though, Europa’s oceans (and their potential plumes) are tricky. The moon is hundreds of millions of miles away. This study adds independent confirmation of a previous NASA investigation that suggested the existence of the plumes in 2012. Last time, it was Hubble’s imaging spectrograph showing signs of oceanic ingredients in Europa’s atmosphere. For this study, Hubble was looking for geysers silhouetted against the light of Jupiter instead—a technique they adapted from the way scientists study exoplanets’ atmospheres when they pass in front of their stars. But NASA is quick to say that they’re really stretching Hubble to its limits here, so there’s a sizable margin for error.
And the plumes aren’t only difficult to locate because they’re far away. Scientists have known about plumes rocketing out of Saturn’s moon Encedalus for a while now because their activity, which creates ridges on Encedalus’ surface, is bunched up in one location. But Europa is active and ridgy just about everywhere. “The particular orbit of Europa around Jupiter causes tidal forces to essentially knead the moon,” says Adrian Lenardic, a planetary geophysicist at Rice University. The tidal tug of Jupiter’s massive gravity creates those ridges and the frictional heating that could keep Europa’s ocean liquid even so far from a solar energy source—all of which could lead to plumes, but also makes them difficult to spot.
So catching sight of the plumes is no small achievement. And if they’re real, they could make the task of studying Europa’s water a bit more manageable. “We may be able to explore that ocean for organic chemicals, or even signs of life, without having to drill through miles of ice,” says William Sparks, an astronomer with the Space Telescope Science Institute, at a press conference. It would be difficult—and highly expensive—to generate enough power to haul heavy-duty drilling equipment all the way out there. But with geysers intermittently spurting samples of the ocean skyward, you could study the contents of the ocean by just flying through the plumes.
The most exciting outcome of that sample would be finding organic material, but this is a big discovery either way. “Life as we know it and depends on liquid water,” says Lenardic. “Knowing that liquid water can exist at that distance from our star changes what it means to think about places that could support life.” This discovery shifts scientists’ understanding of bodies that can be considered habitable zones—in our solar system and in others. Even if these plumes aren’t home to any Europeans, scientists now have plenty more places to look for signs of life.