Alien Atlantis? Extraterrestrial Life May Be Hiding in Subsurface Oceans of Distant Planets

A new mosaic made from images taken by NASA's Galileo spacecraft in the late 1990's is shown of the surface of Jupiter's icy moon, Europa, as it looms large in this newly-reprocessed, higher resolution color view in this handout provided by NASA November 24, 2014. Reuters

It sounds like something out of the brain of George Lucas: If there is lots of life in the universe, some of that life must have built civilizations, and some of those civilizations must have built empires. Instead, that's the question that got stuck in the mind of Enrico Fermi, a Nobel Prize–winning Italian physicist from the first half of the 20th century who specialized in neutrons and built the first nuclear fission plant on a squash court in Chicago.

But he looked around and didn't see any alien life anywhere, not even a stray militant Wookiee. So he wondered, where is it? And with that, Fermi's Paradox was born. It has obsessed astrobiologists ever since—but now, one scientist thinks he can explain the discrepancy away: the universe seems lonely because the most likely places to find life are hidden away in hard-to-reach subsurface oceans. "I'm not proposing that this is the one and only solution," Alan Stern told Newsweek. "But I think that this one has been overlooked in the past."

Enceladus jets
Enceladus's water vapor jets, emitted from the southern polar region. Image courtesy of NASA/JPL-Caltech and Space Science Institute

Stern is a planetary scientist at the Southwest Research Institute and led the New Horizons mission that flew past Pluto in 2015 and is now headed to rendezvous with a tiny icy rock in the Kuiper Belt that rings our solar system. At a conference last week held by the American Astronomical Society's Division for Planetary Sciences, he gave a talk offering his potential solution to Fermi's Paradox.

His theory caught the eyes of tabloid writers, which doesn't surprise Stern. "This is not my first rodeo." But it's also intrigued his colleagues, including those who specialize in these questions. "They were kind of smacking their foreheads, [saying] 'No, we've never seen this idea.'"

Alan Stern holding a bumper sticker referencing his work with the New Horizons mission. Win McNamee/Getty Images

There's a good reason for that: We've only recently begun to realize just how many ocean worlds there are, even in our own neighborhood. Most of these are moons like Jupiter's Europa and Saturn's Enceladus, which scientists have only begun to study in earnest over the past few decades. Before we started doing so, we had no idea subsurface oceans were so common. "We probably have north of 10 maybe even 20 ocean worlds," Stern says. "Only one of them, Earth, wears its oceans on the outside."

He's quick to emphasize that we don't have any evidence to date for extraterrestrial life in any of these oceans—we just know that they're the coziest-seeming options we've spotted so far. He won't even hazard a guess of which is our best bet. "It would be hard to predict whether one or another one is really in the sweet spot," he said.

NASA's Europa Clipper mission, scheduled to launch sometime in the 2020s, will explore Europa, a moon of Jupiter. NASA/JPL-Caltech

Instead, he's pleased by NASA's continuing interest in sending missions to look more closely at these worlds, like the Europa Clipper mission due to launch in the 2020s. Then we can look to actually sample oceans based on those results.

Because the thing about subsurface ocean worlds, Stern says, is that any life in them is probably not going to come to us—we'll need to go to them if we want to meet them. That's because those oceans are sheltered under thick sheets of ice (or perhaps, on worlds outside our own solar system, of rock as well), which likely makes it difficult to send signals in and out.

And Stern doesn't think ocean-dwelling organisms are very likely to develop spaceflight. Think about dolphins, he says, then consider how much our spacecraft designs are driven by the need to bring as little stuff as possible. Bringing a piece of home with you is harder when home is an ocean than when it's air.

The asteroid Ceres, currently being explored by the spacecraft Dawn, may contain an ocean deep underground. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Moreover, he's not convinced ocean-based life would quite grasp the idea of a universe full of stars and planets, each another unique world to explore. "Once they're on the surface, it's not clear that they would understand the points of light, the stars, and that they'd be able to spend enough time on the surface to develop astronomy," he said.

And they may make precisely the same assumption we did before we started discovering these hidden oceans: That any other intelligent life would be in a world like theirs, tucked beneath an ice sheet and hard to reach. That doesn't make it impossible, just less likely, Stern adds. "It's simply a series of disadvantages to communication."

Stern is giving another presentation on the connection between Fermi's paradox and ocean worlds at next month's Habitable Worlds conference and is working with the journal Astrobiology to publish a paper on the topic as well.