If alien life exists in our solar system, it may look like this

Icebreaker R.V. Kronprins Haakon, off Greenland — Outside, the sinking sun is coloring the autumnal sky a brilliant lavender, a rich hue that lingers over a vast blanket of ice. Here, off the northern coast of Greenland, the Arctic Ocean is masquerading as land, a snowy patchwork of smooth ice floes and abrupt, jagged piles of crystalline debris. Only the subtle shifting of our ship, the Norwegian icebreaker R.V. Kronprins Haakon, betrays the landlocked illusion.

It took longer than expected to get to this icy wonderland from the small coal-mining town of Longyearbyen, the most populated port in Norway’s Svalbard archipelago. Now that we’re here, Chris German isn’t paying much attention to the dramatic seascape. Instead, he’s staring intently at a live feed of the seafloor, and he’s trying on hats. Every 10 minutes or so, he plops a different hat on his head, rotating through haberdashery that includes a faux sealskin ushanka, a woven orange fez, and a beanie from the Woods Hole Oceanographic Institution, where he works.

The costume changes help German pass the time while we wait for the first glimpse of our quarry: a broken patch of seafloor that’s pumping smoky, superheated fluids into the darkness, perhaps helping to power one of the most alien ecosystems on Earth. This elusive zone is called the Aurora hydrothermal vent field. It’s the most northerly vent field yet known, and it’s among the deepest in the world, sitting nearly 2.5 miles below a permanent covering of sea ice.

Exploring the deep sea, like venturing into deep space, is a high-risk endeavor. The abyssal seafloor is an unforgiving place for even the hardiest robots, and this mission has seen its share of mishaps, including a few heart-stopping days when it seemed like the team had lost its main underwater rover to the freezing polar ocean.

But on this violet evening, after hours of drifting over a muddy seafloor, a high-resolution camera towed beneath the ship at last passed directly over a gaping maw in Earth’s crust. Beamed onto screens throughout the ship, the footage revealed an angry black plume erupting from a crater measuring nearly five feet across—an astonishing span for this flavor of undersea smoker.

“That is a big f***ing plume,” German said, his rotating headgear paused on the ear-flapped ushanka. “This is a lot more than we knew was here.”

Later that night, the same camera would fly over the site twice more; and multiple passes over the next week would reveal wildly rugged terrain populating the southern slope of the Aurora seamount. The images revealed that the vent field is covered with extinct chimneys, heaps of extruded minerals, and not just one, but at least three black smokers.

The results offer our best look yet at such an exotic, ice-shrouded ecosystem. Better understanding this remote biosphere could help scientists figure out how creatures move through Earth’s deep oceans, and whether Arctic waters form a pathway for animals moving between the Atlantic and Pacific basins.

“The idea is to really understand this area when it’s still pristine,” says deep-sea ecologist Eva Ramirez-Llodra, the project’s lead scientist from the Norwegian Institution for Water Research. “If climate change gets rid of the ice, this will become a more used route to go to the Pacific, and it could become an open area for potential mining, for fisheries ... it’s good to know what’s there.”

What’s more, the Aurora vents could hold the keys to detecting life-forms in the deep oceans on alien worlds. For now, Aurora is one of the closest Earth-analogs to the seafloor vents that are thought to be erupting on faraway ocean worlds, including the ice-encrusted moons Europa and Enceladus, which are considered among the best places to look for existing extraterrestrials. (Find out more with our interactive atlas of moons.)

“Alien oceans beyond Earth are so compelling in the search for life elsewhere,” says National Geographic Explorer Kevin Hand, an astrobiologist at NASA’s Jet Propulsion Laboratory who took part in the Aurora expedition. “Wherever we’ve looked on planet Earth and found liquid water, we’ve found life.”

Plethora of vents

In general, oceanic hydrothermal vents arise when seawater seeps through cracks in Earth’s crust and mingles with hot rocks beneath the surface; those buried molten rocks heat the saltwater and fuel chemical reactions that erupt in a roiling mass through vents in Earth’s crust. The continual extrusion of mineral-rich, superheated seawater provides the heat and energy needed for some organisms to thrive in these cold, dark depths, including a menagerie of vent-specific gigantic tube worms, foot-long clams, blind shrimp, and extreme microbes.

For a long time, canonical wisdom had suggested that hydrothermal vent activity could only exist at the fastest spreading mid-ocean ridges—places like the East Pacific Rise, where Earth’s tectonic plates are hustling away from one another at speeds of around seven inches a year. At these bursting planetary seams, the brisk spreading of Earth’s crust means that fresh magma is always available to fuel the vents.

Over the years, though, German and his colleagues have found vents populating a variety of ridges, including some that languidly go their separate ways. Our most recent target, the Gakkel Ridge, is a volcanic rift bisecting the Arctic Ocean that is spreading at the stultifying rate of less than half an inch a year.

“Nowhere is precluded from having hydrothermal activity,” German says. “We can dispense with that myth now.”

Scientists first went prospecting for hydrothermal plumes along the Gakkel Ridge in 2001. During that cruise, a layer of murky water detected near the seafloor hinted at vent activity, and a rock-dredge pulled up the remains of an extinct chimney. Both observations could be explained by black smokers, the sort of vents that launch towers of dark, hot plumes into the water.

During a second cruise in 2014, German and his colleagues returned to Aurora aboard the icebreaker Polarstern. They searched for vents by looking for hydrothermal signatures in the water column and, toward the end of the cruise, they dropped a high-resolution camera into the deep. Just two hours before it was time to head home, the team caught their first glimpse of a small chimney, a fleeting photobomb by a smoking vent that slid into the margins of several frames.

But the vent signatures written into the freezing sea suggested that something much more massive must lie below. Buoyed by that discovery, this year’s expedition, known by the acronym HACON, aimed to put the Aurora vent field into context. How extensive is the entire system? What kind of chemistry is involved? Can the vent support a deep-sea ecosystem, and if so, what kinds of organisms live there?

And, for the astrobiologists on board, what insights might the site bring in efforts to detect life on ice-covered ocean worlds across the solar system?

Bad champagne

Answering these questions presented challenges even before the icebreaker left port. The high-resolution camera that proved so vital to the mission, called the Ocean Floor Observation and Bathymetry System, or OFOBS, was initially mis-bundled with gear destined for a different polar expedition. Worse, a deep-diving, remotely operated submersible from Woods Hole called Nereid Under Ice, or NUI, was very nearly lost to the deep.

NUI is a state-of-the-art, $2.5-million submersible roughly the size of a minivan. It can spend half a day underwater before being recharged, can swim more than 25 miles from the ship, and can dive three miles down without imploding, allowing it to work under thick ice cover.

The bright orange submersible has an on-board brain that lets it function human-free, yet it can also be remotely piloted, meaning that scientists watching a live feed from its cameras can tell it to pluck specific animals from the deep-sea floor, dunk collecting tubes into particular sediments, and dip specially designed probes straight into the effervescent, sulfuric fluid erupting from a hydrothermal vent. Geochemist Eoghan Reeves of the University of Bergen, who once (accidentally) took a swig of the seafloor libation, and says the bubbly mixture resembles bad champagne: “It smells just terrible, and it tastes exactly like it smells.”

But two days after arriving at the Aurora seamount, NUI dove and did not come back up. As the sub neared its target depth, its onboard systems blinked off one by one. Engineers tried to coax it to float back up on its own, triggering a fail-safe mechanism that should have released its dive weights and restored buoyancy. Instead of rising, NUI stopped moving, its depth reading becoming a foreboding line that marched across a screen in the ship’s control room.

“The likelihood that it’s resting on the bottom is pretty high—in which case, game over,” Andy Bowen, director of WHOI’s National Deep Submergence Facility, finally said. Without NUI, even catching a glimpse of the vent meant relying only on OFOBS, the high-resolution camera. But that camera isn’t steerable and could merely be towed along behind the ship, which meant that successfully spotting the undersea plume depended on cooperatively drifting ice or floes thin enough to break.

“We knew coming out there would be difficult, that we would face challenges, but this is beyond any of our expectations,” said Benedicte Ferre, a physical oceanographer at the University of Tromsø.

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Mordor of the deep

Fortunately, NUI resurfaced after three days; the fail-safe had simply taken a little longer to work than anticipated. Even better, while NUI was being fixed up, the icy patchwork covering Aurora allowed the ship’s captain to fly the OFOBS camera directly over the Aurora vent site.

That evening, scientists were clustered around TV screens throughout the ship, anxiously watching the seafloor drift by under the inky twilight. Soon, a layer of nearly black gravel crept into view, carpeting the sticky beige mud that had slid by for hours. Brilliant orange and yellow patches appeared, and the camera began climbing, moving up a stunningly steep, craggy wall.

The 50-foot-tall formation came out of nowhere—pinnacles of volcanic material vomited from beneath the seafloor. The pumice-like sediments grew darker and darker, and then, for a moment, a violently churning cloud tickled the corner of the image, followed by the curving jaw of a giant, toothed crater. As the ship drifted, the cloud expanded into a massive black plume that engulfed the camera and continued billowing upward for nearly half a mile. This smoker was clearly a behemoth that dwarfed the average chimney. Later tows would reveal even more black smokers on the seafloor.

“Satanic, like the satanic mills of the Industrial Revolution. Mordor,” German said of the giant vent. “We knew there had to be more than what we saw in 2014.”

Based on the extensive heaps of sulfides and extinct chimneys, the Aurora vents have almost certainly been active for millennia, perhaps seeding the Arctic seafloor with heat and minerals since before humans first arrived in the Americas.

But exactly how long the site has been erupting is still an open question, as are many of the other mysteries the team set out to solve. Without many samples from the site’s life-forms, for instance, the team doesn’t have the genetic material needed to easily answer several of their pressing questions about how creatures move between ocean basins.

Silica skeletons

More puzzling, at least in some ways, is that the Aurora ecosystem appears to be unusually sparse, at least in the images collected from this cruise. Here, there are no obvious tubeworm meadows, sharp beds of mussels, or colorful carpets of anemones. Even microbial mats, although visible in some areas, are conspicuously lean. This vent, it seems, is the realm of small snails and scavenging, shrimp-like crustaceans called amphipods.

“It’s nothing compared to vents in other oceans, where you have huge amounts of animals,” says Ramirez-Llodra, who adds that “we just have a few images. And they are great images, but we haven’t really surveyed the area in detail.”

Ana Hilário, an ecologist from Portugal’s Universidade de Aveiro, was particularly stunned by the absence of Sclerolinum, a type of polychaete worm that’s abundant elsewhere in the deep sea. She and Hans Tore Rapp, a taxonomist from the University of Bergen, suspect that the Arctic seafloor might be sparsely populated primarily because the north polar ocean is still geologically young—roughly 60 million years old—and deep-sea fauna may not have had enough time to find their way into these waters and adapt to the extreme conditions.

The only organisms that really appear to thrive in the area are two types of glass sponges, creatures named for their filigreed, glassy skeletons. Sometimes measuring more than three feet across, and with lifespans predicted to span centuries, these glass sponges are occasionally said to be barely alive. Perhaps less than five percent of their biomass is organic, and the rest is silica, the same stuff that makes sand and glass. Fortunately, NUI dove to the seafloor after being fixed up and collected some glass sponges from a spot near the vent.

Rapp suspects that these sponges can thrive in a potentially nutrient-starved, carbon-choked ecosystem precisely because they don’t require much particulate organic carbon. Instead, they’ve adapted to survive on low concentrations of dissolved organic matter and make their skeletons out of more readily accessible building blocks.

“Silica in the deep is always easily available,” Rapp says. “There’s almost no cost to build skeleton.”

The observations raise some tantalizing possibilities for what might be lurking in the seas beyond Earth, where sunlight is scarce and the only reliable form of energy might be chemically generated by the heaving innards of an ice-crusted moon.

Kevin Hand says that a lot of the work he’s doing at NASA involves figuring out what kinds of biosignatures to look for in the icy sheaths cocooning alien seas. That’s one of the reasons he’s studying Aurora’s ice, to figure out if it holds signs of the life-supporting vents that scientists can learn to recognize—on Earth and, perhaps, on other worlds.

“Using the ice as a window to the ocean below,” he says, “this is relevant to how we actually learn about these oceans that are beyond Earth.”