WOODS HOLE, Mass. – The blue water of Buzzards Bay glittered as boats bobbed on the gently undulating surface and gulls swooped among their sails. The seaside air at the Woods Hole Oceanographic Institution was thick with the sweet smell of grass and the tang of saltwater. This was late summer on Cape Cod – our ocean world at its most inviting.
But inside a bay-view conference center, 80 scientists were conjuring up very different ocean worlds: The ice-covered moon Europa, whose watery interior is kept liquid by the gravitational pull of Jupiter. Enceladus, whose south pole emits geyser-like sprays of water vapor, gas and ice; as it orbits Saturn, the tiny moon leaves a glowing trail of particles in its wake.
And then there were the dark, seething systems at the bottoms of our own seas, where the Earth’s crust cracks open, spewing rock, gas and heat – a world as alien to humans as any in outer space.
These ocean worlds are forbidding, hostile, sunless and remote – but many scientists believe they also hold the key to life. Some 4 billion years ago, one hypothesis goes, the chaotic chemistry at the ocean floor provided the fuel for Earth’s first organisms. If life arose elsewhere in our solar system, it probably started under similar circumstances. The only way to know for sure is to go look for it.
That’s why all these scientists were sitting indoors on a glorious August day, their faces lit by the glow of a slide projector rather than the morning sun. In a rare union of two very different scientific communities, the Ocean Worlds meeting convened oceanographers and space explorers with the ambitious goal of guiding the search for life beneath alien seas.
The man responsible for the conference at Woods Hole is geologist Chris German. Last fall he attended a National Geographic Society planetary sciences meeting to discuss exploration of ocean worlds beyond Earth – and quickly realized he was one of the few scientists there who’d actually been to sea.
“There were all these planetary scientists talking about their favorite ocean worlds, Europa or Enceladus or whichever,” he recalled. But their conversation wasn’t grounded in knowledge of how life underwater actually works. “I realized, maybe it would make sense to have some oceanographers here.”
Further piquing his interest, the most recent NASA appropriations bill instructed the space agency to establish an “Ocean Worlds Exploration Program.” The mandate meant NASA would be spending more money on the technology needed for finding life in the oceans: remote controlled robots capable of operating under water and ice, sensors that can detect signatures of life from great distances. Those kinds of tools would also be useful for German’s work on Earth.
“There could be a beautiful convergence in breakthroughs in ocean science and space science,” German said. “We just have to get them together in the same room.”
About half the participants were oceanographers, the other half studied space, with a smattering of engineers and computer scientists attending as well.
“Probably no one in this room will get to see the real fruition of this meeting,” German said to kick off the conference. Finding life in a foreign ocean is like building a medieval cathedral, he said. “The grandparents lay the foundation, the grandchildren build the steeple. The people who lay the cornerstones never get to worship inside.”
The foundation of ocean world exploration is understanding deep sea life on Earth. In 1977, hydrothermal vent systems were discovered by the Woods Hole Oceanographic Institution’s submersible Alvin. Before then, it was assumed that living communities needed sunlight to survive. Yet here were scores of strange creatures – bacterial mats, two-foot-long tube worms, eyeless shrimp – apparently thriving in total darkness.
Colleen Cavanaugh, a graduate student working at Woods Hole at the time, came up with an explanation for the deep ocean’s weird life: chemosynthesis. Undersea microbes can harness the energy from chemicals to produce their own food, much as other creatures use photosynthesis to harness the energy of the sun.
There’s only one kind of sunlight, but there are lots of kinds of chemicals on the sea floor that chemosynthetic organisms can live off. In the past four decades, scientists using Alvin and remotely-operated submersibles have explored scores of other deep ocean systems, each completely different from life as we know it – and from one another. Sulfur-eating organisms live around superhot black smokers. Methane-consumers dwell in cold seeps. Scientists estimate that a new species has been found in one of these systems at a rate of roughly two per month over the past 40 years.
“They are out there in the bazillions in our oceans and we still have a very rudimentary understanding of what they are doing,” said Julie Huber, a scientist at the Marine Biological Laboratory.
Strange creatures have been found in other unlikely places. In 2013, a team lead by Montana State University polar microbiologist John Priscu drilled through half a mile of Antarctic ice to a subglacial lake and uncovered thousands of tiny organisms dwelling in total darkness at subzero temperatures. Like their deep-sea counterparts, the Antarctic microbes made their living off minerals dissolved in the water – and hinted at the potential for life beneath extraterrestrial ice.
“You’d be in denial, I think, to believe there isn’t life out there,” Priscu said.
In 1977, the same year that Alvin uncovered the first deep sea life, NASA launched its two Voyager probes on an unprecedented tour of the planets in the outer solar system.
While zipping past Jupiter, Voyager 1 sent back the first detailed images of Europa – and scientists were astonished by what they saw. The moon’s surface was fractured into sections that fit together like the pieces of a jigsaw puzzle. Rather than being pitted by impact craters, like Mars or our moon, its surface was relatively smooth. Europa looked as though it had plate tectonics, like Earth. That meant that Europa’s solid crust was moving about above a liquid interior, like Earth’s.
The Galileo mission in the 1990s confirmed the theory: Europa has the magnetic signature of an interior ocean full of salt water. It’s able to stay liquid so far from the sun because of a phenomenon called tidal heating – Jupiter’s gravity sloshes it around so much that friction keeps the interior warm.
Just one planet beyond, Saturn’s moon Enceladus is practically screaming to be searched for life. In 2005, during a series of close flybys past the moon, NASA’s Cassini orbiter snapped photos of huge plumes of water vapor, carbon dioxide, nitrogen, methane and some organic molecules surging hundreds of meters above the planet’s atmosphere. Last year, scientists reported that the jets are coming from a vast, watery reservoir in the moon’s interior; like Europa, Enceladus has a subsurface global ocean sandwiched between an icy crust and a rocky ocean floor. And just like ours, that rocky sea floor is almost certainly volcanically active – what else could be sending geysers of water surging into the sky?
“We’re in the position with Enceladus to go back and sample the moon and start asking whether the ingredients are there to support a habitable environment and to search even for life,” said Carolyn Porco, a planetary scientist at NASA and the head of the Cassini imaging team. “And the best part is, you don’t have you don’t have to dig, you don’t have to scratch, you don’t have to drill, you just have to let the stuff fall on you.”
The dwarf planet Ceres, which sits in the asteroid belt between Mars and Jupiter, harbors a huge amount of water ice, and some of it may be liquid. It seems to have formed a towering ice volcano on the planet’s surface. Jupiter’s giant moon Ganymede is thought to be a club sandwich of oceans layered between rock and ice. Saturn’s moon Titan has an ocean as salty as the Dead Sea, and a surface covered in lakes of liquid methane.
“Hearing some of the details … about these oceans in our solar system is captivating,” said Peter Girguis, a deep sea biologist at Harvard. He left the meeting with “all these little kernels of inspiration” for technologies he wants to develop, like sensors that could send back data on their own – something NASA scientists will need if they ever make it beneath the surface of one of these ocean worlds.
If basic research provides the cornerstones for ocean worlds exploration, then technology is the walls and roof beams. Much of the talk at the Ocean Worlds meeting was about the robots, real and imagined, that are needed to explore the remote and hostile places.
Woods Hole computer scientist Yogesh Girdhar demonstrated a program he’d written that allows robots to recognize and track objects of interest without being told to.
Bill Stone, an aerospace engineer who has built tools to explore beneath Antarctic ice, screened a video of his latest “cryobot.” In a matter of seconds, the torpedo-shaped drill blasted through a thick layer of ice, using superhot water warmed by a laser to melt its path.
“We would be at the bottom of any ice sheet on Earth in under six hours,” Stone said.
At lunch, Geoff Collins, a planetary scientist at Wheaton College who has worked with NASA on Europa research, reached out to shake Stone’s hand.
“That was really cool,” he said. The rest of the table nodded their agreement.
The closest analog on Earth to drilling through the ice of Europe or Enceladus is Priscu’s subglacial lake project, WISSARD, which involved drilling through half a mile of ice in temperatures of minus 50 degrees Celsius. On Europa, NASA would have to drill through 60 miles of ice at temperatures lower than minus 180 degrees, all their instruments would have to fit into an average spacecraft’s payload, and all the research would have to follow planetary protection procedures to ensure that Europa wasn’t contaminated with Earthly life.
“This is what we’re up against,” Priscu said.
He is skeptical that subsurface exploration on Europa could happen in his lifetime. There’s still too much work to be done developing the technology for such a mission; he doesn’t envy the engineers who have to figure it out.
Here’s what the future does hold: In 2022, NASA will launch a spacecraft dubbed the Europa Clipper into a long, looping orbit around Jupiter, allowing the craft to perform multiple flybys of the planet’s icy moon. The clipper will carry magnetic sounding instruments to remotely probe the contents of Europa’s ocean and thermal imaging tools to look for signs of recent eruptions of warmer water. An array of other gadgets will snap images of the moon and search for plumes of ice and gas like those seen on Enceladus – if they exist, their contents might hint at the chemistry of the oceans from which they erupt. From orbit, the clipper will assess whether the moon might host life and the where best places to search for it might be.
On Earth, oceanographers are doing research that will help the Europa scientists figure out what to look for. On Tuesday, the two conference organizers, German of WHOI and Kevin Hand of NASA’s Jet Propulsion Laboratory, leave for a two-month mission in the Arctic, where they’ll be using a remotely-operated sub to explore an underwater volcano hidden beneath several feet of ice.
Hand will be scouring the sea ice – both the surface and the side that abuts the ocean – for chemical traces of the organisms living down below. These biosignatures could point to a way to detect distant living organisms without having to send a submarine out in search of them.
“In my dream of dreams, you could imagine, we find life, we’re able trace it up to the ice-water interface, we’re able to trace it into the ice, and then we’re able to trace it to spectroscopy [light signatures] that we can sense remotely via satellites,” Hand said.
“But I don’t think we’re going to get that.”
Thinking back to 1977, when German was a college student and Hand was only two, “it was a golden age of discovery,” German said. Voyager had just launched, Alvin had just made its first visit to the hydrothermal vents on the ocean floor. All of the discoveries that would set the course of their careers were in the midst of being made.
The subsequent 40 years of ocean research and space exploration wound up converging on a single, unifying principle: where there is water, there is almost certainly life. We’ve found it in the deep ocean, we’ve found it under the ice. We think we can find it in space.
“It feels like that golden age is coming around again,” German said. “The intellectual stars are aligning in a way they haven’t for decades.”
It’s a pretty good time to be building a cathedral.
from Department of Space Colonization