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How an underwater volcano could help scientists find extraterrestrial life

NASA's "Subsea" expedition is a prelude to a mission to Saturn's Enceladus or another water-rich moon in the solar system.
by Corey S. Powell /
Image: Enceladus
Enceladus's vast subsurface ocean makes it an intriguing candidate for the search for alien life. To prepare for a possible journey to this water-rich moon, scientists are getting a closer look at hydrothermal vents right here on Earth.NASA / Ames
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The next big thing in the search for alien life is taking place closer to home — not in deep space but in the depths around the Lō`ihi seamount, an underwater volcano 22 miles southeast of the Big Island of Hawaii.

As part of a project called Subsea (Systematic Underwater Biogeochemical Science and Exploration Analog), scientists aboard the Exploration Vehicle Nautilus will deploy two remotely operated vehicles, Hercules and Argus, and treat them as if they were deployed on another world.

The mission is a partnership between NASA and the National Oceanic and Atmospheric Administration, with various academic institutions lending a hand. Its main goal is to gain experience with “telepresence” — using video, audio and other data connections to let researchers feel as if they are directly connected to distant robots — says Darlene Lim, a geobiologist at NASA’s Ames Research Center in Moffett Field, California, and the project’s principal investigator. Telepresence could be vital for any coordinated human-robotic effort to seek out microbes on Mars, for instance.

Life-filled vents

After waiting out Hurricane Lane, which dumped 50 inches of rain on the Big Island, the Subsea team now has plenty to examine at the seamount. The region contains an extensive network of hydrothermal vents, where volcanic activity squirts hot, mineral-rich water up from the seafloor. Such locations are rich oases of biodiversity, ranging from clouds of bacteria to giant clams and tubeworms. Hercules and Argus will measure the water chemistry and study the living systems around the vents.

Over the past decade, planetary scientists have come to recognize that similar vents probably exist on Enceladus, a 313-mile-wide moon of Saturn, and on other water-rich moons in our solar system. That realization immediately raised the question of whether living things could find a home around extraterrestrial hydrothermal vents, too.

“Studying Lō`ihi will provide insight into ocean worlds and let us test our predictions about their habitability,” Lim says. The insights gained from Subsea will guide future missions to explore those nearby worlds and to find out if they really do harbor hidden life.

Ice balls alive on the inside?

The inspiration for Subsea comes in large part from the findings of NASA’s Cassini space probe, which orbited Saturn from 2004 to 2017. The probe showed that, beneath its icy surface, Enceladus has a vast subsurface ocean up to 20 miles deep. Cassini also observed jets of water erupting from Enceladus’s south pole. An analysis of the jets confirmed the suspected presence of hydrothermal vents and revealed that Enceladus’s ocean is laced with organic compounds — not proof of life, but highly encouraging.

Image: Enceladus
Dramatic jets of ice, water vapor and organic compounds spray from the south pole of Saturn's moon Enceladus in this image captured by NASA's Cassini spacecraft in November 2009.NASA / JPL-Caltech/Space Science Institute

Giddy space scientists promptly began drawing up plans for follow-on probes that would take a closer look. The Enceladus Explorer, a proposal in development by DLR (the German Aerospace Center), would melt a few hundred feet into the ice — far short of the ocean but perhaps deep enough to find chemical traces of life or perhaps even frozen microbes. The NASA-sponsored Enceladus Life Signatures and Habitability concept would take a more modest approach, sampling the ocean jets from orbit.

These projects are hanging in limbo, however, in large part because they’re seen as risky. “We have theory about what could be happening at vents on other planets, but it’s completely unconstrained by data,” explains Chris German, a geologist at Woods Hole Oceanographic Institution and Subsea’s lead scientist.

Mission planners need a better understanding of the likely conditions on Enceladus before they can design an effective search for life there. For now, we barely understand the hydrothermal vents on our own planet.

Image: Enceladus
An interior cross-section of the crust of Enceladus, which shows how hydrothermal activity may be causing the plumes of water at the moon's surface.NASA-GSFC / SVS, NASA/JPL-Caltech/Southwest Research Institute

“Eighty percent of them haven’t been explored yet, and we’re trying to extrapolate to the rest of the solar system,” German says. “It’s like we’re working with one arm tied behind our back, and putting an eye patch on. I want to be able to answer, ‘If we’re launching a submarine to Enceladus’s ocean, what instruments should it take with it?’”

The Subsea expedition specifically targeted the Lō`ihi seamount because the temperatures and pressures there are broadly similar to those believed to exist on the seafloor of Enceladus. “It is a really nice fit,” German says. Going there will do a lot to chip away at the uncertainties that caused NASA to pass on a previous mission concept called the Enceladus Life Finder.

So, too, will an upcoming mission to another ocean world: Jupiter’s moon Europa. Like Enceladus, Europa has a warm, potentially habitable ocean beneath its icy surface. Nobody yet knows for sure if it, too, has hydrothermal vents, but we may find out soon: In the mid-2020s, NASA plans to send the Europa Clipper probe to take a closer look. German is helping plan the experiments aboard a follow-up lander, which could reach Europa around 2031.

Image: Europa Lander
This artist's rendering illustrates a conceptual design for a potential future mission to land a robotic probe on the surface of Jupiter's moon Europa.NASA / JPL-Caltech

German’s experience with hydrothermal vents on Earth makes him optimistic about what we’ll learn from these missions. “If the Europa Clipper can show us exactly where the ocean has broken through to the surface, then the very first sample will give us really helpful information about the process that are going on down underneath,” he says.

And when the rocket scientists figure out how to chip through the ice and into the ocean, expeditions like Subsea will offer great guidance about what to do next. “We know that volcanic energy isn’t smeared around everywhere — it’s in little hotspot oases,” German says. “You could develop a search strategy for robots to sniff out chemical signals and head toward the oases. If someone can get me through the ice and into the ocean, I know how to do that.”

Humans and robots, working together

Like German, Lim is excited by the prospect of searching for alien organisms on ocean worlds. But she stresses that in addition to being a test run for a mission to Enceladus or Europa, Subsea is an experiment in human-robot interaction.

Lim expects that future human space expeditions will rely extensively on mechanical helpers regardless of destination, even at less extreme destinations like Mars. In fact, she says, the first astronauts to prospect for life on Mars might not actually be on Mars.

“Human operators might be controlling robots on the surface from a nearby orbit,” such as the tiny Martian moon Phobos, Lim says. Such a mission approach could be cheaper and safer than landing astronauts on the planet — and would minimize the possibility of contaminating Mars with microbes from Earth. A follow-up Subsea mission in 2019 (at a different, soon-to-be announced destination here on Earth) will include a 10-minute communication lag, simulating remote control from a distant location.

These experiments are crucial, Lim says, because no human space explorer has ever made extensive, integrated use of robotic helpers the way the researchers on the Nautilus will be working with the Hercules and Argus remotely operated submersibles. Technology has changed radically since the days when the Apollo astronauts piloted their cumbersome buggies on the moon, and mission designs must change accordingly.

“While we are at sea, we will be exploring the unknown,” Lim says. “This project blends ocean science, planetary science and human exploration. For me, it’s a dream come true.”

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