This enhanced-color view from NASA’s Galileo spacecraft shows an intricate pattern of linear fractures on the icy surface of Jupiter’s moon Europa. Credit: NASA / JPL-Caltech / SETI Institute
In recent years, a team of scientists has been traveling to Antarctica, drilling into the ice, and deploying aquatic robots to learn about an underwater alien world teeming with life.
“We see these ice algae and anemones that will burrow in where it’s pitch black,” says graduate student Jacob Buffo, who studies planetary science at the Georgia Institute of Technology in Atlanta.
Buffo is part of the Sub-ice Investigation of Marine and Planetary-analog Ecosystems (SIMPLE) project, a NASA-funded venture investigating otherworldly Antarctic spots in order to better understand extraterrestrial ecology. The thriving ecosystems found hundreds or even thousands of meters below the icy surface can help researchers better imagine the possibilities on distant ocean worlds in our solar system. Though often overlooked when speculating about where to find life beyond Earth, the interface between ocean and ice can be a rich and nurturing habitat. With NASA gearing up to design and launch a mission to Jupiter’s frozen moon Europa, studying such extreme environments may provide an important foretaste of the future.
When the SIMPLE team’s robotic explorers drop into the Antarctic ocean, they find a topsy-turvy landscape. The underside of the ice shelf contains rolling hills and craggy canyons—all, of course, upside-down. Hotter and colder currents slowly reshape the topography, making the world below the ice an ever-changing experience. Because of its salinity, the water freezes at different temperatures along the bottom of the shelf, creating a porous fluff.
A view of ARTEMIS under the sea ice near the borehole during the final mission. Credit: Bill Stone
“When you look at the bottom of the ice shelf, you’d expect this solid smooth boundary,” Buffo says. “But when you get down there, you have this slushy crystalline layer—partially liquid and partially solid.”
ARTEMIS creates a 3D sonar point cloud map underneath Big John Crack. Credit: Evan Clark
Interactions between melting freshwater glaciers and the cold salty ocean water stimulates the growth of crystals that sometimes rain upward—“kind of like upside-down snow,” says Buffo—adding to this mushy layer. Nutrients can flow through this permeable snow-like material, creating an unexpectedly ideal place for living creatures.
Near the surface, where light can still filter through the ice, algae blooms and provides food and oxygen for other organisms, such as krill. Fish seek shelter in small open pockets in the ice. And in 2014, scientists discovered a bizarre spindly sea anemone clinging to the slushy bottom. Since most anemones anchor themselves in sand, scientists speculate that the fuzzy layer provides a way for the ice-dwelling species to remain entrenched, similar to tree roots plowing into soil. Exactly what the anemones eat, how they reproduce, and how they survive the frosty temperatures remains unknown at this point.
Edwardsiella andrillae; a new species of sea anemone from Antarctic ice. Credit: Marymegan Daly Frank Rack Robert Zook
While the icy crust of a place like Europa is about ten times thicker than the ice shelves of Antarctica, the terrestrial system provides a near-perfect analog to what we might expect to find on the distant frozen moon. Buffo has also created models using earthly data that extrapolate the possible thickness, composition, and habitability of the Europan underwater ice environment, which he will present next month at the American Geophysical Union conference in San Francisco. Both the simulations and the biodiversity seen in Antarctica bode well for potential alien organisms on frozen ocean worlds in the solar system.
But many questions remain about Europa, such as exactly how salty its ocean is and whether or not its internal chemistry is conducive to life as we know it. NASA is currently planning to build the Europa Clipper mission, a spacecraft expected to conduct multiple flybys of the frozen moon in the 2020s and possibly zip through one of the plumes thought to periodically erupt from its surface. The most recent congressional NASA budget included funding for a lander that could touch down atop the enormous ice sheets.
The SIMPLE project’s fleet of robotic explorers will likely help inform both Europa Clipper and any future missions. One of them, Icefin, is a small tethered probe that can conduct sonar mapping and other readings under the ice. The remotely-operated Submersible Capable of under-Ice Navigation and Imaging (SCINI) has sent back spectacular photographs from the frigid ocean. The largest and most capable is ARTEMIS, an autonomous vehicle that can measure pH and oceanic currents as well as test for microbiological communities in the sub-Antarctic world. Data collected from their operation will certainly come in handy once space agencies are ready to peer below the frozen crust of a distant moon.
What will a future robotic probe see? At this point, nobody knows. But in addition to diving through the inky oceans of a frozen world, these pioneers should certainly check out the strange and unique locations at the bottom of the ice.