Scientists have recently discovered fish living under 740 meters of ice in Antarctica: This has caused speculation about the possibility of extraterrestrial life in places like Jupiter’s moon, Europa, which likely harbors an ocean of liquid water beneath a crust of ice.

Astrobiologists are excited about the possibility of someday finding microbial slime on the underside of Europa’s ice. But the Antarctica find is suggestive of the idea that more complex forms of life may call that extreme environment home.

“The question will always be energy,” says Georgia Institute of Technology planetary scientist, Britney Schmidt. “Fish require a lot of energy—a lot more than microbes.”

In order for fish to thrive, a multilevel ecosystem must exist. . At the bottom of an aquatic ecosystem, single-celled microbes use energy from sunlight or chemical sources to take in carbon dioxide molecules. The microbes are eaten by microscopic creatures called protists and in the case of the Antarctic ecosystem, crustaceans eat them. At the top of this food chain are fish that eat the crustaceans.

John Priscu is a microbial ecologist from Montana State University who was part of the team that discovered the Antarctic fish this month. He says the transfer of energy up the food web is inefficient. “You lose about 90 percent of the energy as you go [each step] up a food web,” he says. This means that for every kilogram of fish in the ecosystem, 1,000 kilograms of microbes at the base of the food web may be required. If the newly discovered fish eat the microbes directly, that number falls to at least 10 kilograms of microbes per kilogram of fish. The energy needs of the fish involved, as well as the energy available in their environment, will determine if life could exist on Europa.

Studies of lakes sealed beneath hundreds of meters of Antarctic ice have provided a viable answer to the question of how life forms might find energy on Europa.  Most ecosystems on Earth are powered by sunlight, which fixes carbon via photosynthesis. But any life under 10 or 20 kilometers of ice would need to find another way.

In January 2013 the team that discovered the ocean fish in Antarctica also drilled into the subglacial Lake Whillans, Both projects were sponsored by the National Science Foundation. The lake is about 100 kilometers inland from where the fish were discovered and sits under 800 meters of ice. Researchers found a thriving ecosystem with 130,000 microbial cells per milliliter of water. Interestingly, the environment was as warm as the surrounding ocean and contained levels of oxygen that some marine animals can survive on.

According to scientists, the oxygen comes from the ice shelf. Ambient geothermal heat from the seafloor melts the underside of the ice sheet, freeing air bubbles that were trapped in the ice as it formed thousands of years ago.

Genetic studies have led researchers to believe the microbes use ammonium and iron minerals for carbon fixing. Jet Propulsion Laboratory astrobiologist, Kevin Hand, believes that system also exists on Europa. Spectral readings Keck Observatory telescopes in Hawaii have found high levels of oxidative chemicals on Europa’s surface. This is the result the surface being scoured by Jupiter’s ionizing radiation. Living organisms could use these oxidizing chemicals to burn fuels seeping up from the bottom of Europa’s ocean. This is possible because Europa seems to be geologically active, allowing fuel and oxidants to be transported, mixed and constantly renewed.

NASA is engaged in a mission called Europa Clipper, address these questions using a reconnaissance spacecraft in orbit around Jupiter . Clipper will periodically swoop down 25 to 100 kilometers above Europa’s surface and use ice-penetrating radar to measure the thickness of the ice shell.  It will also map the area below the ice and find pockets of water. An onboard magnetometer will measure the depth and saltiness of the ocean and a spectrometer will measure chemicals in Europa’s uppermost layers of ice. Assuming it is properly funded, Clipper will take years to build.

Questions remain about various aspects of the find but scientists are confident they will find the answers. They are hoping for more NSF funding to keep pursuing the intriguing puzzle of life beyond our world.