Future missions to Europa could confirm if conditions for life exist on the icy moon. (Credit: NASA/JPL/University of Arizona)

Europa is covered with a cracked and jumbled shell of ice, suggesting the Jovian moon harbors liquid water­—and the potential for life. But most knowledge of Europa comes from the Galileo mission to Jupiter, which ended in 2003.

The question of Europa’s habitability has been frozen in debate for years. Its ice makes it an enticing target for unmanned space missions, yet the Jupiter Europa Orbiter (JEO) mission has suffered from funding fits and starts.

However, scientists are now considering a leaner mission to Europa – one that would still look for the characteristics of water, chemistry and energy that could be ingredients for life in the moon’s cold ocean.

Monday morning, in a presentation at the American Geophysical Union’s Fall Meeting, Robert Pappalardo, a senior research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., presented two complementary, money-saving mission possibilities.

An orbiter around Europa could take a holistic, big-picture look at the moon’s ocean and geology, while flybys from a spacecraft orbiting Jupiter could use ice-penetrating radar to peer into the ocean layers, Pappalardo says.

Flybys would answer the question: “Does Europa’s ocean have the chemical energy that would allow for life?”

On Europa, oxygen frozen onto its surface comes from charged particles hitting the moon and breaking ice into oxygen and hydrogen. If that oxygen could make its way into Europa’s ocean, it would be “great for life,” Pappalardo says. Those life forms could look like extremophiles — microbes that exist in Earth’s most inhospitable environments like Antarctica or near deep-sea thermal vents. Anything that lives beneath a radiation-bombarded ice shelf on a moon as cold as -200°C would have to be extreme by our standards.

A new analysis from Galileo data has helped thaw the debate about Europa’s habitability. For years, the thickness of Europa’s ice, and thus its potential to harbor life, has been hotly contested. But work presented in a separate session at the meeting suggests Europa is geologically active and liquid water could exist near the surface of the moon’s ice layer.

While those findings could help direct future Europa science, only a new mission will confirm that the moon’s ocean and frozen icey shell are creating the conditions for life, some scientists say – and it would be worth the trip.

“Europa is arguably the most likely place off of Earth to find life today,” Pappalardo says – at least in this solar system.

– Sarah Jane Keller is a science communication graduate student at UC Santa Cruz