Enceladus, one of Saturn's many moons, is one of the most promising places for exploration and astrobiology today. Like other "Ocean Worlds" in our Solar System, this moon has an ocean located between its icy surface and its rocky, metallic core. Due to tidal flexing in this core, the result of interaction with Saturn's gravitational pull, Enceladus also experiences hydrothermal activity at its core-mantle boundary.

With the success of the Cassini-Huygens mission, scientists hope to send a dedicated mission to explore Enceladus for signs of life. Recently, researchers from the Planetary Sciences and Remote Sensing group at Freie Universität Berlin published two studies examining the prospects of such a mission. They conclude that an Enceladus mission would have an easier time detecting biosignatures than previously thought, based on the dynamics of the moon's plumes.

The research was led by Prof. Frank Postberg and Dr. Vanessa Helmbrecht, researchers from the Institute of Geological Sciences at Freie Universität Berlin and the Department of Earth and Environmental Sciences at Ludwig-Maximilians-Universität, respectively. The results of their study are published in two papers that appeared in Science Advances.

What makes Enceladus an especially promising candidate is the plumes that regularly erupt from its southern polar region, sending ice particles hundreds of kilometers into space. NASA's Cassini spacecraft examined these plumes by flying through them during a series of flybys. During these encounters, Cassini detected salts and organic compounds, strong indications that the interior ocean could support life.

In their first study, the team showed that ocean droplets can freeze more slowly than previously thought as they move through cracks in Enceladus’ ice shell. As the droplets freeze, the salts and organic compounds they contain are distributed into different regions. These can then fragment as they are accelerated into space, creating ice grains that may contain highly concentrated substances, making biosignatures easier to detect.

In their second study, the team showed that methane-producing bacteria (methanogens) could survive and produce methane under simulated conditions present on Enceladus. These findings suggest that a probe passing through Enceladus' plumes could easily detect potential biomarkers that could result from life and biological processes in the interior.

These results will inform several missions currently in development, such as the proposed NASA Flagship mission called the Enceladus Orbilander. As the name suggests, this mission would spend a year and a half orbiting Enceladus and sampling its water plumes before landing on the surface for a two-year mission to study materials for evidence of life.

Similarly, the European Space Agency is working on its L4 Enceladus Mission, which was selected under the Voyage 2050 plan with a proposed launch date for the early 2040s. Like its NASA counterpart, this mission would conduct multiple flybys through the plumes and land at the south pole to analyze a geyser.

Breakthrough Initiatives also has a plan in place for a low-cost, privately funded mission: Breakthrough Enceladus. All of these efforts highlight the importance of Enceladus as an eventual destination for an astrobiology mission. As efforts to search for possible extraterrestrial life expand beyond Mars, and with missions bound for Jupiter, Saturn's little icy moon has already established itself as the next step.