Saturn's moon Enceladus shows potential for habitability

Artist’s impression of thermal jets venting through the icy surface at the southern polar region of Saturn’s moon Enceladus. Credit: ESA/Science Office

The Cassini spacecraft revealed incredible insights into Saturn and its moons over its 20-year mission, from the planet’s remarkably young rings to its moons’ violent origins.

Now, almost 20 years after Cassini flew through plumes of water bursting from cracks in the icy surface of Saturn’s moon Enceladus, new data analysis has confirmed that complex chemical reactions are taking place within the moon’s hidden ocean.

The findings affirm Enceladus has all 3 conditions for a habitable environment to potentially support life as we know it: the presence of liquid water, a source of energy, and a specific set of chemical elements.

The jets of vapour eject from fissures close to the moon’s south pole, sending grains of ice into space where they fall back to the surface or escape to form a ring around Saturn.

Light, soluble and reactive organic molecules making their way onto ice grains emitted in jets of water from Saturn’s moon Enceladus. Credit: NASA/JPL-Caltech

Study lead author Nozair Khawaja from Germany’s Free University of Berlin explains: “Cassini was detecting samples from Enceladus all the time as it flew through Saturn’s E ring. We had already found many organic molecules in these ice grains, including precursors for amino acids.”

But the ice in Saturn’s E ring can be hundreds of years old. This raised the possibility that the molecules had been altered by intense space radiation after they emerged from the planet’s surface.

The team needed younger samples to confirm the organic molecules were created within Enceladus’ ocean.

The new study analysed data collected by Cassini as it flew through a fresh spray in 2008. The grains of ice, just minutes old, hit Cassini’s Cosmic Dust Analyser instrument at speeds of 18km/s.

How we think hydrothermal activity works on Enceladus, based on data from the NASA/ESA Cassini-Huygens mission. Credit: ESA

Organic molecules found in the E ring were also present in the fresh ice grains alongside newly detected molecular fragments including, potentially, nitrogen- and oxygen-bearing compounds.

“These molecules we found in the freshly ejected material prove that the complex organic molecules Cassini detected in Saturn’s E ring are not just a product of long exposure to space, but are readily available in Enceladus’ ocean,” says co-author Frank Postberg, also from the Free University of Berlin.

“There are many possible pathways from the organic molecules we found in the Cassini data to potentially biologically relevant compounds, which enhances the likelihood that the moon is habitable,” adds Khawaja.

“There is much more in the data that we are currently exploring, so we are looking forward to finding out more in the near future.”