Saturn’s icy moon Enceladus may be more habitable than thought

Saturn’s frozen moon Enceladus could be more supportive of life than previously thought, according to studies by planetary scientists that found conditions beneath its icy surface may allow certain microorganisms to survive.

The findings add to growing scientific interest in Enceladus as a potential location for finding life beyond Earth. Although the moon is far from the Sun and covered by an icy crust, scientists believe it contains a liquid ocean beneath its surface, BBC's Sky at Night Magazine writes. 

Studies of data collected by NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017, have previously detected complex organic molecules in material erupting from beneath Enceladus’s frozen crust.

Ice particles could preserve signs of life

Cassini conducted several “plume dives”, flying through water vapour erupting from Enceladus. The spacecraft’s instruments detected organic molecules in the material, which are considered building blocks of life.

In a new study, a team from Freie Universität Berlin examined how droplets of water from Enceladus’s subsurface ocean behave as they freeze and are expelled into space.

Scientists had previously believed the droplets would freeze almost immediately. However, the researchers found that freezing occurs more slowly, allowing salts and organic materials to separate and become concentrated in different parts of individual ice particles.

For example, sodium chloride, or table salt, can separate from sodium carbonate during the process.

The droplets can travel toward the surface at speeds of up to 1,000 kilometres per hour. When they collide with the walls of cracks in the ice, they can fragment into particles only a few micrometres across before being expelled into space.

As a result, individual ice grains may contain concentrated samples of particular substances from the ocean.

"Enceladus actually does a lot of the work for us in preparing samples for analysis that usually take a lot of effort in chemical labs on Earth," says Postberg, who led the study.

"The oceanic constituents are separated from each other and simultaneously concentrated into individual ice particles."

The researchers say this process could improve the chances of detecting biosignatures — chemical indicators that could point to the presence of life.

If material from microorganisms were present in one of the droplets, it could become concentrated within individual ice particles as the droplets freeze.

"That is great news in the search for life," says Postberg. "Future spacecrafts will have to analyse many individual ice particles in the plume.

"But if they come across one with microbial material in it, they could identify biosignatures in the particle relatively easy with already available technology."

Microorganisms survive simulated Enceladus conditions

A second study, involving scientists from Ludwig-Maximilians-Universität München and researchers from Freie Universität Berlin, tested whether microorganisms could survive conditions thought to resemble Enceladus’s ocean.

The researchers recreated an environment with low oxygen, high carbonate concentrations and high alkalinity. They then introduced Methanothermococcus okinawensis, a microorganism found near deep-sea hydrothermal vents on Earth.

The microorganism does not require oxygen and continued growing in the simulated Enceladus environment. It produced methane using hydrogen generated through water-rock reactions and adapted its metabolism to low concentrations of carbon dioxide.

"This was really a surprise to us," says Khawaja. "This was an experiment for which we did not expect such a successful outcome."

"On Enceladus the specific geochemical conditions might allow one of the oldest known metabolic systems on Earth to work, even in very alkaline environments," says Postberg.

The researchers stress that the findings do not prove life exists on Enceladus.

"While that doesn’t mean that there is life on Saturn’s moon, our first study shows that – in the event that there is – future space missions might have a good chance of finding traces if they analyse individual ice grains from Enceladus’s plume."

By Sabina Mammadli