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Enceladus, methane, and the possibility of extraterrestrial life

Enceladus, though tiny, also hides a liquid water ocean beneath an icy shell. A sign of life?

Enceladus is the sixth-largest moon of Saturn. Image by NASA/JPL/USGS
Enceladus is the sixth-largest moon of Saturn. Image by NASA/JPL/USGS

Scientists continue to search for life on other planets and moons in our Solar System. There are some contenders: Jupiter’s Europa and Saturn’s Enceladus, despite their frozen, forbidding surfaces, are hiding vast oceans beneath the ice – among several moons with subsurface oceans and hence there is the possibility of some form of microbial life being present.

Research, arising from the University of Arizona, suggests geochemical processes, as currently known, do not offer an adequate explanation for the levels of methane measured by the Cassini spacecraft on Saturn’s icy moon.

The inference is that conditions for life may exist on Enceladus, since the data is consistent with microbial activity similar to that known to occur at hydrothermal vents in Earth’s oceans. However, it is important to note that similar conditions do not mean that life does exist, only that it could exist.

Enceladus is the sixth-largest moon of Saturn. The satellite is about 500 kilometers in diameter, about a tenth of that of Saturn’s largest moon, Titan. Enceladus is covered by fresh, clean ice and it appears as a highly reflective object within the Solar System. The moon has some remarkable characteristics; for example, buried beneath 20 kilometers of ice, the subsurface ocean of Enceladus appears to be churning with currents akin to those on Earth. This subsurface ocean produces regular geyser-like eruptions.

By travelling through the plumes and by sampling the chemical makeup, Cassini detected a relatively high concentration of specified molecules that are associated with hydrothermal vents on the bottom of Earth’s oceans. Of interest were dihydrogen, methane, and carbon dioxide. Of these, the amount of methane found in the plumes was regarded by the science team as particularly unexpected

Cassini was the fourth space probe to visit Saturn and the first to enter its orbit. While the data from the mission continues to be assessed, scientists have already discovered propeller-like formations on Saturn, witnessed the possible birth of a new moon and observed the most active, chaotic rings within the Solar System (this is Saturn’s F ring).

The finding leads to the theoretical possibility that Earth-like bacteria (such as methanogens) that function to ‘eat’ dihydrogen and produce methane. Such a presence may explain the surprisingly large amount of methane detected by Cassini.

The possibility arises from analyzing the collected data from the perspectives of geochemistry and microbial ecology. A model based on these inputs , based on a given set of chemical conditions, such as the dihydrogen concentration in the hydrothermal fluid, plus readings of temperature, finds that the conditions could provide a suitable environment for certain bacteria to thrive.

The presence of the right chemical mix might be a consequence of Enceladus most likely having been formed through the accretion of organic-rich material supplied by comets during the earlier days of the Solar System.

The research appears in the journal Nature Astronomy, titled “Bayesian analysis of Enceladus’s plume data to assess methanogenesis.”

Written By

Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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