Conditions ideal for alien life could exist on icy moons of Saturn and Jupiter

A robotic space probe has discovered that there are conditions ideal for alien life to thrive on at least one moon in the outer Solar System, NASA announced today. And Hubble Space Telescope observations suggest similar conditions might exist on another.

Geysers on Enceladus
An artist’s concept of the salty spray erupting in geysers from the south polar cracks of Enceladus. Image credit: NASA/JPL-Caltech

NASA’s robotic Cassini spacecraft has made several dives through geysers spouting salty water from the south polar region of one of Saturn’s moons, Enceladus.

Cassini’s instruments tasted the spray erupting from cracks in the surface ice on Enceladus and discovered the presence of molecular hydrogen, which provides an energy source for potential life.

Scientists say the only plausible source of this hydrogen is a hydrothermal chemical reaction caused by water in an underground ocean rubbing against hot rocks. They also found some carbon dioxide. The two ingredients are important for a process called methanogenesis that allows microbial life to be found deep in Earth’s own oceans.

Enceladus’s 30km deep subterranean sea is believed to extend right the way around the moon, just below its icy crust. Saturn lies around 1.2 billion km from the Sun, so is far beyond what is generally regarded the habitable zone.

But despite being in the frozen outer part of the Solar System, the ocean of water on Enceladus is kept a warm liquid because of the churning caused by giant planet Saturn’s gravitational pull.

Enceladus graphic
This graphic illustrates how scientists on NASA’s Cassini mission think water interacts with rock at the bottom of the ocean of Saturn’s icy moon Enceladus, producing hydrogen gas. Image credit: NASA/JPL-Caltech/Southwest Research Institute

Nasa scientists say the reaction caused by the water rubbing against the rocks has a similar effect to that seen deep in our own oceans where, despite the absence of sunlight, living microbes can be found thriving around hydrothermal vents in the rocks.

They say that the chemistry going on in Enceladus’ underground ocean makes the environment a potentially habitable one. That is not the same as saying it is inhabited, but the possibility is an exciting one.

“Hydrogen is a source of chemical energy for microbes that live in the Earth’s oceans near hydrothermal vents,” said Dr Hunter Waite, of the Southwest Research Institute (SwRI), and principal investigator of Cassini’s Ion Neutral Mass Spectrometer (INMS).

“Our results indicate the same chemical energy source is present in the ocean of Enceladus. We have not found evidence of the presence of microbial life in the ocean of Enceladus, but the discovery of hydrogen gas and the evidence for ongoing hydrothermal activity offer a tantalizing suggestion that habitable conditions could exist beneath the moon’s icy crust.”

Europa spouts geysers too

Other moons orbiting the outer planets have also been found to have underground oceans. Last year, the Hubble space telescope detected geysers similar to those on Enceladus erupting from one of Jupiter’s moons, Europa.

NASA is planning to launch a mission in 2022, called Europa Clipper, to orbit and land on Europa to discover whether it might be home to alien life.

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Europa’s underground sea, discovered by NASA’s Galileo probe in the 1990s, may be more than 100km deep, and hold twice as much water as all the Earth’s seas put together. The latest findings are published in the journal Science.

NASA video explaining the significance of the discovery

Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at Headquarters in Washington, said in a statement: “This is the closest we’ve come, so far, to identifying a place with some of the ingredients needed for a habitable environment.”

The research suggests that these outer moons now may offer a better chance for discovering life than former favourite Mars, which has little if any liquid water plus a surface bombarded by radiation which would be harmful to life.

NASA’s video about the prospects for life on moons with underground oceans

By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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