Search for alien life extends to Jupiter’s icy moons

Could vast, long-hidden oceans be teeming with alien life in our very own Solar System? A new chapter in humanity’s search for extra-terrestrial life opens on Thursday as Europe’s JUICE spacecraft blasts off on a mission to investigate the icy moons of Jupiter.

First discovered by Italian astronomer Galileo Galilei more than 400 years ago, these ice-covered moons are so far from the Sun that they were long dismissed as possible candidates to host life in our backyard.

Until recently, the Solar System’s habitable zone was thought to “end at Mars”, French astrophysicist Athena Coustenis, one of the scientific leads of the European Space Agency (ESA)‘s JUICE mission, said. But Nasa’s Galileo probe to Jupiter in 1995 and the more recent Cassini spacecraft’s trip to Saturn caused scientists to broaden their horizons.

The gas giant planets themselves were correctly ruled out, but their icy moons — particularly Jupiter’s Europa and Ganymede, and Saturn’s Enceladus and Titan — offered fresh hope of nearby life. Under their icy surfaces are thought to be huge oceans of liquid water — a crucial ingredient for life as we know it.

Nicolas Altobelli, a JUICE project scientist at ESA, said it would be “the first time that we explore habitats beyond the frost line” between Mars and Jupiter.

Beyond that line, temperatures plummet and “liquid water can no longer exist on the surface”, Altobelli said earlier this year.

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‘Gigantic’ ocean

The Jupiter Icy Moons Explorer (JUICE) mission launches from Europe’s spaceport in Kourou, French Guiana on an eight-year odyssey through space. By July 2031 it will have entered Jupiter’s orbit, from which it will probe Ganymede, Europa and fellow icy moon Callisto.

Then, in 2034, JUICE will enter the orbit of Ganymede, the first time a spacecraft has done so around a moon other than our own. As well as being the largest moon in the Solar System, Ganymede is also the only one that has its own magnetic field, which protects it from dangerous radiation. This is just one of several signs that Ganymede’s hidden ocean could provide a stable environment for life.

Unlike similar missions to Mars, which focus on finding signs of ancient life long since extinguished, scientists hope Jupiter’s icy moons will still be home to living organisms, even if only tiny or single-celled.

Such habitability requires a power source. Lacking energy from the Sun, the moons could instead take advantage of the gravity that Jupiter exerts on its satellites.

The force creates a process called tidal heating, which warms the interior of the moons and keeps their water liquid.

Ganymede’s “gigantic” liquid ocean is trapped between two thick layers of ice dozens of kilometres beneath the surface, said Carole Larigauderie, JUICE project head at French space agency CNES.

“On Earth, we still find life forms at the bottom of the abyss,” she added.

Tiny microbes such as bacteria and archaea have been found to be able to survive on Earth without sunlight, raising hopes that life elsewhere will be able to do the same.

As well as water and energy, life needs nutrients.

“The big question is therefore whether Ganymede’s ocean contains” the necessary chemical elements, Coustenis said.