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Could the vast, long-hidden oceans be teeming with alien life in our own Solar System?
A new chapter in humanity’s search for extraterrestrial life opens on Thursday when the European spacecraft JUICE sets 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 have long been dismissed as possible candidates for hosting life in our backyard.
Until recently, the Solar System’s habitable zone was thought to “end up on Mars,” French astrophysicist Athena Coustenis, one of the European Space Agency’s (ESA) chief scientist for the JUICE mission, told AFP.
But NASA’s Galileo probe to Jupiter in 1995 and the more recent voyage of the Cassini spacecraft to Saturn have caused scientists to broaden their horizons.
The gas giant planets themselves have been correctly ruled out, but their icy moons, notably Jupiter’s Europa and Ganymede, and Saturn’s Enceladus and Titan, have offered new hope for nearby life.
Underneath 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 we’ve explored 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 told AFP earlier this year.
– ‘Gigantic’ ocean –
The Jupiter Icy Moons Explorer (JUICE) mission launched Thursday from Europe’s Kourou Spaceport in French Guiana on an eight-year odyssey through space.
By July 2031 it will have entered Jupiter’s orbit, from where it will be probing Ganymede, Europa and its icy companion moon Callisto.
Then, in 2034, JUICE will enter Ganymede’s orbit, the first time a spacecraft has done so around a moon other than ours.
Besides being the largest moon in the Solar System, Ganymede is also the only one to have its own magnetic field, which protects it from harmful radiation.
This is just one of many signs that Ganymede’s hidden ocean could provide a stable environment for life.
Unlike similar missions to Mars, which focus on finding signs of long-extinct ancient life, scientists hope Jupiter’s icy moons may still harbor living organisms, even if only tiny or single-celled.
Such habitability requires an energy source. In the absence of 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 heats the interior of the moons and keeps their water liquid.
Ganymede’s “gigantic” liquid ocean is trapped between two thick layers of ice tens of kilometers below the surface, said Carole Larigauderie, JUICE project manager at French space agency CNES.
“On Earth, we still find life at the bottom of the abyss,” he added.
Tiny microbes like bacteria and archaea have been found to be able to survive on Earth without sunlight, raising hopes that life elsewhere might do the same.
In addition to water and energy, life needs nutrients.
“The big question then is whether Ganymede’s ocean contains” the necessary chemical elements, Coustenis said.
The ocean should be able to absorb nutrients from anything that falls on the moon’s surface, for example, which would eventually dissolve into water, he added.
– Not Alone –
JUICE’s array of instruments will probe Ganymede’s ocean to determine its depth, distance from the surface and hopefully its composition.
ESA’s €1.6 billion ($1.7 billion) spacecraft will spend eight months orbiting Ganymede, getting within 200 kilometers (125 miles) of the moon, all while shielded from radiation.
It won’t be the only spacecraft lurking around Jupiter.
NASA’s Europa Clipper mission is scheduled to launch in October next year. It will take a faster path to Jupiter, arriving at Europa in the 2030s.
If one or more of Jupiter’s moons ticks all the boxes for hosting life, the “logical next step” would be to send a mission to land on the surface, said Cyril Cavel, JUICE project manager at the manufacturer Airbus.
While there are no plans for such a mission, which could definitively prove the existence of life beyond Earth, “it’s part of the dream,” he said.
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