A new chapter in the search for extraterrestrial life is to open today as Europe’s Jupiter Icy Moons Explorer (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, the ice-covered moons are so far from the sun that they were long dismissed as possible candidates to host life.
Until recently, the solar system’s habitable zone was thought to “end at Mars,” said French astrophysicist Athena Coustenis, one of the scientific leads of the European Space Agency’s (ESA) JUICE mission.
Photo: AFP
However, 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 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.
Nicolas Altobelli, a JUICE project scientist at the 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 told reporters earlier this year.
The JUICE mission is to launch from Europe’s spaceport in Kourou, French Guiana, today on an eight-year odyssey through space.
By July 2031 it is to enter Jupiter’s orbit, from which it would probe Ganymede, Europa and fellow icy moon Callisto.
Then, in 2034, JUICE would enter the orbit of Ganymede, the first time a spacecraft has done so around a moon other than the Earth’s.
As well as being the largest moon in the solar system, Ganymede is also the only one that has its own magnetic field, which shields it from 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,” Larigauderie said.
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.
JUICE’s array of instruments would probe Ganymede’s ocean to determine its depth, distance from the surface and its composition.
It would not be the only spacecraft lurking around Jupiter.
NASA’s Europa Clipper mission is scheduled to launch in October next year. It has a quicker path planned to Jupiter, arriving at Europa in 2030.
If one or more of Jupiter’s moons ticks all the boxes to host life, the “logical next step” would be to send a mission to land on the surface, said Cyril Cavel, JUICE project manager at manufacturer Airbus.
Although there are no plans for such a mission, “that’s part of the dream,” Cavel said.
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