A billion-euro mission to look for signs of life on the frozen moons of giant planet Jupiter was given the go-ahead today. The European Space Agency will send an unmanned probe called Juice – short for Jupiter Icy Moons Explorer – to study liquid oceans that are thought to lie under their surface and which could be home to aquatic aliens. 

An international science team will include UK scientists from universities in Oxford, Leicester and London who have helped design the mission which will check the waterworlds for habitability.

Juice is the first Large-class mission chosen as part of ESA’s Cosmic Vision 2015-2025 programme. Visits will be made to Jupiter’s three biggest moons, Ganymede, Callisto and Europa which were first discovered by Galileo in 1610 along with a volcanic moon called Io.

Ganymede, which is eight per cent bigger than the planet Mercury, is the prime target. A deep ocean is thought to lie under its icy crust, kept warm by Jupiter’s powerful tidal forces. The moon is also interesting because it generates its own magnetic field plus it has a cratered surface that is more varied than on any other body in the Solar System.

The space probe is due to launch in 2022 from Europe’s spaceport in Kourou, French Guiana, on an Ariane 5 but will not arrive at the Jupiter system until 2030. Juice will carry experiments to examine the ocean, plus the make-up of Ganymede’s surface. Jupiter-type planets have been found to be common around other stars and so space scientists are keen to know whether their natural satellites could be inhabitable by alien life.

Professor Alvaro Giménez Cañete, ESA’s Director of Science and Robotic Exploration, said: “Jupiter is the archetype for the giant planets of the Solar System and for many giant planets being found around other stars. Juice will give us better insight into how gas giants and their orbiting worlds form, and their potential for hosting life.”

Juice scientist Dr Leigh Fletcher of Oxford University, said: “Scientists have had a lot of success detecting the giant planets orbiting distant stars, but the really exciting prospect may be the existence of potentially habitable ‘waterworlds’ that could be a lot like Ganymede or Europa.

“One of the main aims of the mission is to try to understand whether a ‘waterworld’ such as Ganymede might be the sort of environment that could harbour life.’”

Chief scientist for Juice is Professor Michele Dougherty of Imperial College, London. She told the BBC today that she would be very surprised if there wasn’t some form of life out at Jupiter’s moons. She added: “Ever since Galileo’s discovery of the four largest moons of Jupiter, we’ve wondered what it must be like on their icy surfaces, looking into a night sky dominated by the gas giant Jupiter.

“From the volcanic moon Io, to the potential sub-surface oceans of Europa and Ganymede and the ancient cratered terrain of Callisto, these four moons are fascinating worlds in their own right.”

Juice was selected as ESA’s flagship mission in the next decade, beating two rivals, an X-ray observatory called Athena and a triple-satellite bid to detect gravitational waves.