The European Space Agency (Esa) is to mount a billion-euro mission to Jupiter and its icy moons.

欧洲太空总署将斥资10亿欧元探险木星以及它的冰冷的卫星。

The probe, called Juice, has just been approved at a meeting of member state delegations¹ in Paris.

It would be built in time for a launch in 2022, although it would be a further eight years before it reached the Jovian system.

The mission has emerged from a five-year-long competition to find the next "large class" space venture in Europe.

Juice stands for JUpiter ICy moon Explorer. The concept proposes an instrument-packed, nearly five-tonne satellite to be sent out to the Solar System's biggest planet, to make a careful investigation² of three of its biggest moons.

The spacecraft would use the gravity of Jupiter to initiate³ a series of close fly-bys around Callisto and Europa, and then finally to put itself in a settled orbit around Ganymede.

Emphasis would be put on "habitability" - in trying to understand whether there is any possibility that these moons could host microbial life.

Callisto, Europa and Ganymede are all suspected to have oceans of water below their icy surfaces. As such, they may have environments conducive⁴ to simple biology.

"People probably don't realise that habitable zones don't necessarily need to be close to a star - in our case, close to the Sun," explained Prof Michele Dougherty, a Juice science team member from Imperial College London, UK.

"There are four conditions required for life to form. You need water; you need an energy source - so the ice can become liquid; you need the right chemistry - nitrogen, carbon, hydrogen; and the fourth thing you need is stability - a length of time that allows life to form.