SET THE JUICE LOOSE

This month, the JUICE mission blasts off on its eight-year voyage to Jupiter. Once there, it will peer at the planet's moons to find out if life could be lurking beneath their icy crusts...

- DR LOUISA PRESTON

The Earth has always been believed to be the gold standard for a habitable world. Lessons learnt from life on Earth have told us that if we want to seek life on other planets in the Solar System, we need to find three basic ingredients in the same place at the same time – liquid water, the chemical building blocks of life, and a source of energy. Previously, we thought that these could only be found within a narrow ring around the Sun called the ‘Goldilocks Zone’, or ‘Habitable Zone’. But we were wrong. 

Images of Jupiter’s moons taken by the Voyager missions in 1979 and the Galileo spacecraft between 1995 and 2003 completely reshaped our view of the Solar System.

They exposed evidence for liquid water in the outer reaches of our planetary neighbourhood, far from where we thought it should be able to exist. Today, we know that the fourth largest moon of Jupiter, Europa, contains more water than all of Earth’s oceans combined. It turns out that Jupiter, despite being outside our Solar System’s traditional habitable zone, has created a habitable zone all of its own, driven not by the Sun’s warmth – sunlight at Jupiter is 30 times dimmer than at Earth – but by the effects of its incredibly powerful gravity. Given these new ‘cooler’ habitable options, in April this year the JUpiter ICy moons Explorer (JUICE) mission will be sent to Jupiter’s moons to help astrobiologists understand how habitable worlds have emerged in the outer Solar System.