Why NASA is sending a probe to Europa – and what it’s looking for

Seen against the backdrop of Jupiter’s dramatic, swirling atmosphere, Europa might at first appear a bit drab. With its greyish-white surface, you might even say it resembles a well-worn cue ball in a run-down pool hall. On closer inspection, however, the Jovian system’s fourth-largest moon is shimmering with intrigue from deep within.

From what we can tell, its icy outer layer conceals a vast global ocean containing twice the volume of water on Earth. This, in addition to hints of geophysical activity – such as the rusty lines that streak its surface – and complex chemistry, is why Europa has long captivated astronomers searching for habitable worlds beyond our pale blue dot. So could Europa have the conditions for life? We’re about to find out.

In October, NASA will launch Europa Clipper, a $5 billion probe that will get a closer look at the moon’s geology and chemistry – and, with any luck, identify the telltale signatures of habitability. The mission has been decades in the making, building on previous forays that have thrown up tantalising clues as to what lurks inside the moon’s frozen shell – and no shortage of questions.

Clipper promises answers. It will study the moon’s surface and the ocean hidden beneath in unprecedented detail. It could even sample the water in plumes of vapour if, as we suspect, they are erupting from Europa’s surface. And although it isn’t designed to find direct evidence of life – a bacterial cell, say – recent developments suggest there is a fleeting chance it could do exactly that. “With Europa Clipper, we’re really entering…