The Galileo spacecraft may be dead, but it still has stories to tell. Fifteen years after the NASA probe burned up in Jupiter’s atmosphere, newly analyzed magnetic and plasma data from the mission have bolstered evidence that Europa, the planet’s ice-bound moon, is likely venting water into space.
Researchers have long believed that Europa is home to a vast saltwater ocean, trapped beneath a thick crust of ice, making the moon potentially habitable for life and a focus of upcoming robotic exploration. Over the past decade, scientists using the Hubble Space Telescope have made observations that seemed to support the notion that Europa is venting some of this water to space, much like Saturn’s moon Enceladus. But many other attempted observations have turned up dry.
So scientists instead returned to Galileo, which on 16 December 1997 made its closest approach to Europa, flying only 400 kilometers above its surface. Over the course of 5 minutes, spikes the spacecraft recorded with its magnetic and plasma sensors reflected the alterations that a veil of ejected water, from one or many vents, could cause in a region matching the telescope observations, they report today in Nature Astronomy. This indicates that a region of the moon potentially 1000 kilometers long could host such activity, though it is impossible to say whether this is a single plume or many, like the complex system of fractures and vents seen on Enceladus. Indeed, on its own, this evidence was too weak to tie to erupting water in a 2001 study describing it, the authors add, but it fits well with the Hubble and modeled evidence.
NASA’s Europa Clipper spacecraft, set for launch as soon as 2022, will carry several instruments capable of capturing and analyzing plume ingredients. If such an eruption does exist, it will make exploration of the ocean dramatically easier. The mission’s primary sponsor in Congress, Representative John Culberson (R–TX), could not hold back his glee last week in a hearing for a spending bill that supported the mission—breaking the journal’s embargo in the process: “The science community has wanted to go there for years, Mr. Chairman,” Culberson said, “and this bill makes that happen.”