How do you solve a problem like Europa? We are almost certain there is a vast and potentially habitable ocean of water beneath the icy crust of this moon of Jupiter, but actually getting there and exploring it poses a problem. NASA’s latest concept vehicle, though, might be a partial solution.

A team of scientists from NASA's Jet Propulsion Laboratory (JPL) has been testing a buoyant rover, called the Buoyant Rover for Under-Ice Exploration (BRUIE), that can drive “upside down” on ice. When placed in water beneath an ice shelf, the rover floats to the top, and then uses two wheels to drive on the underside of the ice “ceiling.” A suite of cameras, lights, and instruments can then be used to study the water below.

In a video, NASA explains how it took the rover to the thick ice shelf of the Arctic, specifically to Barrow, at the northernmost point of Alaska. This is thought to be a good analogue for Europa, with the vast ocean and thick ice mimicking what the moon could look like beneath its surface.

^{Check out the video of the rover in action above. NASA/JPL.}

The purpose of this mission wasn’t just to test technologies for other worlds like Europa or even similar ocean-harbouring worlds like Saturn's moon Enceladus. The scientists also hope to study the methane that is trapped in these lakes and coming out of the permafrost, to see how such greenhouse gas emissions are affecting Earth's climate. The cameras on the rover were able to look down at the lake bed, mapping out some seeps of methane that were forming.

It’s unlikely such a rover will see the bed of Europa’s ocean, which could be tens to hundreds of miles deep. But the instruments on board would be able to observe what happens at the point where the water meets the ice – and probe partially into the depths.

^{Mars is cool. Europa is better. Shown is an artist's impression of its underground ocean. NASA.}

At first, the team used a tether to communicate with the rover while it was under the ice. But ultimately they went wireless; Kevin Hand, a JPL planetary scientist and astrobiologist, noted in the video that “if we do eventually deploy in a world like Europa, we’re not gonna have a tether.”

The rover was able to communicate through the ice and, simulating a Europa mission, these communications were relayed through a satellite back to operators at JPL. Of course, the icy crust on Europa is much thicker, so the logistics of communicating from its ocean will be considerably more difficult. And getting through the ice in the first place is a problem without a solution at the moment.

Key to any such mission will be studying Europa in more detail, to ascertain the thickness of the ice and ocean. NASA is planning to do just that in the 2020s with their Europa Multiple-Flyby Mission, which will use radar to study the interior of the moon. It will likely be left to a future mission to explore beneath the surface – and who knows, perhaps this rover will be the vehicle that does it. 

So while dribbles of water on Mars are all well and good, let’s not forget there is an ocean containing more water than there is on Earth just waiting to be explored on Europa.