Designing a rover to trundle over the arid surface of Mars is challenging enough, but building a robot that can explore the ocean depths of faraway moons is an arguably trickier task.

Scientists now believe that watery worlds like Enceladus - which orbits Saturn - or Jupiter’s moon Europa, hold the best conditions for finding alien life in the Solar System.

While upcoming Mars missions may uncover fossils of ancient life forms dating back billions of years, living organisms could still be thriving in the seas of volcanically active satellites. 

Hunting for extraterrestrial life in uncharted alien oceans is fraught with problems, not least because any probe must navigate solo beneath ice sheets that could be up to 12 miles thick, through which no signal could penetrate. 

But now Nasa has developed its first aquatic rover which can drive upside down under the sea ice, and is due to begin testing in the Antarctic.

Dubbed ‘Bruie’ which stands for Buoyant Rover for Under-Ice Exploration, the two-wheeled machine has been developed by Nasa’s Jet Propulsion Laboratory (JPL) in Pasadena.

Kevin Hand, JPL lead scientist on the Bruie project, believes that Europa and Enceladus, are the best chance of finding life.

“The ice shells covering these distant oceans serve as a window into what’s below, and the chemistry of the ice could help feed life within those oceans,” he said,

“Here on Earth, the ice covering our polar oceans serves a similar role, and our team is particularly interested in what is happening where the water meets the ice.”

Related Slideshow: Are aliens out there? These 16 signs may surprise you (Provided by Photo Services)

Three feet long and equipped with toothed wheels to dig into the underside of the ice-sheet, the floating rover can take images and collect data at the crucial region where water and ice meet - an area scientists call the ‘ice-water interface.’

“We've found that life often lives at interfaces, both the sea bottom and the ice-water interface at the top,” added lead engineer Andy Klesh.

“Most submersibles have a challenging time investigating this area, as ocean currents might cause them to crash, or they would waste too much power maintaining position

“Bruie, however, uses buoyancy to remain anchored against the ice and is impervious to most currents.”

The rover can also power down, turning itself on when it needs to take measurements, meaning it could spend months observing conditions under the ice. 

Testing is scheduled to take place on lakes near the Australian Antarctic Progamme’s Casey station in the coming weeks.

Scientists will drill holes into the ice and send the tethered rover down beneath the ice so they can safely test its suite of gadgets, including two high definition live cameras. 

The rover will also carry several instruments to measure parameters related to life, such as dissolved oxygen, water salinity, pressure and temperature.

However scientists have warned that still may not be enough to detect life on another world. 

“We only really know how to detect life similar to that on Earth,” said mechanical engineer Dan Berisford of the University of Western Australia, who is one of the testing team. 

“So it's possible that very different microbes might be difficult to recognize.”

The team will continue to work on Bruie until it can survive under the ice for months at a time, remotely navigate without a tether and explore the ocean at greater depths.

Scientists have been keen to explore ocean worlds since Nasa’s Cassini spacecraft detected the first evidence of chemical reactions deep below the ice crust of Enceladus which could be creating an environment capable of supporting microbes. 

Some 887 million miles from the Sun, Enceladus should be a frozen inhospitable wasteland, but scientists believe volcanic activity beneath the ice sheets keeps it warm enough for life.

Likewise the Jovian moon Europa, also has liquid oceans and could harbour organisms, scientists believe.

Nasa is already at work constructing the Europa Clipper orbiter, which is scheduled to launch in 2025, laying the groundwork for a future mission that could search for life beneath the ice.