NASA is gearing up to send a spacecraft to Europa, a moon of Jupiter that some scientists think is more likely to host extraterrestrial life than anywhere else in the solar system.

It won't be an easy mission — it will likely cost billions and the instruments will need a lot of testing before they can be sent on their long journey through space.

Reprocessed images taken by NASA's Galileo spacecraft in the late 1990s show brown streaks in the ice that appear to contain sulphur compounds. ( NASA/JPL-Caltech/SETI Institute)

Fortunately, scientists will have access to a great testing ground — a unique yellow glacier on Ellesmere Island in Nunavut that is more like Europa than any other known place on Earth.

It's an exciting time for scientists involved in the proposed Europa mission. Just this week, NASA administrator Charles Bolden announced in his state of NASA address that the U.S. space agency would be selecting instruments this spring for the unmanned spacecraft known as the Europa Clipper after the budget proposed by U.S. President Obama's administration committed continued funding for the mission.

Europa is considered by some scientists to be one of the most likely places in the solar system to host extraterrestrial, microbial life — more likely, even, than Mars.

Unmanned rover and orbiter missions to Mars have found ample evidence that it was a wet place in the past, and water still exists on the surface as ice. But there isn't much evidence that liquid water still exists on the surface of Mars today, a key requirement for life as we know it.

Meanwhile, so far, there is good evidence that Europa still hosts a liquid ocean beneath its icy crust.

'All the basics'

"It's one of the highest potential areas for finding life outside of Earth," says Steve Grasby, a geoscientist with the Geological Survey of Canada. "You have everything — energy, you have water, probably an ocean of similar salinity to that on Earth. You have all the basics you need."

Alexis Templeton of the University of Colorado eyes the yellow glacier on Ellesmere Island in Nunavut that is considered an environment similar to that on Europa. (Stephen Grasby/Natural Resources Canada)

Grasby, who has been studying the Ellesmere Island glacier for years, called the recent announcements about the Europa mission "very exciting."

No launch date has been set, but NASA's plan is for the spacecraft to perform 45 flybys of Europa, some as low as 25 kilometres above its surface. It would use radar to peer through and measure the thickness of the frozen crust of ice on the surface, photograph the surface with high-resolution cameras and use spectrometers to figure out what the surface of the moon and its trace atmosphere are made of.

The goal is to get a better idea of whether the icy moon could have conditions suitable for life.

So far, the conditions on Europa look to be very similar to those at the glacial spring at Borup Fiord Pass on Ellesmere Island, and that's promising.

The site was discovered by Grasby and University of Calgary geoscientist Benoit Beauchamp about 25 years ago when they were on a plane, conducting an aerial survey of a glacier-capped geological formation at about 81 degrees north, near the northern tip of Ellesmere Island. Suddenly, they spotted a huge patch of yellow material in the ice, "not unlike someone having peed in the snow," Beauchamp recalled.

When they landed to investigate, they were hit by the stench of rotting eggs, as the yellow stuff was sulphur compounds seeping out of a spring from minerals two kilometres below the surface.

That makes it unlike any other known glacier in the world, but uncannily similar to the environment on Europa. There, the ice is covered in brown streaks that also appear to be made of sulphur compounds.

Microbe home

In the years since the glacier was discovered, Beauchamp has studied the rocks the spring seeps through, and Grasby has tried to understand the processes that bring the sulphur to the surface. The site has also been studied by microbiologists who have found bacteria living and multiplying there, despite the cold, harsh environment.

Robert Pappalardo, project scientist for the Europa mission, says microbes he and his team collected from the spring are being studied to understand how they obtain food and energy in the ice. (NASA)

Robert Pappalardo, a project scientist for the Europa mission, says microbes he and his team collected from the spring are being studied to understand how they obtain food and energy in the ice.

"We're looking at one possible way that life in ice can survive and metabolize, and that gives us ideas for what might be possible in Europa."

Scientists from NASA and the University of Colorado have also taken ground measurements at the glacier and compared them to satellite measurements. That could help them gauge what the Europa Clipper might see — or miss — on its flybys.

Grasby says tests at the glacier could be very valuable ahead of the mission to make sure the right instruments are chosen for the spacecraft and to make sure scientists understand what kind of data those instruments are producing.

"If you want to look at signs of life in the sulphur glacier system," he said, "well, here's the best place on Earth we can study to see what those might be and what types of instruments might detect that."

Pappalardo said now that NASA has expressed continued interest in the Europa mission, his team hopes to do more tests at the Ellesmere Island glacier, but also to test a microscope that will be used to hunt for microbes in the hot springs of Axel Heiberg Island.