Scientists say Jupiter's moon Europa may support life.
Nasa scientists have begun work on a $2bn space probe that will look for evidence of life on one of Jupiter's moons.
The probe would be the first dedicated mission to Europa, a moon whose vast oceans are buried under sheets of permafrost.
The 'Clipper' probe could be launched by 2021 and would take three to six years to arrive on Europa.
"On Earth, everywhere where there's liquid water, we find life," said Robert Pappalardo, a senior research scientist at Nasa's jet propulsion laboratory in California, who led the design of the Clipper.
"The search for life in our solar system somewhat equates to the search for liquid water. When we ask the question 'where are the water worlds?', we have to look to the outer solar system because there are oceans beneath the icy shells of the moons."
The ice-bound moon is thought to be the most likely place in our solar system to support life, due to the chemical and environmental properties of its eco-system.
Jupiter's biggest moons, Ganymede, Callisto and Europa, have liquid oceans beneath their blankets of ice, and are warmed as they orbit the planet.
With its extreme radiation levels, Europa is also likely to have an abundance of oxidants that could support lifeforms.
"We generally focus down on Europa as the most promising in terms of potential habitability because of its relatively thick ice shell, an ocean that is in contact with rock below, and that it's probably geologically active today," Pappalardo told the American Association for the Advancement of Science in Boston.
The probe would make several flybys of Europa as it orbited Jupiter, giving it "global coverage" of the moon, Pappalardo said, much as the successful Cassini probe had done for Saturn's moon Titan.
"Part of Nasa's mission is to go explore and that should include places that are an extremely high scientific priority," Pappalardo said.
"It really is one of the most profound questions we can ask. Is there life elsewhere in the solar system?"
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