Water, water everywhere means we may soon find aliens

Scientists wonder if life could exist under the icy surface of Europa, one of Jupiter's moons. Photo / Nasa

Is there anyone out there? The answer is almost certainly yes, says a top Nasa scientist who believes we may know for sure within a decade.

The search for alien life has long since shifted from a question of whether it exists to a question of when we'll find it.

And Nasa's chief scientist Ellen Stofan predicted this week that the answer could be just a few years away.

"I believe we are going to have strong indications of life beyond Earth in the next decade and definitive evidence in the next 10 to 20 years," Stofan said at a panel on Wednesday, according to the Los Angeles Times.

The search has taken a number of forms, but one of the most important facets has been the task of searching the universe for signs of liquid water, which contains some of the essential building blocks of life as we know it.

So far, scientists have found plenty of evidence that water is, simply put, everywhere.

There is evidence to suggest that vast oceans could well be sloshing around under the surface of moons and dwarf planets within our own solar system. Mars might have once had an expanse of liquid water on its surface. And in our galaxy, the Milky Way, billions of stars are capable of having orbiting planets that hold the building blocks of life, a recent study found.

For example, Europa, an icy moon belonging to Jupiter, is probably the greatest object of that kind of speculation.

Beneath the freezing cold surface could well be a massive, liquid collection of water, scientists believe.

That environment might not be so different from the deep frozen lakes of our own polar regions, which we now know to contain intrepid microbes.

Europa is promising enough that Nasa has proposed a mission to check the moon out from a better vantage point.

This icy moon has also taught us that liquid water - and perhaps the early building blocks of life - doesn't require the "prefect" proximity to a nearby sun, which scientists used to believe was necessary to heat up a planet or moon just enough so that water could remain in liquid form.

"We now recognise that habitable zones are not just around stars, they can be around giant planets, too," Jim Green, director of planetary science at Nasa, said. "We are finding out the solar system is really a soggy place."