© NASA
Enceladus
Speaking at a Seattle conference, 'A New Space Age', Milner said his science team believes there are three potential locations for extra-terrestrial lifeforms in our solar system: under the surface of Mars, Jupiter's moon Europa, and "the most promising candidate," Enceladus.

Located 1.27 billion miles away from Earth, Enceladus has a surface temperature below -200 Celsius, but is thought to harbor a giant hot sub-surface ocean that shoots up plumes of material hundreds of miles up.

"We formed a little workshop around this idea: Can we design a low-cost, privately funded mission to Enceladus which can be launched relatively soon, and that can look more thoroughly at those plumes, try to see what's going on there?" Milner outlined.

He said the chemical makeup of the water vapor, ejected out of geysers on the surface, could provide a "a smoking gun for life below the surface." He tempered expectations, though, by saying he expects to find "not intelligent life, maybe microbial life, or something more serious."

Much of the knowledge about the 500-km diameter Enceladus comes from the recently-ended NASA Cassini mission, which provided highly-detailed photographs of the moon during its fly-bys.

But Milner, whose net worth is estimated at $3.5 billion, said he plans to send his probe - whose exact form and route have not yet been established - "ahead of a more expensive mission from NASA that might take ten years to launch."

The billionaire, who trained as a physicist in Soviet Russia, and currently splits his time between California and Moscow, said that if successful, the expedition would become "the first-ever privately-funded interplanetary science mission."

Fellow billionaire Elon Musk and Jeff Bezos are also developing their own space ventures, though both have been more concerned with orbital and Mars travel.