It's a question only the likes of Russian billionaire Yuri Milner ever have to ask themselves, and his answer is simple: alien hunting. Together with Stephen Hawking and Mark Zuckerberg, Milner has launched a $100 million mission to go searching for aliens in outer space - specifically, to a star system 25 trillion miles (and 4.37 light years) from Earth called Alpha Centauri.

The plan? To send a fleet of 'nanocraft' propelled by beams of light from Earth to the distant star system, with the aim of reaching it 20 years from launch. It would take the fastest spacecraft currently available a staggering 30,000 years to get there, hence the $100 million required for an out-of-this-world research and engineering program to develop the nano-fleet.

Hawking, Zuckerberg and Milner have secured the former director of NASA's Ames Research Centre Pete Worden to lead the mission, dubbed Breakthrough Starshot. It's being labelled the most ambitious alien-hunting mission ever attempted, and follows Hawking's highly publicised assertions that humankind must look to colonise outer space for its survival.

"Earth is a wonderful place, but it might not last forever," he says. "Sooner or later, we must look to the stars. With light beams, light sails and the lightest spacecraft ever built, we can launch a mission to Alpha Centauri within a generation."

Stephen Hawking, Mark Zuckerberg and a Russian billionaire... what could go wrong?