When the first alien life is discovered, it will not be on a planet

Physicist Stephen Hawking and Russian billionaire Yuri Milner are teaming up with a host of other physics and cosmology luminaries to plan a mission to Alpha Centauri, a star far beyond our own solar system that will take at least two decades to reach.

They hope to send miniature robots, the size of iPhones, to explore the faraway depths of the Milky Way and search for signs of life.

The project, dubbed Breakthrough Starshot, was made public on April 12.

At the official announcement, the physicist and mathematician Freeman Dyson told the assembled crowd that while Starshot's destination would be Alpha Centauri, what these robots find along the way may be even more interesting.

"The space between here and Alpha Centauri is not empty ... there are thousands of objects in between," he said. "We know that there are billions of planets ... but we also know that there are trillions of comets and asteroids."

And he predicts that our focus on planets may have obscured something truly exciting: Some of these smaller objects might be teeming with life.

"I've always believed that planets are not the big thing," he said. "I've made a bet that when the first alien life is discovered, it will not be on a planet."

This idea is not entirely new. Scientists recently claimed that there was evidence of alien life on the comet Philae, but those claims turned out to be unfounded.

Still, it's entirely possible that life on Earth originated thanks to meteors that pummeled our planet with the elements required for life. If that's the case, there's no reason to believe that similar bodies are not still out there. A theory called panspermia suggests that it's comets and asteroids that spread the building blocks for life all around the universe.

If the Starshot initiative is able to get off the ground, it may not tell us anything for certain about the origins of life on our own planet. But it could provide tantalizing clues about whether alien life is hiding on fiery rocks hurtling through the sky.