A Russian billionaire is bankrolling a $100 million effort to scan the cosmos for evidence of alien life, with a bonus $1 million contest to decide what to say to them.

Alongside renowned physicist Stephen Hawking, technology investor Yuri Milner announced Monday that he will fund Breakthrough Listen — a project scientists are calling the most comprehensive attempt so far to detect signals from extraterrestrials

Milner's investment will buy time on two of the planet's most powerful and sensitive radio telescopes, and will pay for sophisticated receivers that can scan billions of radio frequencies simultaneously. Over 10 years, the project will focus on the million stars closest to Earth, as well as a hundred nearby galaxies. According to a press release, it will survey 10 times more of the sky, cover five time more of the radio spectrum and work a hundred times faster than any previous program.

Milner said the effort will produce as much data in a day as any other attempt has in a year, and all of it will be available to the public.

"More data will be open than ever in the history of science," said Milner, adding that he is banking on the "Silicon Valley approach" that uses social networks and crowdsourcing.

Hawking was also at the Royal Society, in London, to lend his support. Whatever the answer, he said, "there's no bigger question" than whether we're alone.

"In an infinite universe, there must be other occurrences of life," he said. "Or do our lights wander a lifeless cosmos — unseen beacons, announcing that here, on one rock, the universe discovered its existence? Either way … It's time to commit to finding the answer."

But Hawking warned that we should be cautious if we do find anyone. From their lofty heights, sophisticated aliens might view us as worthless, he said, suggesting that they may have few ethical qualms about eradicating or colonizing us. Since we know nothing about alien ideologies, our only guide is the bloody record of human history.

"If you look at history," he said, "encounters between civilizations with advanced and primitive technologies have gone badly for the less advanced. A civilization reading one of our messages could be billions of years ahead. If so, they will be vastly more powerful and may not see us as any more valuable than we see bacteria."

If we do choose to communicate, it wouldn't be the first time. The Voyager spacecrafts, launched in the 1970s, carry golden records with messages from Earth, including a speech by US President Jimmy Carter and whale sounds. Carl Sagan's widow, Ann Druyan, helped lead that project, and even had her brain waves included on a record. Monday, she was with Hawking and Milner to present a $1 million contest that will select the best messages to send back to anyone we find, though there's no guarantee the project will actually transmit the winner across the void.

According to Druyan, the point is to have a debate about how we want to represent ourselves as a species.

"It's a great way to develop a degree of self-awareness of what it is to be human," she said.

Participants would also be free to debate whether we should establish contact at all.

The other scientists on the panel weren't quite as worried about a looming alien apocalypse. They said circumstances were finally coming together for a breakthrough. Frank Drake, one of the pioneers of the Search for Extraterrestrial Intelligence (SETI) project, was relieved to finally have a wealthy patron to help break decades of neglect.

"For once, after years of being guest observers, and poverty stricken, we will finally have stable funding so we can plan from one year to the next," he said. "We can hire talented people, and we will have the most powerful and enduring search that has ever been launched."

The scientists also said that recent discoveries have raised the probability of success. Lord Martin Rees, Baron of Ludlow and Britain's Astronomer Royal, said that technology now "allows for more sensitive searches than could be done before" and praised the "global reach" provided by citizen science and social media.

Geoffrey Marcy, a Berkeley University Astronomer who's discovered more extraterrestrial planets than anyone else, said there's now substantial evidence that at least 10 percent of the stars in our own galaxy have planets with conditions that could support life. There could be billions of Earth-like worlds in the Milky Way alone.

"I would bet my house that among the nearest 100 star systems, single celled organisms can be found and are fluorescing," he said. "Or at least I'd bet Yuri's house."

The more difficult question, the scientists said, is whether that life has evolved to the point where it could communicate with us. Even if it had, there's no guarantee it would survive for long.

Hawking put it in characteristically bleak language.

"We only need to look in the mirror to know that [intelligent life] can be very fragile and self-destructive."