By Sarah McBride and Ben Hirschler

SAN FRANCISCO/LONDON (Reuters) - Scientists are about to embark on the biggest search yet for alien life, sweeping the skies for signals of civilizations beyond our solar system with $100 million from a Russian billionaire and the backing of physicist Stephen Hawking.

Whether we are alone in the universe has engaged minds down the ages, and the recent discovery that there may be tens of billions of habitable planets in our galaxy alone has added urgency to finding an answer.

"There is no bigger question. It’s time to commit to finding the answer - to search for life beyond Earth," Hawking told reporters at the program's launch in London on Monday.

Some of the world's largest radio telescopes will be used to scan for distinctive radio signals that could indicate the existence of intelligent life.

Astronomers will listen to signals from the million star systems nearest to Earth and the 100 closest galaxies, although they do not yet plan to send messages back into space.

Hawking said some form of simple life on other worlds seemed very likely, but the existence of intelligence was another matter, and humankind needed to think hard about making contact.

"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," he said.

The 10-year project, dubbed Breakthrough Listen, is funded by Russian Internet entrepreneur Yuri Milner, himself a physicist by training, who made his fortune from savvy early investments in startups such as Facebook Inc.

He said he aimed to bring a Silicon Valley approach to "the most interesting technological question of our day".

Milner became fascinated by the notion of extraterrestrial life after reading astrophysicist Carl Sagan's "Intelligent Life in the Universe" as a 10-year-old in Moscow.

He believes other civilizations could teach us how to handle challenges such as allocating natural resources, he said in an interview. And if we don't find them, we can learn other lessons.

"If we're alone, we need to cherish what we have," he said. "The message is, the universe has no backup."

The new project dwarfs anything else in the field, known by the acronym SETI for the "search for extraterrestrial intelligence". Globally, less than $2 million annually is spent on SETI, said Dan Werthimer, an adviser to Milner's project who directs the SETI@home program affiliated with the University of California in Berkeley, which asks volunteers to run software on their home computers to analyze data.


Today, due to technology improvements, including in computing power and telescope sensitivity, $100 million will go much farther than in the early 1990s, the last time SETI had significant funding.

The advances allow scientists to monitor several billion radio frequencies at a time, instead of several million, and to search 10 times more sky than in the early 1990s.

Any signals the scientists detect will have been created years ago, perhaps even centuries or millennia earlier. Radio signals take four years simply to travel between Earth and the nearest star outside our solar system.

Breakthrough Listen will book time at radio telescopes, including at Australia's Parkes Observatory in New South Wales and the Radio Astronomy Observatory in Green Bank, West Virginia. Milner plans to book about two months a year at each site, a boon to scientists who normally might get two days a year on the telescopes.

The team, led by scientists such as Peter Worden, who until earlier this year directed the NASA Ames Research Center, will organize the radio signals they find, make the data public, and examine it for patterns.

The goal lies less in understanding the signals than in establishing whether they were created by intelligent life rather than natural phenomena.

Scientists say the fact that humans have developed radio signaling makes it a good bet that others may use it as well.

"It doesn't tell you anything about the civilization, but it tells you a civilization is there," said Frank Drake, another of the project's supporters.

Drake, together with Sagan, sent the first physical message into space in 1972, the Pioneer plaques on board the Pioneer 10 U.S. spacecraft.

In addition to checking for radio signals, Breakthrough Listen will hunt for light signals using a telescope at the Lick Observatory in California.

(Editing by Stephen R. Trousdale, Richard Chang and Peter Graff)