Hunt for Extraterrestrial Life Gets New Weapons and Focus

Scientists are ramping up the search for extraterrestrial life with a powerful array of new telescopes and a refined sense of where to look within the vast expanses of the universe.

At the annual conference of the American Assn. for the Advancement of Science last month, a panel of experts discussed the key components of life and what it might mean to find them within our solar system -- or beyond.

Even in the absence of a breakthrough, Nathalie Cabrol of the SETI Institute in Mountain View, Calif., said such efforts could pay dividends for thinking about life on an ever-changing Earth.

“It is the way we are going to understand where we are coming from and how we are going to survive as a species,” she said.

Although NASA’s Spirit and Opportunity rovers continue trundling across Mars and gathering evidence that the Red Planet once harbored water, SETI (Search for Extraterrestrial Intelligence) is the only research program looking for life beyond the solar system.

Jill Tartar, who heads the Center for SETI Research at the nonprofit institute, put the enormity of the challenge into perspective: 100 billion galaxies are believed to exist, each with 100 billion stars.

So where to begin?

Margaret Turnbull of the Carnegie Institution of Washington has helped to whittle down a preliminary list of about 120,000 stars.

Among her considerations, Turnbull said, is that a star’s solar system should include a “habitable zone” that allows liquid water. Also, a star more than 1.5 times the size of our sun likely wouldn’t live long enough to allow advanced life, and stars younger than 3 billion years probably wouldn’t have allowed enough time for advanced life forms to establish themselves.

After scrutinizing all the candidates, Turnbull ended up with a list of 17,129 stars.

“So we’ve got our work cut out for us,” she said.

To aid in the search, SETI is setting up the Allen Telescope Array, a joint project with the Radio Astronomy Laboratory at UC Berkeley.

The cluster of 350 radio antennas, scheduled for completion in June 2008, will allow astronomers to look for new planets or listen for radio transmissions sent from civilizations in other solar systems.

Tartar said previous technologies allowed researchers to scan about 1,000 stars over a decade. With the Allen Telescope Array, funded largely by Seattle billionaire Paul Allen, SETI scientists believe they will be able to search at least 1 million stars in the coming decade.

Searches for far smaller signs of life are ongoing as well.

Pascale Ehrenfreund of the Leiden Institute of Chemistry in the Netherlands said scientists had identified about 140 kinds of molecules in space -- two-thirds of which include carbon, the common denominator of life on Earth. Carbon chemistry in the universe seems to follow the same pathways, she said, leading many scientists to suggest a carbon-focused search for identifying other life forms.

SETI’s Tartar predicted the overall search could yield headlines within a few decades, “but we won’t know if we’ve found microbes or mathematicians.”