On a chilly morning last week, Jill Tarter sat in a makeshift corner office facing the Allen Telescope Array, pondering a set of parallel lines that striped a window in her MacBook.

Tarter directs the Centre for SETI Research - SETI is the search for extraterrestrial intelligence - and the 42 antennas that sit outside her window are once again sampling radio emissions from a patch of sky that offers a window into one of the spiral arms of our galaxy. Shuttered for more than a year by budget problems, the array was turned back on in December to continue its search. Now, the searchers have another reason for optimism.

With new web-based software called SETILive, an army of independent citizenscientists are being enlisted to help with the hunt for unusual signals. The software, which can be found at Setilive. org, was designed by Zooniverse, a team of programmers and scientists who have created webbased systems to enable citizen participation in research in fields like astronomy and marine biology. SETILive was switched on late last month.

In two weeks, more than 40, 000 volunteers have signed up, and more than one million radio samples have been analysed. Thanks to the remarkable revelations of the Kepler satellite mission, the searchers have a target list. Kepler has revealed thousands of planets relatively close to our solar system. Now, rather than sweeping the entire sky, the array of 42 antennas, spread over the countryside in the mountain valley here in Northern California, dart electronically from target to target, capturing snippets of what the watchers hope might be evidence of alien life.

Tarter, a 68-year-old astronomer, said the use of volunteers was an experiment. She is hoping that the SETI researchers can use human pattern recognition to fine-tune software algorithms that in the past have been used to look for tantalising signals hidden among fields of natural stellar radiation and human-made sources of interference.

"We have software that finds narrow-band signals much better than your eye can, " Tarter said. "What we're doing with humans is to see how well they do. We are giving them marking tools and learning how they extract features. "
In the past, she said, a huge challenge for the SETI researchers has been that the researchers have had to contend with powerful interference sources at the sites of their radio observatories from both Earth-based radars and satellite communications. The Allen telescope site in Hat Creek is relatively free from interference sources.

There is also, of course, the "drunk under the streetlight" effect. SETI researchers have devoted much of their resources to the electromagnetic spectrum from 1 to 10 gigahertz because it offers a relatively quiet window for observation from within the Earth's atmosphere. If there were an alien civilisation orbiting a nearby star, no one is really certain how they would communicate with us. Radio or television broadcasts are a possibility, but so are powerful pulsed lasers and conceivably communications that employ some advanced phenomenon like quantum entanglement.

For the moment, however, SETILive is adding a new, and already occasionally unpredictable, dimension to the hunt for alien worlds. NYT