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How SETI@home accelerated alien hunting with an army of armchair astronomers

On July 23, 1995, Alan Hale and Thomas Bopp both had telescopes trained on the sky. Both noticed a fuzzy object that turned out to be a comet. Hale has a PhD in astronomy, but Bopp was borrowing a friend’s instrument. Because they’d spotted the object at about the same time, Hale and Bopp both had their names attached to the now famous comet.

There’s always been plenty of space for amateurs in the field of astronomy. While it’s often been solo star hunters or small societies, the SETI@Home experiment brought together millions of citizen scientists interested in learning if humans are alone in the universe.

If you dropped by a dorm room in the early 2000s, you might have seen — in place of an ocean- or space-themed screensaver — an idle computer displaying a colorful 3D graph along with information about CPU time and other data. That was all thanks to SETI — the Search for Extraterrestrial Intelligence. For almost 21 years, the organization’s distributed citizen science project, SETI@home, has been utilizing enthusiasts’ computers to analyze radio telescope data in the hopes of finding signals sent by extraterrestrial life.

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Event Horizon Telescope

In search of a signal

“A long-standing problem in trying to find extraterrestrial intelligence is that we can always collect more data from the telescopes than we can analyze with the instruments that we have there,” Eric Korpela, the current director of SETI@home, told Digital Trends.

Visualizing SETI@home

David Gedye, a graduate student at the University of California, Berkeley in the mid-1990s, came up the original idea for the project. “He figured that if we could get 10,000 people to donate their computer time, we could do a much better job of analyzing data,” said Korpela. The experiment launched in May 1999. Within the first week, nearly 300,000 computers were processing data from the Arecibo Observatory. After a couple of months, there were over a million.

Searching for extraterrestrial intelligence involves looking at a spot in the sky and seeing a signal. Look again several months later, and it’s still there, in the same spot. For your signal to rise above the background noise, you either compress it into a narrow frequency band or compress it in time,” said Korpela. The signal might be a single, long tone, like a whistle, or come in pulses. If the extraterrestrials are on a planet, then the signal will get blocked as it rotates. “You have to take into account that half the time the signals are going to be visible, and you have to account for the orbital and the rotational motions of that planet,” he said. On top of all that, there’s interference from Earthling-made objects, like satellites and cell phones.

Modem home

“In 1999 when we started, we sized our data chunks that we were sending to people to be about the size that you could do in a reasonable amount of time on a home computer — a reasonable amount of time being a week,” said Korpela. At the time, it would take about five minutes to download the 350 KB of data — important for the dial-up modems of the time. These data chunks or work units are still the same size, but now they take virtually no time to download. Processing is much quicker, too. What once took a week, a modern computer can do in about an hour and a half.


Because the SETI@home team wasn’t prepared for the early levels of interest, the system initially crashed with the influx of people. During a 2009 talk, Dan Werthimer, one of the project’s co-founders, said it had attracted 5.46 million participants, in 226 countries, which equalled 2.3 million years of computing time. With such a long-term project, interest has waxed and waned over the years, with news about SETI bringing newcomers. “For the last few years, we’ve been averaging around 150,000 people,” said Korpela. Most of them run the application on a couple of computers or an Android device. Current smartphones are more than capable of running a program built for late-’90s computers. However, Korpela admits phone tech is outpacing their ability to keep up, and the Android app is a bit out-of-date. With limited funding, it’s hard to divert resources. The team relies on its volunteers to let them know when there’s a glitch with the software.

No signs yet

As the tech has changed, the SETI@home project has evolved as well. It’s analyzing some of the data from the Berkeley SETI Research Center’s Breakthrough Listen project, which is looking for signals with the Green Banks and Parkes telescopes. It’s also expanded the types of signals it’s looking at, from narrowband to wideband, as well. With wideband, SETI@home is searching for frequencies with more data capacity.

“Over the last 20 years, we’ve gotten billions and billions of potential signals,” said Korpela. “I think at last count, it was close to 20 billion potential signals in our database.” He and the team are working on software to analyze all that information. In some upcoming papers, the team will list the most promising areas of the sky. The software injects signals that the SETI@home team believes mimics what an E.T. would send. Thus far, it hasn’t found anything that resembles this artificial extraterrestrial intelligence. If anything looks interesting, Korpela hopes others might take a look. China’s new FAST Radio Telescope is one of the world’s most powerful. “Maybe if you point a bigger telescope at it, maybe it is interesting,” Korpela said of some of the potential spots. “So that sort of thing might raise the interest of more people, I think.”

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