EarthSky\u2019s 2026 lunar calendar shows the moon phase for every day of the year. Available now. Get yours today!<\/p>\n
- \n
- UC Berkeley\u2019s SETI@home project<\/strong> was one of the most popular crowd-sourced research projects ever. For 21 years, people used their home computers to look for curious signals from space. <\/li>\n
- The project turned up some 12 billion signals<\/strong> of interest. Scientists winnowed those signals down to a million candidates, and then finally to 100 that were worth another look.<\/li>\n
- Now, scientists are taking a second look,<\/strong> searching for the signals again with observatories such as China\u2019s Five-hundred-meter Aperture Spherical Telescope.<\/li>\n<\/ul>\n
The University of California at Berkeley published this original story on January 12, 2026. Edits by EarthSky.<\/p>\n
SETI@home is taking another look at 100 notable signals<\/h3>\n
For 21 years, between 1999 and 2020, millions of people worldwide loaned UC Berkeley scientists their computers to search for signs of advanced civilizations in our galaxy.<\/p>\n
The project \u2013 called SETI@home, after the Search for Extraterrestrial Intelligence (SETI) \u2013 generated a loyal following eager to participate in one of the most popular crowd-sourced projects in the early days of the internet. They downloaded the SETI@home software to their home computers and allowed it to analyze data recorded at the now-defunct Arecibo Observatory in Puerto Rico to find unusual radio signals from space. All told, these computations produced 12 billion detections or, as computer scientist and project co-founder David Anderson said: <\/p>\n
\n
\u2026 momentary blips of energy at a particular frequency coming from a particular point in the sky.<\/p>\n<\/blockquote>\n
After 10 years of work, the SETI@home team has now finished analyzing those detections, winnowing them down to about a million candidate signals and then to 100 that are worth a second look. They have been pointing China\u2019s Five-hundred-meter Aperture Spherical Telescope (FAST) at these targets since July, hoping to see the signals again.<\/p>\n
Learning from results and moving forward<\/h3>\n
Though astronomers have not yet analyzed the FAST data, Anderson admits he doesn\u2019t expect to find a signal from ET. But the results of the SETI@home project \u2013 presented in two papers published last year in The Astronomical Journal<\/em> \u2013 provide lessons for future searches and point to potential flaws in ongoing searches.<\/p>\n
Anderson said: <\/p>\n
\n
If we don\u2019t find ET, what we can say is that we established a new sensitivity level. If there were a signal above a certain power, we would have found it. Some of our conclusions are that the project didn\u2019t completely work the way we thought it was going to. And we have a long list of things that we would have done differently and that future sky survey projects should do differently.<\/p>\n<\/blockquote>\n
Sifting through billions of signals from future searches<\/h3>\n
According to astronomer and SETI@home project director Eric Korpela, searches like SETI@home will inevitably turn up billions of possible signals. The challenge for researchers is to develop algorithms to cull the spurious signals caused by noise or radio interference without eliminating actual beacons from a distant civilization. Radio frequency interference, or RFI, comes not only from satellites orbiting Earth and scattered throughout the solar system, but from radio and TV broadcasts and even microwave ovens. Korpela said:<\/p>\n
\n
There\u2019s no way that you can do a full investigation of every possible signal that you detect, because doing that still requires a person and eyeballs. We have to do a better job of measuring what we\u2019re excluding. Are we throwing out the baby with the bath water? I don\u2019t think we know for most SETI searches, and that is really a lesson for SETI searches everywhere.<\/p>\n<\/blockquote>\n
Testing with fake signals<\/h3>\n
Anderson and Korpela addressed that issue by inserting some 3,000 fake signals \u2013 called birdies \u2013 into their data pipeline before combing through it to eliminate the RFI and noise. They blinded themselves to the nature of these fake signals, and calculated their sensitivity based on the signal power of the birdies they were able to detect.<\/p>\n
Korpela pointed out that nearly all searches today assume a civilization would put lots of power into a narrow frequency band to get the attention of other civilizations, then send information or data through an adjacent broadband frequency. To increase the chances of being detected, the beacon should be around a frequency which astronomers use to observe the universe, Korpela said. The most likely frequency is around the radio wavelength of 21 centimeters, which astronomers use to map hydrogen gas in the galaxy. Korpela said:<\/p>\n
\n
This powerful narrow-band beacon would be something that\u2019s easy to detect. Then, once someone had detected that, they would dedicate more observing to try and find signals near it in frequency that might be lower power and wider band that contain information. If we saw an extraterrestrial narrowband signal somewhere, we would probably have every telescope, radio telescope and optical telescope available pointing at that point on the sky, searching in all frequencies for anything else. So far we haven\u2019t had that. If we had, I think we would all know about it.<\/p>\n<\/blockquote>\n
More than a million volunteers<\/h3>\n
Despite its failure to find ET, was SETI@home a success?<\/p>\n
Anderson said:<\/p>\n
\n
I\u2019d say it went way, way, way beyond our initial expectations. When we were designing SETI@home, we tried to decide whether it was worth doing, whether we\u2019d get enough computing power to actually do new science. Our calculations were based on getting 50,000 volunteers. Pretty quickly, we had a million volunteers. It was kind of cool, and I would like to let that community and the world know that we actually did some science.<\/p>\n<\/blockquote>\n
![\"Four](\"https:\/\/earthsky.org\/upl\/2026\/01\/SETIteam-UC-Berkeley.jpg\")
An early photo of some of the SETI@home team, with David Anderson seated in the front. Standing, left to right, are Jeff Cobb, Matt Lebofsky, Eric Korpela and Dan Werthimer. Image via SETI@home\/ UC Berkeley.<\/figcaption><\/figure>\n Distributed computing<\/h3>\n
When Anderson first began working on SETI@home in the mid-1990s, he taught computer science at UC Berkeley and conducted research in distributed computing. That\u2019s breaking down large and complex problems into chunks that could be handled by smaller computers. This was a workaround for people who didn\u2019t have access to a supercomputer.<\/p>\n
A UC Berkeley computer science graduate and former student of Anderson\u2019s, David Gedye, suggested that the growing network of home computers could be tapped through distributed computing to analyze signals from radio telescopes in search of unusual patterns produced by an advanced civilization. It\u2019s what\u2019s known today as a technosignature.<\/p>\n
The launch of SETI@home<\/h3>\n
Anderson subsequently teamed up with Korpela and UC Berkeley electrical engineer and astronomer Dan Werthimer. Together, they launched SETI@home in 1999. Within days, 200,000 people from more than 100 countries had downloaded the software. A year later, it had 2 million users.<\/p>\n
The data came from the 300-meter Arecibo radio telescope. The researchers recorded it passively as other astronomers pointed the radio dish \u2013 at the time, the world\u2019s largest \u2013 at different regions of the sky for study. This so-called commensal observing turned out to be very effective. Over the course of the project, the astronomers observed each area of the sky visible from Puerto Rico \u2013 a third of the entire sky \u2013 12 or more times, with some areas observed hundreds or even thousands of times. Anderson said:<\/p>\n
\n
From Arecibo we covered most of the stars in the Milky Way, which is billions and billions.<\/p>\n<\/blockquote>\n
Korpela added:<\/p>\n
\n
We are, without doubt, the most sensitive narrow-band search of large portions of the sky, so we had the best chance of finding something. So yeah, there\u2019s a little disappointment that we didn\u2019t see anything.<\/p>\n<\/blockquote>\n
All-sky scans versus targeted searches<\/h3>\n
Most current SETI searches \u2013 including the 10-year-old Breakthrough Listen project \u2013 are targeted searches rather than all-sky scans. That is, they look for technosignatures from specific nearby stars or more distant stars that have been found to harbor planets. The radio telescopes used, such as the Greenbank Telescope in West Virginia and the MeerKAT array in South Africa, are still only capable of detecting an Arecibo-sized transmitter relatively nearby, in galactic terms. Korpela said:<\/p>\n
\n
In order to probe farther distances, you need bigger telescopes and longer observing times. It\u2019s always best if you are able to control the telescope for your project. We weren\u2019t able to control what the telescope was doing.<\/p>\n<\/blockquote>\n
The final analysis<\/h3>\n
The software that Korpela developed for SETI@home took the radio data from Arecibo \u2013 frequency, intensity, position in the sky \u2013 and manipulated it mathematically in a process called a discrete Fourier transform. This breaks the frequencies into little bins. Since Earth is moving, as is any likely signal source, the software scanned the observations for frequency shifts, called Doppler drift. Anderson said:<\/p>\n
\n
We actually had to look at a whole range of possible drift rates \u2013 tens of thousands \u2013 just to make sure that we got all possibilities. That multiplies the amount of computing power we need by 10,000. The fact that we had a million home computers available to us let us do that. No other radio SETI project has been able to do that.<\/p>\n<\/blockquote>\n
The 12 billion interesting signals these home computers identified had to be vetted, however, and Anderson admits that in the early years of SETI@home, they had not thought much about how to do that:<\/p>\n
\n
Until about 2016, we didn\u2019t really know what we were going to do with these detections that we\u2019d accumulated. We hadn\u2019t figured out how to do the whole second part of the analysis.<\/p>\n<\/blockquote>\n
Analzying the SETI@home data<\/h3>\n
The winnowing required a computing cluster with a large amount of storage and memory, which the Max Planck Institute for Gravitational Physics in Hanover, Germany provided. The supercomputer allowed Anderson and Korpela to eliminate RFI and noise, reducing the billions of detections to a couple of million signal candidates. As Anderson said: <\/p>\n
\n
\u2026 sets of detections that come from more or less the same place in the sky and at more or less the same frequency but possibly a lot of them spread out over time. <\/p>\n<\/blockquote>\n
Once they had ranked these by likelihood of being real, the top thousand had to be reviewed manually. Korpela and Werthimer worked to review the candidates and narrow the field to about 100. These are being targeted by FAST, each spot on the sky recorded for about 15 minutes. FAST has about eight times the collecting area of Arecibo.<\/p>\n
The final analysis of these signals is yet to come, Anderson said, but: <\/p>\n
\n
\u2026 these two papers are the important conclusions of SETI@home.<\/p>\n<\/blockquote>\n
Is a similar crowdsourced SETI project feasible today?<\/h3>\n
Korpela thinks the answer is yes. The FAST telescope is already conducting a commensal survey. That data could be chunked and distributed to citizen scientists for analysis. Home computers could process this data on a platform for volunteer computing called BOINC, which Anderson created and continues to develop.<\/p>\n
BOINC, funded by the National Science Foundation, is currently used by several crowd-sourced computing projects, including Rosetta@home, which calculates how proteins fold in 3D; Einstein@home, which analyzes data in search of pulsars; and LHC@home, which simulates particle collisions at CERN\u2019s Large Hadron Collider. Faster computers and faster internet speeds could allow analysis of much larger chunks of data than could SETI@home, which started during the era of slow, dial-up modems that made it laborious to download large amounts of data. Korpela said:<\/p>\n
\n
I think it still captures people\u2019s imagination to look for extraterrestrial intelligence. I think that you could still get significantly more processing power than we used for SETI@home and process more data because of a wider internet bandwidth. The biggest issue with such a project is that it requires personnel, and personnel means salaries. It\u2019s not the cheapest way to do SETI.<\/p>\n<\/blockquote>\n
What remains of SETI@home?<\/h3>\n
Six people once operated SETI@home, but Korpela is the only paid staff member now, and he is semi-retired. But he sees crowd-sourced computing as an opportunity to better analyze SETI radio data using lessons from SETI@home. That could include a second look at all the SETI@home data. Korpela said:<\/p>\n
\n
In a world where I had the money, I would reanalyze it the right way, meaning I\u2019d fix the mistakes that we made. And we did make some mistakes. These were conscious choices because of how fast computers were in 1999. There\u2019s still the potential that ET is in that data and we missed it just by a hair.<\/p>\n<\/blockquote>\n
Bottom line: The SETI@home project is taking a second look at 100 notable signals. Researchers are using China\u2019s FAST radio telescope to gather data and prepare for future surveys.<\/p>\n
Via UC Berkeley<\/p>\n<\/div>\n
- The project turned up some 12 billion signals<\/strong> of interest. Scientists winnowed those signals down to a million candidates, and then finally to 100 that were worth another look.<\/li>\n