This SETI program is chasing down its final 100 signals. Could one of them be from aliens?
The SETI@home Legacy: Chasing Down the Final 100 Signals
As the world's most ambitious citizen science project comes to a close, astronomers are left with a tantalizing question: could one of the final 100 signals detected by SETI@home be from an extraterrestrial civilization?
The SETI@home project, which ran from 1999 to 2020, enlisted the help of millions of users worldwide to analyze data collected by the Arecibo radio telescope in Puerto Rico. The project's sheer scale was unprecedented, with 12 billion candidate narrowband signals spotted over the years. These signals, which appeared as brief blips of energy at a particular frequency coming from a particular point in the sky, were the culmination of a massive effort to scour the skies for signs of intelligent life.
The Birth of SETI@home
In 1999, computer scientist David Anderson and his team at the University of California, Berkeley, launched SETI@home with the ambitious goal of analyzing data from the Arecibo radio telescope. The project's initial success was rapid, with 200,000 users signing up within the first week and 2 million by the end of the year. The data collected by Arecibo was vast, covering billions and billions of stars in the Milky Way.
"We are, without doubt, the most sensitive narrowband search of large portions of the sky, so we had the best chance of finding something," said Eric Korpela, a Berkeley astronomer and co-founder of SETI@home.
The Challenge of Analysis
However, analyzing the data proved to be a daunting task. Until 2016, the team hadn't figured out how to properly scrutinize the vast amount of data they had accumulated. "There's 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," Korpela explained.
To overcome this challenge, the team developed algorithms to spot radio frequency interference (RFI), which reduced the number of signals to be manually inspected. These algorithms, designed to spot RFI, sorted the wheat from the chaff, reducing those 12 billion to 1 million, then 1,000. These 1,000 signals then had to be inspected manually, by eye, before being whittled down to 100 that deserved a second look.
The Role of FAST
The Arecibo radio telescope, where the data for SETI@home was taken, was the world's largest single-dish radio telescope until its collapse in 2020. Today, the Five-hundred-meter Aperture Spherical Telescope (FAST) in China is the only radio telescope capable of taking on these candidate signals. FAST has been patiently following up on the final 100 signals since July 2025.
The Implications of SETI@home
Even if no extraterrestrial signals are found, the SETI@home project has established a new sensitivity level. "If we don't find ET, what we can say is that we have established a new sensitivity level. If there were a signal above a certain power, we would have found it," said Anderson.
The project has also provided valuable insights into the challenges of analyzing large datasets and the importance of crowd-sourced computing power. "We have to do a better job of measuring what we're excluding," Korpela said. "Are we throwing out the baby with the bath water? I don't think we know for most SETI searches and that is really a lesson for SETI searches everywhere."
Forward-Looking Thoughts
As the SETI@home project comes to a close, the question remains: could one of the final 100 signals be from an extraterrestrial civilization? While the answer may remain elusive, the project has provided a valuable legacy for future SETI surveys. "There's still the potential that ET is in that data and we missed it just by a hair," Korpela said.
In the future, a new project could be launched to reanalyze the data using modern crowd-sourced computing power and machine learning. This could provide a new opportunity to uncover signs of intelligent life in the universe. As the search for extraterrestrial intelligence continues, the SETI@home project will remain an important milestone in the history of the field.
