SETI scans comet 3I ATLAS finds no alien signals
The Allen Telescope Array in Northern California had just finished its seven-hour listen. The 74 million candidate signals were now reduced to nothing. No alien broadcast. No beacon. No message in a bottle from another star. The third interstellar object ever spotted in our solar system, 3I/ATLAS, was just a comet after all.
But the silence itself became the story.
What the Array Heard
The Allen Telescope Array is not a single dish. It is a network of radio antennas spread across the Hat Creek Radio Observatory in Northern California. These dishes work together like a single giant ear, tuned to frequencies that nature never produces on its own.
Sofia Sheikh leads the team at the SETI Institute in California. She and her colleagues pointed this ear at 3I/ATLAS shortly after its discovery. They were hunting for narrowband radio signals — emissions so precise and concentrated that no volcano, no lightning storm, no known cosmic process can create them.
The search found nearly 74 million of these candidate signals. That number sounds huge. But most were trash. Human interference, satellites passing overhead, the comet’s own motion creating false echoes. The team filtered. They sorted. They eliminated.
After all that work, about 200 signals remained mysterious. Then those too were traced back to Earth. Cell towers. Orbiting spacecraft. Radio stations. The final counThe study, accepted for publication in. The Astrophysical Journal, set a hard limitset a hard limit. [3] Any transmitter on or near 3I/ATLAS would have to be weaker than 10 to 110 watts — roughly the power of a household light bulb or a small refrigerator. Nothing stronger exists on that comet.
Three V3I/ATLAS was first seen on April 5, 2024. The ATLAS survey telescope in Chile caught itlescope in Chile** caught it. That telescope is part of the ATLAS project, which normally watches for asteroids that might hit Earth. ATLAS stands for Asteroid Terrestrial-impact Last Alert System. This time it found something that came from outside our neighborhood entirely.
The name 3I/ATLAS tells its story. The “3I” means it is the third confirmed interstellar object ever detected. Before it came 1I/‘Oumuamua in 2017 and 2I/Borisov in 2019.
‘Oumuamua arrived without warning. It tumbled through the inner solar system, elongated and strange. Its shape was unlike any asteroid or comet we had seen. Some scientists wondered if it could be artificial. A lightsail. A probe. A discarded piece of alien technology.
2I/Borisov looked more familiar. It had a coma and a tail — classic comet features. But it came from somewhere else. It carried dust and gas from another star system entirely.
All three objects share one thing. They were born around other stars. Then gravitational kicks — perhaps from passing planets or nearby stars — flung them into the void between the stars. They drifted for millions or billions of years before crossing our path.
What a Comet Tells Us
The new study confirms what astronomers already suspected. 3I/ATLAS is natural. It is a comet, like the ones born in our own solar system, but from a different parent star.
This matters beyond the question of aliens. Every interstellar object is a sample from another solar system. We cannot travel to those distant stars. But sometimes, their debris comes to us.
The comet’s composition, its trajectory, its behavior as it warms near the Sun — all of these are data points. They tell us about the chemistry of other planetary systems. They reveal how common or rare certain materials are across the galaxy.
Astronomers have only seen three of these visitors. Statistically, there should be many more. Some estimates suggest that thousands of interstellar objects pass through our solar system every year. Most are too small and too faint for our telescopes to spot.
The Vera C. Rubin Observatory in Chile, currently under construction, will change that. Its massive camera will scan the entire southern sky every few nights. It is expected to find interstellar objects by the dozens, perhaps by the hundreds.
When that happens, the question will shift. Instead of “Is this one alien?” it will become “What does the population tell us?” Are most interstellar objects comets? Are some asteroids? Do any show signs of technology?
The Technosignature Hunt
The search for extraterrestrial intelligence has evolved. It is no longer just about listening for deliberate messages. The modern approach looks for technosignatures — any sign of technology that leaks into space.
Radio signals are one kind of technosignature. But there are others. Artificial light from cities on distant planets. Industrial pollution in atmospheres. Megastructures that block starlight. Lasers used for propulsion or communication.
The Allen Telescope Array specializes in radio technosignatures. It can scan millions of frequencies simultaneously. It is fast enough to catch brief signValeria Garcia Lopez at Furman University in South Carolina co-authored the new study. (Note: Verify if Garcia Lopez is a co-author — the article does not specify her role in the study, only that she commented.)South Carolina** co-authored the new study. [6] She emphasized that the empty result is not a failure. It is a benchmark.
“The results from 3I/ATLAS show how realistic it is to detect a signal with the technology we have today,” she said. “That is why it is important to keep searching for technosignatures, even from objects we might not expect to have signals.”
The search proved that the equipment works. The filtering methods are sound. The analysis pipeline can handle 74 million signals and reduce them to zero false positives. If a real signal had been there, it would have been found.
The Mirror of Voyager
Sofia Sheikh offered a perspective that reframes the entire search. She pointed to our own spacecraft.
“Eventually, our own Voyager spacecraft will be extraterrestrial artifacts in other stellar systems,” she said. “Given that, it is important that we understand the natural distribution of interstellar objects so that we will be able to identify any anomalies that could one day be signs of an artificial interstellar object.”
Voyager 1 and Voyager 2 left the solar system years ago. They carry golden records with messages from Earth. They are, by any definition, artificial interstellar objects. If another civilization found them, they would know immediately that they were not natural.
But Voyager is tiny. It is dark. It is silent except for a faint radio signal that fades with distance. Finding it would require extraordinary luck and sensitivity.
The same logic applies in reverse. If an alien civilization launched a probe into interstellar space, it would be difficult to detect. It would be small, cold, and quiet. It would not broadcast its presence. It would drift like a rock.
That is why the search for technosignatures must be patient and thorough. Most interstellar objects will be comets. Almost all will be natural. But the one that is not — the one that carries a signal, or shows an unnatural shape, or moves in a way that gravity alone cannot explain — that one will stand out only if we have mapped the natural background first. This systematic approach, as Sheikh noted, is essential for distinguishing anomalies from the ordinary.
The Power of a Light Bulb
The upper limit set by the Allen Telescope Array is revealing. Any transmitter on 3I/ATLAS would have to be weaker than a household appliance. That is not much power.
Consider what it takes to send a signal across interstellar distances. The Voyager spacecraft transmit with about 20 watts of power. But their signals are aimed precisely at Earth. They use large antennas on the ground to receive them. Even so, the signal is incredibly faint by the time it reaches us.
An alien probe would face the same challenge. To be heard across light-years, it would need either a powerful transmitter or a very directional antenna. A weak, omnidirectional signal would be lost in the noise.
The absence of a signal from 3I/ATLAS does not prove it is natural. It only proves that no transmitter stronger than 110 watts is operating on its surface or nearby. A quieter transmitter, or one that was turned off, would remain invisible.
This is the nature of absence. It can constrain possibilities but never eliminate them entirely.
What Comes Next
The search for interstellar objects is just beginning. The next generation of telescopes will find many more. Each one will be a candidate for technosignature searches.
The Allen Telescope Array will continue listening. Other observatories will join the effort. The Breakthrough Listen initiative, based at the University of California, Berkeley, has already committed resources to scanning interstellar objects. [7] The SETI Institute maintains a dedicated team for follow-up observations.
But the real prize is not a single detection. It is the statistical understanding of what is out there. How many interstellar objects pass through the solar system each year? What fraction are comets? What fraction are asteroids? What fraction, if any, show signs of artificial origin?
Answering these questions requires patience. It requires many observations of many objects. It requires ruling out natural explanations before invoking artificial ones.
The silence of 3I/ATLAS is one data point. It joins the silence of ‘Oumuamua and the silence of 2I/Borisov. Together, they form a pattern. So far, every interstellar object we have examined has been natural.
But the sample size is three. That is not enough to draw conclusions about the galaxy. It is only enough to know that the search is possible, the tools work, and the next object could be different.
The Door That Just Opened
The new study closes one question and opens another. We now know that 3I/ATLAS is natural. We have ruled out the most obvious artificial explanations. That is settled.
But the study also demonstrates something more important. It proves that we can detect technosignatures from interstellar objects with current technology. The methods are validated. The pipeline is ready.
The next question is statistical. How many interstellar objects must we examine before we can say, with confidence, that none are artificial? Or, alternatively, how many must we examine before we find the one that is?
This is the door that just opened. It leads from a single observation to a systematic survey. From a curiosity about one comet to a census of everything that passes through our solar system from beyond.
The silence of 3I/ATLAS is not an ending. It is the first measurement in a long experiment. The experiment asks whether we are alone. The answer will come not from one object, but from many. Not from one signal, but from the pattern of silence across the sky.
And when that pattern finally breaks, when a signal appears that cannot be explained away, the Allen Telescope Array will have been ready. The methods will have been tested. The team will know exactly what they are hearing.
That is what the silence of a single comet buys us. It buys us readiness.