The 3I/ATLAS, neither a spacecraft nor of alien origin: “If we could find other civilizations, it wouldn't be because of comets”

Spectacular hypotheses spread more easily than genuine scientific facts, especially when they come from a respected voice. This has happened with comet 3I/ATLAS —detected last July by the Asteroid Terrestrial-impact Warning System (ATLAS) observatory in Río Hurtado, Chile—which has been the subject of a wave of speculation on social media since Avi Loeb, a Harvard astronomer, suggested it could be an alien spacecraft . For experts, these are nothing more than nonsensical ideas. According to Michael Kueppers, an astrophysicist at the European Space Agency (ESA), what has been observed shows nothing to indicate that it is anything other than a celestial body of interstellar origin; with unusual chemical characteristics, yes, but explainable.

“If we could truly find other civilizations, comets wouldn't be the way to do it,” explains Kueppers, who emphasizes that the unique aspect of 3I/ATLAS lies in its origin: “It's an object that didn't form in our solar system, but elsewhere in the galaxy,” he points out. Although its exact place of origin is unknown, astronomers know that it is an interstellar traveler: a fragment of another planetary system that, after billions of years in space, is now crossing our own.

But what has surprised experts most is its unique composition. Unlike most comets in the solar system—formed primarily of water ice, other ices, and dust— 3I/ATLAS has an unusually high proportion of carbon dioxide (CO₂) relative to water. According to Kueppers, this characteristic could indicate that it formed in a colder environment than its parent system, where volatile elements could accumulate at lower temperatures. However, it could also be due to the effects of its orbit.

Another distinctive feature is its abundance of metallic nickel. While the reason is not yet fully understood, this planetary scientist points out that this finding could provide clues about the diversity of other planetary systems. “These objects allow us to learn firsthand what star systems outside our own are like,” Kueppers explains.

An unusual composition

Unlike the distant, limited images captured by telescopes, interstellar objects like this one bring with them physical material from their ancient worlds (3I/ATLAS is estimated to be probably 3 billion years older than the solar system). So far, only two other such visitors have been detected: 1I/'Oumuamua in 2017 and 2I/Borisov in 2019, each offering another piece of the puzzle about how planets and comets form around other stars.

In his most recent hypothesis, Avi Loeb —a 63-year-old Israeli-American physicist and professor at Harvard University— proposed that the 3I/Atlas would execute a navigation maneuver when it reached its closest point to the center of our planetary system at the end of October (almost 200 million kilometers from Earth) and, being a spacecraft with an alien crew, would release probes towards the planets orbiting the Sun.

Elena Manjavacas, an astronomer at the Space Telescope Science Institute (STScI) in Maryland, dismisses any speculation linking comet 3I/ATLAS to alien technology . For such ideas to have any basis, she points out, extraordinary conditions would have to be met. “First, that life exists elsewhere in the universe; second, that it is intelligent; third, that it has developed a civilization with technological capabilities similar to those of a space agency; and finally, that it knows of Earth's existence and has decided to send a spacecraft here,” the Spanish scientist explains.

According to Manjavacas, the probability of all of that happening simultaneously is practically nil. In contrast, the scientific explanation that it is an interstellar comet is much simpler and coincides with Kueppers's words: 3I/ATLAS has unusual characteristics , but they are consistent with what is expected of an object traveling from cold, distant regions of the galaxy. "It is far more likely that we are seeing a peculiar comet, not an alien spacecraft. That would, in fact, be the least likely possibility of all."

Loeb had previously argued that Oumuamua, with its elongated and somewhat irregular shape, could be an extraterrestrial solar sail or the remains of an artifact created by an alien civilization. He based his hypothesis on the fact that Oumuamua, a fleeting and the first of its kind, lacked a comet's tail and that the data suggested it was unusually bright; he developed these ideas in a popular science book, which was translated into several languages ​​and criticized by the scientific community.

No defense protocol activated

The announcement of an international observation campaign of 3I/ATLAS, promoted by the International Asteroid Warning Network (IAWN) , coincided almost exactly with astronomer Loeb's statements. The overlap of these two news items was enough to unleash a wave of outlandish theories on social media. Some posts even claimed, without any evidence, that NASA had activated a supposed planetary defense protocol in anticipation of the interstellar object's visit.

The campaign—scheduled to run from November 27 to January 27—is a routine scientific initiative designed to study objects with unusual trajectories or compositions. According to the IAWN, a UN-coordinated network of space agencies and observatories worldwide, the goal is to improve the accuracy of calculations regarding the comet's position, speed, and chemical composition. It is not a defensive maneuver, but rather an opportunity to deepen our understanding of a unique visitor.

“The first thing is to listen to the scientists,” says Manjavacas. “We base our opinions on evidence, not wishful thinking. The idea that an intelligent civilization sent a spacecraft here might sound appealing, but it’s infinitely improbable.” Even so, he welcomes the interest the phenomenon is generating. “The important thing is that astronomy continues to fascinate people. Not because of extraterrestrials, but because it helps us understand our place in the universe.”