(Image credit: Futurism)
In a recent podcast interview, I was asked what makes my scientific work so much fun. I responded that I view science as the privilege to learn, without pretending to know the answer in advance. With a sense of humility, scientists have the privilege of letting evidence rather than popular opinions guide them.
Stories are often crafted in echo chambers controlled by the authority of “experts,” but we can allow nature to educate us about whether these stories are real. To do that, we must contemplate all possible interpretations of anomalous data that does not line up with cherished beliefs.
In this vein, not all objects in the sky must be asteroids or comets. We know that because we launched technological objects to space and some of them, like the Voyager spacecraft, are on their way out of the Solar system. Within a billion years, these spacecraft would constitute interstellar objects that enter planetary systems around stars located 50 thousand light years away, on the opposite side of the Milky-Way disk. At that time, Voyager will be space trash, posing no risk to alien civilizations. But a more advanced civilization with an interstellar agenda might have developed spacecraft that survived interstellar travel and are parked in the outer Solar system.
We have difficulty finding Planet Nine at a distance that is hundreds of times closer to us than the outer boundary of the Solar System. Hence, our telescopes would never be able to detect a fleet of spacecraft based in the outer Oort cloud. However, if a spacecraft dives straight towards the Sun, we might notice it at a distance of a few times the Earth-Sun separation. To avoid being detected, the spacecraft might prefer to approach the inner Solar System from the direction of the Milky-Way center, which is crowded by plenty of background stars. This is the direction from where 3I/ATLAS came from along a path aligned with the orbital plane of the inner planets around the Sun.
Given its speed of 60 kilometers per second, 3I/ATLAS could have started its journey from a parking spot at a thousand times the Earth-Sun separation and arrived at Earth within 80 years from there. This is roughly the period over which radio broadcasting became widespread on Earth, flagging us as a technological civilization and alerting anyone who bothers to eavesdrop on us out there.
The Vera C. Rubin Observatory is expected to discover up to 50 interstellar objects in the coming decade. We must study each and every one of them for the possibility that they might be on a reconnaissance technological mission.
Over the past two weeks since the new interstellar interloper 3I/ATLAS was discovered, I wrote three scientific papers (posted here, here and here) and ten essays (posted here, here, here, here, here, here, here, here, here and here) about this unusual object (in parallel to three other scientific papers on other topics). The bottom line of my work is that if 3I/ATLAS is a comet, then the diameter of its nucleus must be smaller than a kilometer in order for the mass flux of its population to stay within acceptable bounds. However, if its unusually high brightness stems from a solid surface that is 10–20 kilometers in diameter, we should be worried about it possibly representing alien technology.
I laid out this possibility in order to encourage observers who are convinced that 3I/ATLAS is a comet to collect as much data as possible in an attempt to prove me wrong. In the presence of ample data, there will be no leeway for them to shove anomalies under the carpet of conventional thinking. My only fear is of not having sufficient data to infer the true nature of anomalous objects. I am much less fearful of being wrong. Even if 49 out of the next 50 interstellar objects to be discovered by the Rubin Observatory will turn out to be comets or asteroids, the one outlier of technological origin might change the future of humanity.
In case 3I/ATLAS represents a spacecraft of 20-kilometer size, as envisioned by Arthur C. Clark in his novel “Rendezvous with Rama,” we should worry about its intent. At its closest approach to the Sun on October 29, 2025, the stock market might crash if fears from an alien invasion will skyrocket. In that scenario, citizens would lose their trust in governments to protect them. The uncertainty about encountering an invader with a technological advantage would resemble the experience of the Iranian air defense system when the American B-2 bombers arrived at its nuclear sites.
This situation is starkly different from detecting a radio signal from a civilization located thousands of light years away, the primary aim of the SETI community over the past 65 years, since Project Ozma was pioneered by Frank Drake following on the 1959 paper by Phil Morrison and Giuseppe Cocconi. In that case, humanity has plenty of time to contemplate how to respond or worry about a visit from the radio transmitting civilization. However, if an interstellar object is a functional device on a near Earth trajectory, then the visitor is already in our back yard and we have little time to respond.
Our chemical rockets have no way of bridging the velocity gap of 98 kilometers per second between 3I/ATLAS at perihelion and Earth. In addition, 3I/ATLAS will be eclipsed by the Sun at perihelion, making it difficult to detect a maneuver aimed to send smaller objects that will arrive at Earth.
The protocol on how to respond to an alien threat depends on the nature and intent of the associated spacecraft. There is no international organization ready to make a global decision on how to engage with 3I/ATLAS, should it be an alien spacecraft.
The highest priority for us right now is to figure out whether 3I/ATLAS is a sub-kilometer object surrounded by a large dust cloud. If that is not the case, then the anomalies associated with the alignment of its trajectory with the orbital plane of Earth and its close encounter with Venus, Mars, and Jupiter, are alarming.
It would be prudent to establish an alert system regarding interstellar objects in the spirit of the Richter scale for earthquakes. A natural comet would define the zero point whereas a clear detection of a spacecraft, based on the signatures I outlined in a recent essay, would bracket the upper end of the alert scale at a value of ten. Since aliens might not care about the way we split territories on Earth among nations, all humans must cooperate in response to existential threats from space.
“The cat is out of the bag,” as we revealed our technological status through radio broadcasts over the past century. As a result, we should be ready for the possibility of a visitor that detected them. It may come to save us or destroy us. We better be ready for both options and check whether all interstellar objects are rocks.
ABOUT THE AUTHOR
(Image Credit: Chris Michel, National Academy of Sciences, 2023)
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.