What is the Loeb Scale, and how is 3I/ATLAS rated on it by the Harvard physicist?

Harvard physicist Avi Loeb has drawn attention for his take on the interstellar object 3I/ATLAS, which was officially observed on July 1, 2025.

According to NASA, “comet” 3I/ATLAS is the “third known object from outside our solar system to be discovered passing through our celestial neighborhood.”

However, Loeb has refrained from issuing a conclusive identity to the object. While he has entertained the possibility of 3I/ATLAS being a natural comet, he has also emphasized its potential as extraterrestrial technology. 

While NASA and some other scientists classified 3I/ATLAS as a comet, Loeb remains open-minded due to anomalies in the interstellar object that have been observed or deduced through research.

These anomalies make 3I/ATLAS stand out from the usual characteristics of comets. 

With that in mind, Loeb formulated the Loeb Scale in a paper he co-authored with Omer Eldadi and Gershon Tenenbaum. 

“The Loeb Scale serves as a tool for ranking interstellar artifacts along a continuum ranging from ordinary natural bodies (Level 0) to confirmed technological artifacts that potentially pose a risk to humanity (Levels 8–10),” the description read. 

In other words, the scale was a classification system used to evaluate the interstellar objects based on the level of anomalies they exhibit. 

While discussing the unusual nature of 3I/ATLAS, Loeb rated it with the rank of 4 on the Loeb Scale. 

More details on the different classes on the Loeb Scale and the anomalies in 3I/ATLAS

In a Medium blog post, Loeb wrote in September 2025, he refined the Loeb Scale by assigning “observable features of ISOs” with a rank. 

The ranking system begins at Level 0, which corresponds to a natural interstellar object whose properties are identical to those of known comets or asteroids. 2I/Borisov is one such comet that falls under this category. 

At Level 1 came “objects with minor deviations or inconclusive data that do not strongly challenge a natural interpretation.”

Level 2 includes ISOs, which showcase “some unusual properties.” However, they still do not give rise to speculations about their natural origins. 

Level 3 is the mark on the Loeb Scale, in which researchers study the object with a curious approach.  

It is where “persistent anomalies appear, with features such as repeated but unexplained variations in trajectory or unusual albedo or morphology.”

But even then, according to Loeb, it does not trigger significant discussion about the possibility of an artificial origin. 

Level 4, where Loeb ranks the interstellar object 3I/ATLAS, is the “critical threshold,” where the anomalies are considerable to suggest a technological origin alongside a natural one. 

Level 5 relates to a “suspected passive technology,” where studies point to an artificial origin without any active behavior. 

Level 6 and 7 suspect more artificial technology, including evidence of “propulsion, maneuvering, or directed electromagnetic emissions.”

The latter ranks of the Loeb scale indicate the confirmation and risk of the presence of artificial technology, with Level 10 standing for a “confirmed artificial body on a collision course with Earth that would carry global consequences.”

Based on anomalies observed in 3I/ATLAS, Loeb put it on Level 4. The anomalies observed and deduced in the interstellar object include the object’s retrograde trajectory, which is aligned to within 5 degrees of Earth’s path around the sun.

Then comes the “anti-tail” of the object, which did not emerge from an optical illusion. The third and fourth anomalies shed light on the object’s unusual mass and its “fine-tuned path,” respectively. 

The abundance of nickel in comparison to nickel and the higher proportion of carbon dioxide in the gas plume of the object add to the unusual properties of 3I/ATLAS.

The negative polarization and the coincidence of 3I/ATLAS arriving from the direction of the “Wow! Signal” became two more anomalies, according to Loeb. 

The ninth anomaly draws attention to its rapid brightening and taking on a bluer color than the sun. The last point discusses the non-gravitational acceleration observed in 3I/ATLAS. 

Stay tuned for more updates.