3I/ATLAS has a ninth anomaly, as Loeb calls on 'science populariser' to explain all of them

Harvard scientist Avi Loeb has flagged a ninth anomaly in 3I/ATLAS. The interstellar comet has become the most mysterious object in our solar system ever since it was discovered on July 1. Loeb noted eight anomalies, features that raised doubts over the object being a comet. The ninth anomaly, he says, was revealed when 3I/ATLAS was at perihelion. According to data, the comet changed colour to a bright blue when it was at its closest point to the Sun. Typically, comets take on a red hue in this position. This happens because of the dust around comets that scatters the sunlight. He wrote that the interstellar object revealed a "rapid brightening and a colour bluer than the Sun." Its brightness also rose by several notches. The brightening and the change in colour were noted in a new paper. The authors wrote, “The reason for 3I/ATLAS’s rapid brightening, which far exceeds the brightening rate of most Oort cloud comets at similar distances from the Sun, remains unclear.”

The observations were made by STEREO (“Solar TErrestrial RElations Observatory”), SOHO (“SOlar and Heliospheric Observatory”) and GOES-19, launched in 2024, a weather satellite. Talking about the blue colour, Loeb wrote, "For a natural comet, this blue colour is very surprising. Dust is expected to redden the scattered sunlight, and the surface of 3I/ATLAS is expected to be ~20 times colder than the 5,800 degrees Kelvin at the photosphere of the Sun, resulting in it having a redder color than the Sun." He added, that this appearance at perihelion "is a ninth anomaly in the list of unexpected properties of 3I/ATLAS."

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Loeb challenges English physicist to explain the anomalies of 3I/ATLAS

Loeb has also challenged English physicist Brian Cox to explain the anomalies of 3I/ATLAS, who "argued forcefully that 3I/ATLAS is definitely a natural comet." Loeb said, "He acts as a science popularizer rather than a researcher who is engaged with the related science concerning 3I/ATLAS. In comparison, I wrote 11 scientific papers in recent months about 3I/ATLAS." He said, instead of making "sweeping statements", he should try to decode the anomalies of the interstellar visitor.

The anomalies of 3I/ATLAS

Loeb had earlier said that the interstellar object displayed eight anomalies, which hinted at it being an unnatural object. The first anomaly is its trajectory, which is aligned to within 5 degrees with the ecliptic plane of the planets around the Sun. He says there is only a 0.2% likelihood of this happening. The second is its anti-tail, which can be seen in the July and August 2025 observations. He says it displayed a sunward jet. Next is its size, as he says the nucleus of 3I/ATLAS is about a "million times more massive than 1I/`Oumuamua and a thousand times more massive than 2I/Borisov". However, it is moving at a mind-boggling speed of 200,000 km/hr, unlike the other two. There is a less than 0.1% chance of this happening.

He also says that its path and arrival time bring it within tens of millions of kilometres from Mars, Venus and Jupiter. Also, it wouldn't be visible from Earth at perihelion, which has a mere likelihood of 0.005%. Next is the gas plume around 3I/ATLAS, which he says contains much more nickel than iron, something mostly found in industrially produced nickel alloys. The gas plume around the interstellar object contains only 4% water by mass. The other issue is the extreme negative polarisation, "unprecedented for all known comets, including 2I/Borisov." Loeb also thinks that 3I/ATLAS could have sent the Wow! Signal since it is coming from the same direction.