It’s been over a month since this site’s last update on the most fascinating astronomical event of the year, 3I/ATLAS. The general run of astronomers and astronomical organizations keep insisting on calling the cosmic interloper a “comet,” but it is so very different from all previous solar system comets that the term seems stretched.
It’s odd how strict on nomenclature — developing and enforcing a discipline-wide definition — astronomers were when they demoted Pluto from “planet” to “dwarf planet,” in 2006, but now give so much latitude to “comet” when the current object displays so many anomalies.
How many anomalies?
Harvard astrophysicist Avi Loeb has documented up to 15 anomalies for the interstellar object 3I/ATLAS (also known as C/2024 S1), based on his recent writings and interviews where he compiles and expands on peculiarities in its composition, behavior, trajectory, and other traits that deviate from typical comets.
Some sources reference 14, but his most comprehensive recent list hits 15.
The most recent anomaly he highlighted is the alignment of 3I/ATLAS’s axis (center of rotation) with its persistent sunward direction. Comets tumble in a random, “bad-punt football” fashion; 3I/ATLAS entered our observational ambit headed for a flyby, but (we discovered later) with its rotational axis always pointing at the Sun — and then when nearest the Sun, it smoothly flipped, with the other pole also pointing within 8 degrees to the solar system’s gravitational center.
And all the while there was an “anti-tail” pointing out of its solar-side pole, tightly focused like a urine stream, not a sneeze — comet tails point away from the Sun, and usually resemble sneezes!
This is all very odd. The anti-tail is nudging the trajectory outward from the Sun, bringing the object closer to Jupiter than initial calculations indicated. Why?
Well, if it is an artificial object, Loeb suggests a rationale: “If 3I/ATLAS is technological in origin, it might have fine-tuned its trajectory with the help of thrusters so as to arrive at Jupiter’s Hill radius. In that case, the multiple jets observed around 3I/ATLAS in its post-perihelion images … might have been used for the slight orbit correction needed to result in min{D}=H.”
There are a lot of ifs here, of course, and Loeb himself says the bets are still favoring “natural object.” But the object is so weird that we know little of its nature. We may understand more of the whats of the object, after several months of observations, but few of its whys. Calling it a comet seems less justified than demoting Pluto. And finding excuses not to investigate this fascinating traveler is, as Loeb argues, the exact wrong lesson to draw.
But if you are looking for an informed mainstream view, consult Vladimir Putin, who insists on calling 3I/ATLAS a comet: “Our scientists are aware of what is happening. Moreover, this is a comet from another star, so it behaves differently from comets of our galactic [sic] origin. It has a different shell and as it approaches closer to the Sun, slightly different processes occur on its surface, including in the field tail of this rocket. Things look different there, but it’s quite large. I think somewhere between 2 to 6 kilometers. Look, the moon is 400,000 kilometers away from us. And the object you are talking about is hundreds of millions of kilometers away. I don’t think it poses any threat to us. We’ll let it go to Jupiter. And at the beginning of next year, the comet will leave the solar system.”