Is Comet 3I/ATLAS an alien spacecraft?

If you don’t hang out in the wilder areas of YouTube or TikTok, you may be thinking, “Wait. What? Is this a thing? The answer is no, right? Right?”

The answer is no. Comet 3I/ATLAS is not an alien spacecraft. But it is very interesting in its own right. The I in its name stands for “interstellar,” and the 3 signifies that it’s the third known interstellar object, meaning that it entered our solar system from interstellar space.

Such objects are rare opportunities to directly study pieces of other stellar systems. Comet 3I/ATLAS is from the Milky Way’s thick disk, which is an older part of the galaxy, suggesting that the object is billions of years older than our planetary system.

Much of the discussion about whether Comet 3I/ATLAS is an alien spacecraft has been driven by the blog and media appearances of Harvard University astronomy professor Avi Loeb, who believes that other astronomers have been too quick to dismiss that possibility. For example, Loeb has claimed that evidence of cometary activity has actually been caused by astronomers blurring the object’s image by incorrectly tracking it in the sky.

However, as astronomer Carl Sagan said, “Extraordinary claims require extraordinary evidence.” Many astronomers have responded to Loeb’s point about the blurred image with evidence that the comet has been tracked correctly. The consensus among astronomers is that 3I/ATLAS shows cometary behavior because it’s a comet, albeit one from another stellar system.

Why would anyone think that such objects could be alien spacecraft in the first place? One good reason is that humanity has already created five “interstellar objects.” The NASA space probes Pioneer 10 and 11, Voyager 1 and 2, and New Horizons are leaving our solar system, never to return. Even if humans never go to other stars, some of our technology will. Perhaps spacecraft created by beings on other worlds have gone beyond their stellar system.

An interesting paper by astronomer James R.A. Davenport and collaborators points out that it would be worthwhile to check interstellar objects for signs of unnatural activity. For example, if such an object changed its orbit in an unusual fashion, had a strange shape, had an obviously artificial surface, or was transmitting in some way, that would be a strong sign that the object was not a normal comet. Such weird behavior would be easy to see with the observations of interstellar objects that astronomers currently make. Comet 3I/ATLAS has not done anything so odd.