What’s Driving the 'Not a Comet' Claim?
3I/ATLAS is a newly discovered visitor from outside our Solar System, and it’s already stirring debate. Some astronomers think it’s behaving like a comet, but others (including Dr. John Brandenburg) say it’s not a comet at all.
The reason? 3I/ATLAS has been seen releasing what looks like water vapor far from the Sun, at a distance where it’s normally too cold for ice to turn into gas. That’s strange, because most comets only “wake up” and start producing vapor when they’re much closer to the Sun.
Dr. Brandenburg says this puts it in the same category as Oumuamua which was another mysterious interstellar object that defied expectations back in 2017.
'3I/ATLAS is not a comet.', Dr. John Brandenburg says
On August 6, Dr. Brandenburg wrote:
3I/ATLAS is not a comet. Comets are 'dirty snowballs' of ices, and silicate dusts, usually dominated by water ice, but also more volatile ices like CO, which vaporize beyond Jupiter. 2I/Borisov displayed this, Oumuamua did not, 3I/Atlas is now emulating the latter. Be Alert!
Two days later, Dr. Brandenburg added the following to his claim:
After research, my opinion of 3I/ATLAS is unchanged: It is not comet, it's an Oumuamua object. Compared to Borisov, an interstellar comet, 3I/ATLAS remains bizarre. It emitted a cloud of water vapor too far from the Sun to explain, like watching an egg on a counter cook itself.
In short, Dr. Brandenburg is saying 3I/ATLAS doesn't fit the normal "comet" mold and is acting more like Oumuamua than Borisov which is the only confirmed interstellar comet we've seen.
How does 3I/ATLAS compare to Oumuamua and Borisov?
If you’re not an astronomer, here’s the quick backstory:
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Oumuamua (2017): The first interstellar object we discovered. It didn’t look or act like a comet, but it sped up slightly as if something was pushing it (possibly outgassing) though no vapor or dust was ever seen.
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Borisov (2019): A classic comet from another star system. It started producing vapor and dust far from the Sun, exactly as a comet should.
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3I/ATLAS (2025): Our latest interstellar visitor. It’s producing something that looks like water vapor but at a distance where normal comets should still be “asleep.”
That’s why some astronomers are scratching their heads.
How Strong Is the Oumuamua Analogy?
Dr. Brandenburg’s point is that unusual activity far from the Sun is rare. If what we’re seeing is truly water vapor, it’s hard to explain without something unusual going on.
In Oumuamua’s case, the mystery led to all kinds of ideas, from chunks of exotic ice to alien technology (though most scientists lean toward natural explanations).
With 3I/ATLAS, the question is whether it’s just a strange kind of comet, or if it’s another example of an interstellar object behaving in ways we don’t yet understand.
Open Questions We're Watching
Key Points
- Are we really seeing water vapor, or something else entirely?
- Could 3I/ATLAS have frozen gases trapped inside that are being released now?
- Is its shape or spin making parts of it heat up more than expected?
- Will its path through space show any unexplained changes, like Oumuamua's did?
The answers to these could help figure out whether Dr. Brandenburg's comparison holds up.
Editorial Note & Credit
All quotes in this article come directly from Dr. John Brandenburg on X. The discussion here is based on early observations, and the picture may change as more telescopes gather data.
3I/ATLAS will only be visible for a limited time, so scientists are racing to learn as much as they can before it disappears back into the depths of space.
