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Meet 3I/ATLAS: The Interstellar Comet Crashing Our Solar System Party

  • Writer: VP Promotions, The UBC Astronomy Club
    VP Promotions, The UBC Astronomy Club
  • 4 days ago
  • 4 min read

Every once in a while, the universe drops by with a surprise guest – and this time it’s a cosmic traveler from way out of town. Say hello to 3I/ATLAS, the newest interstellar comet to swing through our Solar System. Yes, interstellar, as in: not from around here.


If the first thing you thought was “Wait… like ’Oumuamua?”Correct. Except this time we spotted it early, it’s behaving like a comet should (well… mostly), and we actually get to study it in action rather than argue on the internet about its shape for years.


So let’s talk about why astronomers are buzzing, why some people are making alien jokes (again), and what makes this icy visitor so ridiculously cool.



So, What Is 3I/ATLAS?


Think of 3I/ATLAS as a cosmic drifter – a chunk of ancient ice and dust that formed around some distant star, got unceremoniously kicked out of its home system, and has been cruising through the galaxy ever since.


Then on July 1, 2025, the ATLAS sky survey telescope in Chile basically went, “Hold up… what’s that thing screaming through the sky?”


And just like that, we had our third ever confirmed interstellar object.


“3I” = third interstellar visitor. “ATLAS” = the telescope that spotted it.




This Thing Is FAST!


When astronomers first measured it, 3I/ATLAS was flying at about 137,000 mph. That’s fast enough to get from New York to Tokyo in roughly two minutes, assuming you don’t mind destroying the planet in the process.


Near the Sun, it ramped up to 153,000 mph.


And here’s the key: objects formed in our Solar System do not naturally move this fast unless something major slingshots them. Nothing did. This comet simply showed up going way too fast to be local.


This brings us to the important question…




How Do We Know It’s Interstellar?


Its orbit gives it away. Solar System objects follow orbits that are closed loops - circles, ovals, slightly weird shapes, but still loops. They’re bound to the Sun.


3I/ATLAS is not bound to anything here. Its orbit is hyperbolic, which means it has more than enough energy to escape the Solar System entirely. In plain language, it’s not staying for dinner.


A native comet doesn’t suddenly break free from the Sun unless it was kicked very hard by Jupiter or another giant planet. But 3I/ATLAS had no such encounter. It just arrived already moving faster than the Sun’s gravity could hold.


Combine a hyperbolic orbit, an incoming direction that doesn’t match any known comet family, and no planetary nudges, and the conclusion is obvious:It came from somewhere else in the galaxy.




What Does It Look Like?


Picture a dirty snowball the size of a mountain, wrapped in a glowing cloud of gas.


Here’s what NASA and Hubble tell us:

  • It’s somewhere between 440 meters and 5.6 kilometers wide

  • It has a bright, active coma (the fuzzy halo comets get when they warm up)

  • It’s outgassing mostly carbon dioxide, plus plenty of water-ice vapor


A classic comet, just with an interstellar passport.




Where Is It Going?


Good news: not toward Earth.


Its closest approach is about 1.8 AU, which is comfortably far away. Definitely not an apocalypse-movie situation.


It looped near the Sun on October 30, 2025, took in the scenery, and is now on its way back out into deep space. A true introvert: stops by once, stays briefly, and refuses to be tied down by gravity.




Why Scientists Are Obsessed With It


Interstellar comets are basically surprise care packages from other star systems. They carry:

  • ices formed around a different star

  • dust with unfamiliar chemical fingerprints

  • clues about planet formation in foreign environments


They’re rare and incredibly informative.


3I/ATLAS has already surprised researchers by:

  • brightening faster than typical Solar System comets

  • producing a strong (but natural) radio signal

  • showing lots of CO₂, hinting at a different birth environment


Every new observation is like peeling another layer off a cosmic mystery box.




And Yes… the Alien Jokes Have Started


Because of course they have.


The moment someone saw “radio signal,” people started whispering “interstellar probe.”Meanwhile, astronomers collectively sighed and explained, once again, that comets can make radio noise through completely normal physics.


So no, it’s not alien technology. 👽




Why You Should Care (Even If You’re Not a Space Nerd)


3I/ATLAS is a literal postcard from another solar system. It might contain materials from stars that died long ago, or from planets that never formed. It’s a message in a bottle tossed across the galaxy, and somehow, miraculously, it drifted past us.


That alone is extraordinary.




Final Thoughts


3I/ATLAS won’t be visible to most of us, and it won’t be back. But for a brief moment, it gives astronomers a rare chance to study the chemistry and physics of a world that formed under a completely different sun.


And honestly, there’s something magical about that. Once in a while, the universe sends us a visitor from far beyond our familiar space, just to remind us that the galaxy is wide, wild, and full of travelers passing through.


Blog Post Cover Image

Credit: Image: NASA, ESA, David Jewitt (UCLA); Image Processing: Joseph DePasquale (STScI)


 
 
 

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