Top 10 Strange Facts About Interstellar Object 3i/Atlas

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Matrix link: https://docs.google.com/spreadsheets/d/1RlVdilfYmZxncbT_QFgF822Ie6-r4dWFBJqaHvRFVD4/edit?gid=0#gid=0

Welcome to WatchMojo, and today we’re counting down our picks for the Top 10 Strange Facts About 3I/Atlas - as only the third interstellar object ever discovered, this stranger from the stars has captured our collective interest, making us wonder if it truly is just a regular ol’ comet from another world…or possibly something even more alien.

#10: From a Solar System Far, Far Away

The interstellar comet dubbed 3I/ATLAS was first reported on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System - or, ATLAS, a NASA-funded survey telescope in Chile. It was discovered that “pre-discovery” observations extended back as far as June 14, 2025. During this discovery period, it was observed to not follow a closed orbital path around the sun, but a hyperbolic orbital path. Most comets, being bound by gravity follow an elliptical path, yet 3I/ATLAS appeared to be passing through our neighborhood - rather than orbiting. Thus it was named “3I/ATLAS” - the “I” standing for “Interstellar Object” number 3, discovered by ATLAS.

Sources:

https://science.nasa.gov/solar-system/comets/3i-atlas

#9: A Green Glowing Coma

As they get close to the sun, comets develop an atmosphere that surrounds them called a “coma”. It’s a cloud of dust and gas, growing brighter and bigger as the sun heats up the materials on the comet, including ice - these become gases that can be observed by astronomers. As 3I/ATLAS recently came around the other side of our sun, it was observed to be glowing green! This is due to diatomic carbon particles, which are excited by UV rays like those from the sun. This is normal for comets, but since 3I/ATLAS is making enough gas to be detectable by researchers and yet not enough for a usual tail - that’s where it gets a bit strange!

Sources: https://www.livescience.com/space/comets/irradiated-comet-3i-atlas-glows-green-and-hides-its-tail-in-new-image

#8: Older than the Sun Itself?

The James Webb Telescope observed that 3I/ATLAS’ surface has been irradiated over billions of years - in fact, it may now be made up of more irradiated material than whatever it was formed with in its birthplace. From these observations, added to some computer simulations, it was determined by researchers to have such “extreme” levels of carbon dioxide due to space radiation being absorbed over its lifetime - which is estimated at 7 billion years! This would make it by far the oldest comet we’ve ever seen - and even 3 billion years older than our own 4.6 billion-year-old solar system, including our very own sun!

Sources: https://www.livescience.com/space/comets/comet-3i-atlas-has-been-transformed-by-billions-of-years-of-space-radiation-james-webb-space-telescope-observations-reveal

#7: A Light Signature Like No Other

The illumination from sunlight cannot explain what Harvard Astrophysicist Dr. Avi Loeb is seeing from 3I/ATLAS. He’s been meticulously following the comet along its journey and has calculated the luminosity needed by the comet in order to be as bright as it has been observed. He realized the brightness profile around the object actually leads him to believe that 3I/ATLAS’ nucleus “produces most of the light” being observed! Of course, he is open to what this might mean - either a natural explanation, or even possibly a nuclear-powered alien technology coming to visit our neighborhood. At this point, it is only “a blind date of interstellar proportions” which Professor Loeb believes we should keep researching to find the answers.

Sources: https://avi-loeb.medium.com/does-3i-atlas-generate-its-own-light-e9775594afc5

https://youtu.be/pQ8tRs1Zg5g?si=IWBsKpXcaMh3R4gf

#6: Mysterious Propulsions

Until December, we won’t be certain, but Dr. Avi Loeb - professor of science and director of Harvard’s Institute for Theory and Computation - believes that there could be an alien explanation for 3I/ATLAS’ recently observed mysterious propulsion. He believes we should keep a close eye on it during December to see if it begins to show indications of a natural phenomenon, rather than the alternative. He believes that "If we do not observe a dense cloud of gas around it in December, then cometary evaporation is not the explanation of its nongravitational acceleration…Instead, it might constitute a technological signature of a propulsion system."

Sources: https://www.newsweek.com/3i-atlas-gets-mystery-acceleration-harvard-astronomer-behind-alien-theory-10971625

https://youtu.be/pQ8tRs1Zg5g?si=jTZ1xu-mNC-oIMyR

#5: Strange Temperature Reactions

3I/ATLAS has also captured attention because it appeared to be shedding water in a region far from the sun, which is odd for a comet. This was even observed when the object was approximately three times the earth’s distance from the sun away, during which time water was “escaping” at an astonishing rate of about 40 kilograms per second - roughly that of a high-powered fire hose. Researchers believe that this could be the result of sunlight warming tiny ice particles released from deep within the nucleus of the comet, vaporizing and feeding the surrounding cloud of gas. This unprecedented behavior may indicate layers of ice within the comet - possibly dating all the way back to the comet’s origin!

Sources: https://phys.org/news/2025-10-physicists-ultraviolet-fingerprint-interstellar-comet.html

#4: Cosmic Chemical Makeup

Researchers worked alongside the observations from the James Webb Telescope in an attempt to understand the unusual chemistry of 3I/ATLAS. The comet has been observed shedding nickel without much iron, which Dr. Avi Loeb described as “very surprising because the only place we find nickel without iron is in industrial production of nickel alloys.” The unusual chemical signature detected by researchers suggests that the nickel may be released through processes that actually work at much lower temperatures, instead of the usual way - transformation of solid to gas, called sublimation, which generally requires much higher temperatures.

#3: The Titan of Interstellar Travelers

Of all the interstellar objects discovered thus far, our third - 3I/ATLAS - takes the cosmic cake for size. According to Dr. Avi Loeb “...it’s the size of a city…a million times more massive than the first interstellar object that we discovered eight years ago.” The interstellar giant punches far above its class at an estimated 3.5 miles, or 5.6 kilometers, in diameter. That makes the third interstellar object much larger than its two predecessors - the first, 1I/’Oumuamua, was only estimated to be a few hundred meters across, and the second, 2I/Borisov, was estimated to be even smaller than typical solar-system comets at roughly half a mile across.

Sources: https://science.nasa.gov/solar-system/comets/3i-atlas/

https://youtu.be/pQ8tRs1Zg5g?si=MqlUE8HzB2Fj6tu5

https://www.space.com/astronomy/comets/new-interstellar-object-3i-atlas-everything-we-know-about-the-rare-cosmic-visitor

https://science.nasa.gov/solar-system/comets/2i-borisov/

#2: Recent Deviations

As 3I/ATLAS made its way around our sun, another peculiar observation was discovered by researchers. The interstellar object appeared to deviate from the path researchers were expecting it to travel if driven by gravity alone. This particular change in velocity is comparable to a jet expelling approximately five billion tons of material, which according to Dr. Avi Loeb would be required in order to produce an equivalent recoil effect. Once 3I/ATLAS rounded its path closest to the sun on October 29, 2025 researchers observed a set of more than seven “jets” around it, with some pointing towards, and some pointing away from, the sun. This leads us all to ask the question posed by Dr. Loeb: “Is this technological in origin?”

Sources: https://youtu.be/pQ8tRs1Zg5g?si=Ir_UVlx4lq5xCh_5

https://avi-loeb.medium.com/a-complex-jet-structure-emanates-from-3i-atlas-after-perihelion-1cc7f8ec7b81

https://youtu.be/SGG4wuqcLdU?si=1ti1j1bWhw_d6nSS

#1: Shape-Shifting Tail

One of 3I/ATLAS’ most striking anomalies is its tail - or lack thereof, for the most part. Harvard Astrophysicist Dr. Avi Loeb has been studying the comet since its discovery, and continues to discuss how strange the tail is in comparison with the tails of most comets. In one paper he wrote that 3I/ATLAS showed “an elongated coma similar to a cometary tail but pointing in the direction of the Sun” sometimes referred to as an “anti-tail”. Breaking updates continue to be made - the most recent being that the object doesn’t seem to have a tail at all now that it’s being observed nearer to our Sun - and ourselves.

Sources: https://youtu.be/C4vUxUbU1oc?si=BI6xduYN1orHEhgW

https://arxiv.org/abs/2509.07771

As the updates continue to roll in about our interstellar visitor, please share anything we’ve missed along the way in the comments and let us know what YOU think is the strangest thing about the legendary 3I/ATLAS.