Comet or alien probe? 3I/ATLAS just flew into our Solar System
Rare interstellar visitor the size of Manhattan carries secrets from distant star system
3I/ATLAS is called a comet. Except that, upon closer look, it doesn't look like a comet.
Dubbed as an "unusually fast" celestial object from another star system, it has officially joined our solar system.
One astrophysicist says it's quite possibly an alien probe.
Moving 209,000 km/h relative to the Sun — the fastest ever for a solar system visitor — it's the third confirmed "interstellar" object to visit our solar system, a rare cosmic wanderer originating from beyond our Sun's gravitational pull.
What is it?
It’s a frozen relic from another star system. Harvard astrophysicist Avi Loeb considers Comer 3I/ATLAS as an “extraordinary anomaly".
Potentially, it could offer a snapshot of alien planetary formation.
Unlike typical comets born in our solar system, which follow elliptical orbits, 3I/ATLAS follows a "hyperbolic" trajectory.
That means: it’s on a one-way path through our neighbourhood before exiting back into interstellar space.
The alien-probe hypothesis was offered by Harvard astrophysicist Avi Loeb (detailed in his book “Extraterrestrial”), he posits that the comet may have been sent by aliens, sparking intense debate among astronomers.
He cites its unusual speed and "extremely unusual path".
Many dismissed the idea as speculative, but Loeb maintains that “extraordinary anomalies require extraordinary explanations.”
With 3I/ATLAS, he sees a familiar pattern.
Still, most scientists currently categorise 3I/ATLAS as a “likely comet”, Loeb argues that such assumptions may lead us to overlook important clues.
Loeb isn’t saying aliens definitely sent it. But he insists that the scientific method demands we investigate without prejudice, especially when something doesn’t fit existing models.
“If we keep dismissing the possibility of non-natural origin simply because it’s ‘too wild,’ we risk missing out on the truth,” he argues.
When was it discovered?
It was discovered in July 2025.
How was it discovered?
On July 1, 2025, the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Río Hurtado, Chile, first spotted the comet at about 420 million miles from the Sun.
Initial images showed no obvious cometary features, but follow-up observations on July 2 by telescopes like the Deep Random Survey in Chile, Lowell Discovery Telescope in Arizona, and Canada-France-Hawaii Telescope revealed a faint coma (a hazy envelope of gas and dust) and a short tail about 3 arcseconds long.
This confirmed its cometary nature and interstellar origin due to its unbound orbit.
Why is it called 3I/ATLAS?
The name breaks down simply: “3I” marks it as the third interstellar object (after 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019), with “I” for interstellar.
“ATLAS” honours the survey that found it.
The Minor Planet Center officially designated it on July 2, 2025, after global astronomers verified its extrasolar path.
What is its trajectory and speed?
3I/ATLAS hurtles through space at a blistering hyperbolic excess velocity of 58 km/s (about 130,000 mph or 209,000 km/h) relative to the Sun — the fastest ever for a solar system visitor.
This speed, built up over billions of years from gravitational encounters with distant stars, ensures it won't be captured by our Sun. It entered from the direction of Sagittarius and will exit toward Pegasus.
Perihelion (closest to the Sun) is expected on October 29-30, 2025, at 1.4 AU (130 million miles, inside Mars’ orbit). By March 2026, it'll cross Jupiter's path, fading from view by December 2025 in constellations Virgo and Leo.
Does it pose a threat to Earth?
Absolutely not. At its closest, 3I/ATLAS will be 1.8 AU (170 million miles) from Earth — over four times the Earth-Moon distance — posing zero collision risk. NASA and ESA emphasize it's a safe, distant observer, far too remote to influence our planet.
What does it look like and how big is it?
Early Hubble images from July 21, 2025, show a teardrop-shaped dust cocoon around its icy nucleus, with a coma spanning 2.5 arcminutes and a growing tail.
It's the largest known interstellar object, with a nucleus diameter estimated at 3.5 miles (5.6 km) upper limit, though some data suggest up to 80 miles (128 km) and a mass over 33 billion tons — orders of magnitude bigger than predecessors.
By September 2025, Gemini South Telescope captured its reddish, dusty coma, hinting at solar system-like dust but with unique traits.
What's unusual about its composition?
JWST and SPHEREx observations reveal a peculiar chemical profile: unusually high carbon dioxide and water ice, a blue-green glow from an unidentified molecule (lacking typical dicarbon for green hues), and an "extreme" iron-to-nickel ratio in its coma—far from solar system norms or 2I/Borisov.
This suggests formation in a metal-rich environment around another star. Non-gravitational acceleration is minimal (<15 m/day²), indicating low outgassing despite activity.
How are scientists studying it?
NASA's Hubble, JWST, and SPHEREx, plus ESA’s Mars Express and Juice (Jupiter mission) probes, are tracking it for size, composition, and activity. Ground telescopes like Gemini South enable real-time public viewing.
Over 4,000 measurements from 227 observatories refine its path. These efforts compare it to local comets, probing interstellar chemistry without a dedicated flyby mission.
Why does it matter?
As a pristine sample from another star system, 3I/ATLAS unlocks secrets of distant planet formation, shared cosmic building blocks, and object ejection dynamics.
Its anomalies challenge models, fueling debates on interstellar visitors' frequency — why so few giants? Amid hype (alien probes? doomsday?), it's a natural "messenger," enriching our galactic perspective without drama.
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