An interstellar object trespassing in our solar system known as 3I/ATLAS has captivated the public for months, and it's easy to see why.
For one, it's incredibly rare for any kind of space object originating from a star that's not our sun to be spotted visiting Earth's cosmic neighborhood. And for another, such an uncommon event has given rise to plenty of wild conspiracy theories about just what the object could be – including an infamous idea that it could be an alien spaceship.
But as 3I/ATLAS' renown (and infamy) only continue to grow, scientists around the world are racing to get a closer look at an object that will one day vanish from our sights forever. Early on, astronomers were able to determine with a high degree of certainty that the object is a comet, but work has continued to get a better idea of its size and physical characteristics.
Whether you're in need of an introduction to or a refresher about 3I/ATLAS, here's everything to know about the interstellar object.
What is 3I/ATLAS?
A look at 3I/ATLAS from NASA.
An object known as 3I/ATLAS made news in July when it was confirmed to have originated outside Earth's solar system.
The observation was reported to the Minor Planet Center, the official authority for observing and reporting new asteroids, comets and other small bodies in the solar system. The object, eventually confirmed to almost certainly be a comet and named 3I/ATLAS, was later confirmed to have interstellar origins after follow-up observations.
How did 3I/ATLAS get its name?
The "3I" in the object's name is due to its status as one of three interstellar interlopers ever discovered in our cosmic neighborhood. Comet Oumuamua, Hawaiian for “scout” or “messenger,” became the first interstellar object ever detected in the solar system in 2017, followed by the comet Borisov in 2019.
As for "ATLAS," that portion of the name is derived from the telescope credited with the find. The telescope in Chile – part of the NASA-funded Asteroid Terrestrial-impact Last Alert System, or ATLAS – was the first to spot what initially looked like an unknown asteroid on a path approaching Earth’s orbit.
What does 'interstellar' mean?
Observations of 3I/ATLAS's speed and trajectory confirmed to astronomers that it formed in another star system and was ejected into interstellar space – the region between the stars, according to NASA. For potentially billions of years, the comet has drifted on a journey from the general direction of the constellation Sagittarius in the center of the Milky Way that recently brought it into our solar system.
What's the difference between a comet and an asteroid?
Asteroids are made up of rocky material long left over from our solar system's formation. Most reside in the main asteroid belt between the orbits of Mars and Jupiter.
Telescope observations, though, helped astronomers determine that 3I/ATLAS displays all the telltale signs of a comet.
That's because the object is still active, meaning it's composed of not just rock, but also has an icy nucleus and a bright cloud of gas and dust, known as a coma, surrounding it. That material begins to heat up and spew out the closer a comet gets to the sun.
Webb, Hubble among telescopes to study interstellar visitor
Hubble captured this image of the interstellar comet 3I/ATLAS on July 21, 2025, when the comet was 277 million miles from Earth. Hubble shows that the comet has a teardrop-shaped cocoon of dust coming off its solid, icy nucleus.
Unlike comets bound to the sun's gravity, 3I/ATLAS is traveling on a hyperbolic orbit that will eventually carry it out of the solar system and back into interstellar space. That's why the world's astronomers and space agencies are racing to study planetary material that formed from another star.
A fleet of NASA space telescopes – including the Hubble Space Telescope and the James Webb Space Telescope – have already returned images and data back to Earth gathered from glimpsing the comet.
Astronomers don’t yet know exactly how big 3I/ATLAS could be, but estimates range from a few hundred feet to a few miles across, according to the European Space Agency.
Hubble's data also allowed astronomers to estimate the size of the comet’s solid, icy nucleus as anywhere from about 1,400 feet to 3.5 miles wide, according to NASA.
When did 3I/ATLAS make its closest approach to the sun?
An image interstellar Comet 3I/ATLAS captured by the Gemini South telescope in Chile, shows the comet’s tail. 3I/ATLAS is only the third confirmed interstellar visitor to our solar system.
The object came within 130 million miles of the sun on Oct. 30, just inside the orbit of Mars. For reference, the sun is about 93 million miles away from Earth.
In the lead-up to 3I/ATLAS making its closest approach to the sun – a moment known as perihelion – the object was expected to steadily lose mass as frozen gases on its surface transformed into vapor, carrying dust and ice into space, according to the ESA.
How fast is 3I/ATLAS flying through space?
When it was discovered, 3I/ATLAS was whizzing at about 137,000 miles per hour, according to NASA.
The interstellar visitor, though, was expected to only pick up speed – reaching as fast at 153,000 mph – as it continued its journey toward the sun.
Now that it's moving away from the sun, the comet's speed will decrease as the sun's gravity pulls it back. By the time 3I/ATLAS leaves our solar system, it will be traveling at the same speed as when it entered, NASA says.
Is 3I/ATLAS a threat to Earth? How close will it get?
The comet 3I/ATLAS is not in danger of hitting Earth.
While 3I/ATLAS has been intermittently spotted since disappearing on the other side of the sun, the object will fully reappear in December, making it visible once again from our planet.
The object will continue making its way for its closest approach to Earth, which is projected to happen Dec. 19, when it comes within about 170 million miles of our planet – or about twice the distance between Earth and the sun. Is 3I/ATLAS an alien spaceship?
The strange outsider's jaunt through Earth's neighborhood has sparked widespread public fascination and plenty of outlandish conspiracy theories regarding its nature.
One particularly famous idea – put forth by a Harvard astrophysicist named Avi Loeb – is that 3I/ATLAS could be an alien spaceship. Though Loeb has conceded on publishing platform Medium that the object is "most likely a comet of natural origin," he has not ruled out the possibility that it could be alien technology.
"The implication of alien technology would be huge and therefore we must take this possibility seriously," Loeb wrote at the end of October.
Kim Kardashian, other celebrities, express interest in 3I/ATLAS
Loeb's theory, though, is a major reason why obsession with 3I/ATLAS has transcended the academic world of astronomy and made the object a pop culture phenomenon.
For instance, Kim Kardashian, a reality television star with hundreds of millions of social media followers, recently sought the "tea" – slang for "details" – on the interstellar visitor. In a recent exchange on X with NASA Acting Administrator Sean Duffy, Kardashian asked, “what’s the tea on 3I Atlas?!?!!!!!!!?????"
Duffy, an appointee of President Donald Trump, responded with a brief explanation on how the comet got its name, and added an important disclaimer: "No aliens. No threat to life here on Earth."
Jupiter spacecraft could be next to get a look at 3I/ATLAS
Spacecraft orbiting other planets have also gotten a look at 3I/ATLAS, including two ESA orbiters near Mars whose observations have allowed scientists to better understand the object's trajectory.
The ESA’s Jupiter Icy Moons Explorer (Juice) will be among the next spacecraft to observe the comet between Nov. 2 and Nov. 25, when the object is expected to be in a "very active state" following its closest approach to the sun. But because the spacecraft is so far from Earth on the other side of the sun, scientists don't expect to receive its observations until February, according to the ESA.
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