Astronomers say they’ve spotted the third interstellar object to be detected flying through our solar system. The object — initially known as A11pl3Z and now designated 3I/ATLAS — was discovered on July 1 by the Asteroid Terrestrial-impact Last Alert System, or ATLAS.
Early indications are that the 3I/ATLAS is behaving like a comet, and that it may be up to 12 miles (20 kilometers) wide. But don’t panic: This object has no chance of hitting Earth.
3I/ATLAS is currently about 416 million miles from the sun and zooming across the solar system at 130,000 mph. Its projected path is being determined more precisely through follow-up observations and analysis, including a review of “precovery” telescope images that recorded the object’s position but went unnoticed until the ATLAS astronomers reported their find.
The analysis suggests the object will have a close encounter with Mars and swing past the sun in October. Earth will be on the other side of the sun, which rules out making up-close observations or sending a probe. David Rankin, an astronomer with the Catalina Sky Survey, said in a series of Bluesky postings that the path of 3I/ATLAS through the solar system appears to have the highest eccentricity ever found.
This telescope image shows the object known as 3I/ATLAS at center. (Credit: David Rankin / Saguaro Observatory)
The discovery comes eight years after astronomers detected the first confirmed interstellar object, now known as ‘Oumuamua. That rocky object was shaped like a cigar, with an estimated length of 1,300 feet (400 meters) — 10 times its width. The unusual shape led some to speculate that ‘Oumuamua was an alien spaceship.
In 2019, astronomers spotted another interstellar object, a comet dubbed Borisov after its discoverer. Borisov’s diameter was estimated at about a kilometer (0.6 miles), with a tail extending nearly 100,000 miles (160,000 kilometers) in length.
Both of those previously detected interstellar objects sped through the solar system harmlessly and headed back into deep space, never to be seen again. That’s what’s expected to happen to 3I/ATLAS as well.
The object appears to be larger than ‘Oumuamua or Borisov, with estimates of its diameter ranging as wide as 12 miles. “Better data will refine the size estimate as well as the orbital parameters,” Harvard astrophysicist Avi Loeb wrote on Medium.
It also appears to be a comet. The International Astronomical Union’s Minor Planet Center noted “tentative reports of cometary activity,” including a marginal coma and a short tail of gas and dust. An alternate designation for the object, C/2025 N1, includes a “C” for comet.
Loeb has been a proponent of the controversial idea that some interstellar objects could be alien spaceships, and 3I/ATLAS could provide a fresh opportunity to test that out-of-this-world hypothesis. In his Medium posting, Loeb mentions the possibility of detecting “non-gravitational acceleration” — but even if such acceleration is detected, it could be due to natural outgassing from the object, as scientists suspect was the case for ‘Oumuamua.
“In the coming months, we will learn much more about A11pl3Z’s properties based on data from multiple ground-based telescopes including the new Rubin Observatory in Chile, as well as possibly the Webb Space Telescope,” Loeb wrote. “Stock your popcorn.”
This report was updated on July 3 with the Minor Planet Center’s confirmation of 3I/ATLAS’ status as an interstellar comet.
