Interstellar object Comet 3I/ATLAS: What we know now
For only the 3rd time in history, astronomers have found an interstellar object hurtling through our solar system. The newly discovered space rock, now named 3I/ATLAS, could be as large as 12 miles (20 km) in diameter. And it’s soaring toward the sun at a blistering pace.
New interstellar object visiting our solar system
There’s a new object in the solar system headed toward the sun, and it came from interstellar space. Comet 3I/ATLAS is only the third-known interstellar object to visit our solar system. The previous two were ‘Oumuamua and Comet 2I/Borisov.
The Asteroid Terrestrial-impact Last Alert System (ATLAS) detected our new visitor on July 1, 2025. And the Minor Planet Center confirmed its interstellar nature on July 2, 2025, naming it 3I/ATLAS (or C/2025 N1). The “3I” means it’s the third interstellar visitor that we’ve found.
From a different part of our galaxy
Astronomers said this interstellar comet is likely older than our solar system. Our solar system formed some 4 billion years ago, and the comet might be as old as 7 billion years.
The comet is traveling on a steep path through the Milky Way galaxy. Astronomers have analyzed its trajectory, which shows it is not swinging around the sun and heading back out into the outskirts of our solar system. Instead it’s just flying by. And their analysis suggests Comet 3I/ATLAS originated from the Milky Way’s thick disk. This is an area of ancient stars orbiting above and below the thin galactic plane where the sun and most stars reside.
What we know about Comet 3I/ATLAS
Observations of the comet show it might have a diameter of nearly 12 miles (20 kilometers). This is much larger than the other two interstellar objects. Those were ‘Oumuamua’s at 200 meters across and Borisov at less than 1 kilometer in diameter.
Our new visitor will get its closest to the sun – at about 2 astronomical units (AU), or twice as far as Earth is from the sun – in October. As it reaches perihelion – its closest point to the sun – it will be traveling at almost 15,500 miles (25,000 kilometers) per hour.
The speedy nature of Comet 3I/ATLAS is more proof of its interstellar nature. It has to be moving at a blistering pace in order to escape the sun’s gravitational pull.
Marshall Eubanks, a physicist and VLBI radio astronomer and co-founder of Space Initiatives, said the comet will come within about 0.4 AU of Mars in October. That would make it just barely observable by the Mars Reconnaissance Orbiter.
It’s important for science
Having a visitor from another solar system is a rare opportunity for scientists, as NOIRLab said in a press release:
These visitors from faraway regions of the cosmos are valuable objects to study since they offer a tangible connection to other star systems. They carry information about the chemical elements that were present when and where they formed, which gives scientists insight into how planetary systems form at distant stars throughout our galaxy’s history, including stars that have since died out.
Locator maps for the new interstellar object
From now through the beginning of September, Comet 3I/ATLAS will be in the evening sky. For the rest of September and October it will be too close to the sun to see. But by November and December the comet will be bright after just passing the sun and also out of the sun’s glare. At this point it will be a morning object, not far from Venus.
Eddie Irizarry shared maps of the location of 3I/ATLAS. Eddie said in an email to EarthSky:
Although Comet 3I/Atlas is currently dim, advanced amateur observers might be able to photograph the new visitor by taking long exposure images through a telescope.
By August, the new comet should reach magnitude 16 and gradually improve, allowing more astrophotographers to capture this rare object.
The dim space rock is currently at about magnitude 16.7.
Bottom line: We have a new interstellar object visiting our solar system! Comet 3I/ATLAS is speeding through our neighborhood. Get finder charts here.
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