A third visitor from another star system is passing through our solar system
An object called 3I/ATLAS is crossing our neighbourhood on a path that shows it formed somewhere else. It is only the third such visitor astronomers have caught.
- Institutions
- ATLAS survey, NASA, European Southern Observatory
- Reported
- 2025
- Status
- Independently established and broadly accepted.
No imagery is attached yet. Agency imagery is free to use with a credit line, so anything added here will carry one.
What they found
In July 2025 a survey telescope in Chile picked up a faint moving point of light that turned out not to belong here. Astronomers named it 3I/ATLAS. The 3I means it is the third interstellar object on record, after 1I/'Oumuamua in 2017 and 2I/Borisov in 2019. It is a comet, and it has been shedding gas and dust as it warms on its way past the Sun.
How they found it
Its orbit gives it away. Everything born in our solar system travels on a closed loop around the Sun, held by the Sun's gravity. 3I/ATLAS is moving too fast for that, on a path that opens outward rather than closing, which means it arrived from interstellar space and will leave again. Astronomers work this out by measuring its position over many nights and fitting a curve to the motion, the same arithmetic used for any comet.
Why it matters
Interstellar objects are physical samples from other star systems that arrive at our doorstep. We cannot yet send a spacecraft to another star, so a visitor that comes to us is the only way to study material that formed around a different sun. Each one is a chance to ask whether the ingredients that built our planets, and eventually us, are common elsewhere or unusual. Three known visitors is a small sample, but it is three more than we had a decade ago.
What this does not mean
An unusual object is not evidence of alien technology. Everything observed about 3I/ATLAS so far is consistent with a natural comet: it has a coma of gas and dust, and it brightens as it nears the Sun the way comets do. Some researchers have published estimates suggesting it may be considerably older than the Sun, based on where in the galaxy its trajectory implies it came from. Those are inferences from its motion, not measurements of its age, and they carry real uncertainty.