An interstellar comet is passing through our solar system: here is everything you need to know.
Comet 3I/ATLAS was first discovered on July 1, 2025, spotted by the NASA-funded ATLAS survey telescope in Chile, and believed to have originated from interstellar space. This is the region between star systems within a galaxy, beyond the sun’s magnetic field and where solar wind influence ends. It sometimes referred to as the space between the stars.
Comet 3I/ATLAS represents just the third object in history to be known to have entered our solar system from outside; its name, 3I, represents ‘third interstellar’ object.
When Was 3I/ATLAS Closest to Earth?
The 3I/ATLAS comet came closest to Earth on December 19, at around 1 a.m. EST.
At this point, it was around 168 million miles from Earth. NASA has stressed that the comet poses no threat to Earth—this number is still more than 700 times the distance between the Earth and the moon.
Was 3I/ATLAS Visible to the Naked Eye?
Comet 3I/ATLAS was not visible to the naked eye. NASA urged stargazers to check out any observatories or skywatching events in their local area for the best shot at spotting the visitor to the solar system.
It was also visible through telescopes, looking east to northeast in the pre-dawn morning, under the star Regulus in the constellation Leo.
There is still a chance to see it, however—the Virtual Telescope Project is to host a free livestream, starting at 11 p.m. ET on December 19, sharing telescope views of the comet from observatories in Manciano, Italy.
The event is weather-permitting; the livestream was delayed after rain halted a planned broadcast on Thursday night.
3I/ATLAS trajectory
Comet 3I/ATLAS is on a hyperbolic trajectory: it moves too fast to be bound by the sun’s gravity, and, unlike other objects, is not bound by the orbital path around the sun.
It is passing through our solar system, having come from interstellar. NASA reports that it formed in another star system and has been drifting for millions, or even billions, of years.
Comet 3I/ATLAS approached our galaxy from the direction of the Sagittarius constellation, in the central region of the Milky Way.
On October 30, the comet was at its closest approach to the sun, and inside the orbit of Mars, reaching about 130 million miles from the sun.
It then passed behind the sun, but in early December, emerged from the other side, and became visible again.
The comet will continue its onward trajectory, not trapped in any orbit, and will eventually head out of our solar system for good, according to Space.com.
Do you have a tip on a science story that Newsweek should be covering? Do you have a question about comets? Let us know via science@newsweek.com.
