There's a new comet in town. Or, a newly-discovered comet in our Solar System, to be exact.
On 1 July 2025, the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile, reported sightings of a comet that's entered our Solar System.
The comet, officially known as 3I/ATLAS or C/2025 N1, originated from interstellar space, NASA says, and has arrived in our Solar System from the direction of the constellation Sagittarius.
It's currently about about 420 million miles (670 million kilometres) away from Earth.
What we know about 3I/ATLAS
Since the first report on 3I/ATLAS, astronomers have been compiling archive observations made before the comet was even discovered.
They've been trawling the archives of three different ATLAS telescopes around the world, as well as the Zwicky Transient Facility at the Palomar Observatory in California.
The so-called 'pre-discovery' observations go all the way back to 14 June 2025, and other telescopes are reporting further observations since 3I/ATLAS was first reported.
It's thought to be as big as to 20 kilometres wide and travelling about 60 km/s relative to the Sun.
3I/ATLAS is what's known as an 'active comet', which means it heats up as it gets close to the Sun.
This is potentially exciting news for comet observers, as it could lead to frozen gases sublimating into vapour, carrying dust and ice particles and forming a glowing coma and tail.
Will 3I/ATLAS come close to Earth?
NASA says "the comet poses no threat to Earth," and it's expected to remain at a distance of at least 1.6 astronomical units (AU), i.e. 1.6 times the distance between Earth and the Sun.
That's about 150 million miles or 240 million km.
For context, comet 3I/ATLAS is currently 4.5 AU (416 million miles or 670 million km) from the Sun.
From the information gathered about 3I/ATLAS so far, astronomers are able to calculate what its orbit looks like.
It's expected to reach its closest approach to the Sun around 30 October 2025 at a distance of 1.4 AU (130 million miles or 210 million km), putting it just inside the orbit of Mars.
What does it look like?
As of yet, it's too early to say what interstellar comet 3I/ATLAS looks like.
NASA says its "size and physical properties are being investigated by astronomers around the world."
And, according to NASA, 3I/ATLAS should be visible through ground-based telescopes until September 2025.
After that time it will pass too close to the Sun to observe, but will reappear on the other side of the Sun by early December 2025, at which point it can be studied again.
