[Image: Wikicommons]
Astronomers have confirmed the discovery of a rare celestial visitor from beyond our Solar System.
The comet was first spotted on 1 July 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Río Hurtado, Chile, and its unusual trajectory immediately raised suspicions that it originated from interstellar space.
This was later confirmed by astronomers around the world, and the object was given its formal, catchy designation: 3I/ATLAS.
3I/ATLAS is only the third of its kind ever observed, following the famous 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019. It’s currently approximately 670 million kilometres from the Sun and will make its closest approach in late October 2025, passing just inside the orbit of Mars.
It is thought to be up to 20 kilometres wide and is travelling roughly 60 km/s relative to the Sun. It poses no danger to Earth, coming no closer than 240 million kilometres, which is over 1.5 times the distance between Earth and the Sun, so no stress there.
ESA astronomers are using telescopes in Hawaii, Chile, and Australia to monitor the comet’s progress. Some of these telescopes are owned by ESA, others are provided as part of longstanding partnerships. These efforts are part of ESA’s broader mission to detect, track, and characterise near-Earth objects, though 3I/ATLAS is not considered one, due to its distance from our planet.
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Scientists will now be interested in learning more about this interstellar visitor’s composition and behaviour.
3I/ATLAS is an active comet. If it heats up sufficiently as it nears our star, it could begin to sublimate – a process in which frozen gases transform directly into vapour, carrying dust and ice particles into space to form a glowing coma and tail.
By the time the comet reaches its closest point to Earth, it will be hidden behind the Sun, and is expected to only reappear by early December, offering astronomers another small window for study.
ESA is now preparing the Comet Interceptor mission. The spacecraft will be launched in 2029 into a parking orbit at the Sun–Earth Lagrange Point 2 (L2), lying in wait for a suitable target – a pristine comet from the distant Oort Cloud that surrounds our Solar System, or, unlikely but highly appealing, an interstellar object.
These icy travellers offer a rare connection to the bigger galaxy, and a fascinating insight into materials formed in environments completely alien to our own.
While it’s unlikely we will get to see the Comet Interceptor’s rendezvous with 3I/ATLAS, it’s a valuable test run for any further strangers that venture into our neck of the stellar woods.
[Source: IT-Online]
