An interstellar visitor just entered our Solar System
In July 2025, astronomers identified an exceptionally rare interstellar comet currently speeding through our Solar System. The object has been designated 3I/ATLAS and is only the third confirmed interstellar visitor ever discovered: the first was ‘Oumuamua in 2017, and the second was 2I/Borisov in 2019.
Discovery and observations
3I/ATLAS was detected on 1 July 2025 by the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) telescope located in Chile. Initially labelled C/2025 N1 (ATLAS), the Minor Planet Center (MPC) soon reclassified it as 3I/ATLAS, signalling its status as the third known interstellar object, writes EarthSky.
Following its discovery, astronomers reviewed archival images dating back to 14 June 2025, confirming the comet’s presence. Current observations place the object approximately 4.5 astronomical units (about 670 million kilometres) from the Sun, with an apparent magnitude of roughly 18.8—too faint for amateur telescopes to observe.
Orbit and closest approaches
3I/ATLAS follows a highly hyperbolic trajectory, unequivocally indicating an interstellar origin. It is travelling at a speed of 68 km/s (152,000 km/h) relative to the Sun and poses no threat to Earth.
The comet will reach perihelion (closest approach to the Sun) on 30 October 2025, at a distance of 1.4 astronomical units (210 million kilometres), inside the orbit of Mars. Its closest approach to Earth will occur on 19 December, at about 1.8 astronomical units (270 million kilometres) away, reports Space.com.
What do we know about the comet that entered the Solar System?
Researchers are currently studying the size and physical properties of 3I/ATLAS. Preliminary estimates suggest the nucleus could be up to 20 kilometres in diameter, though this remains uncertain. Observations have revealed a faint coma and a short tail, confirming that the object is indeed a comet rather than an asteroid.
Observation Opportunities
At present, even though it has entered our Solar System, the comet is only visible with large ground-based telescopes. As it approaches the Sun, it is expected to brighten slightly. It will be observable until September, after which it will be too close to the Sun to see. It will reappear in early December, providing further opportunities for observation.
Why Is 3I/ATLAS Special?
Interstellar objects are extraordinarily rare, and each visitor offers a unique chance for scientists to study material from beyond our Solar System. The discovery of 3I/ATLAS marks another milestone in astronomy and opens exciting new avenues for research into celestial bodies originating from interstellar space.
Read also: