3I/ATLAS: Strange Water Reveals the Comet's Ultra-Cold Origin

For only the third time in recorded history, humanity is watching a fragment of another star system fall through our own.

Unlike a homegrown comet that loops back every few decades, 3I/ATLAS is a true one-shot guest.

How astronomers caught an interstellar comet

The object was discovered on 1 July 2025 by the ATLAS survey, the Asteroid Terrestrial-impact Last Alert System, from its telescope in Río Hurtado, Chile.

That makes it only the third confirmed interstellar object, after the cigar-shaped 1I/ʻOumuamua in 2017 and comet 2I/Borisov in 2019.