Astronomers have just detected 3I/ATLAS, only the third known interstellar comet to pass through our solar system. Discovered July 1 by the ATLAS survey in Chile, its trajectory confirms it came from beyond our solar system, following in the footsteps of ‘Oumuamua (2017) and Borisov (2019). Early estimates suggest 3I/ATLAS could be much larger than Borisov—possibly 10 km across. As it approaches the sun in October, scientists are racing to study its composition and behavior. Each interstellar visitor is a rare chance to directly sample material from another star system.