3I/ATLAS is a comet, a ball of ice, dust, and frozen gases—or a “cosmic snowball,” as NASA calls them. As they approach the sun, they heat up and develop the long tails characteristic of most comets. The vast majority of the comets we see originate from the Kuiper Belt or the Oort Cloud, two distant regions within our solar system. But comet 3I/ATLAS formed elsewhere in the galaxy and is only passing by. Once it exits our solar system, it will never return.