From the depths of interstellar space, a comet designated 3I/ATLAS has arrived in our solar system carrying chemistry that does not belong to it — water enriched in heavy hydrogen at levels thirty times beyond anything found in our own ancient comets. Measurements from the James Webb Space Telescope and other observatories suggest this visitor may have formed ten to twelve billion years ago, in a colder, metal-poor environment predating our Sun by billions of years. It is a rare moment in science: a piece of another planetary system, from another epoch of the galaxy, briefly close enough to re