For generations, physicists have mapped the universe's visible edges while knowing that most of what exists lies beyond their instruments' reach. Now, a signal detected in Earth's magnetic field — one that defies every known explanation — has raised the possibility that dark matter, the invisible scaffolding of the cosmos, has finally made itself known. The finding is unconfirmed, the scientific community appropriately cautious, but the moment carries the particular weight of a question humanity has been asking since the stars first seemed to move in ways that didn't add up.