In July, researchers using the NASA-funded Asteroid Terrestrial-impact Last Alert System survey telescope in Chile made an exceedingly rare discovery: a mysterious object passing through the solar system at far too high a speed to be bound by the Sun’s gravity. As the visitor made its closest approach to Earth, coming within just 167 million miles on December 19, an international team of researchers from the alien-hunting astronomy project Breakthrough Listen pointed the Green Bank Telescope — the largest single-dish radio telescope in the world — at 3I/ATLAS. In a yet-to-be-peer-reviewed paper, they revealed sobering — albeit probably expected —...