ʻOumuamua: An Interstellar Object with Signs of a Probe

On 19 October 2017, the Pan-STARRS telescope in Hawaii caught an object leaving the Solar System. It was named ʻOumuamua, Hawaiian for “a messenger arriving from far away.” Its open, hyperbolic orbit showed that the Sun could not capture it. It entered from interstellar space, passed the inner Solar System, and continued outward. It was the first confirmed object known to have come from another star system.

Astronomers had only a few weeks to follow it. ʻOumuamua was too small, too distant, and too fast for any spacecraft to chase. Its brightness changed sharply as it rotated, so it had to be extremely elongated or flattened. It showed no clear dusty tail like an ordinary comet, yet its path received a small push that the Sun’s gravity alone did not explain.