Astronomers rarely pay much attention to objects that are no more than half a mile long and that are out of sight within months of their discovery. When such an object comes from outside the solar system, though, they’re all in.
That was the case with ‘Oumuamua, which was discovered in late 2017, shortly after it passed closest to the Sun. Calculations of its path showed that it came from another star system, and that it would leave our own system in a hurry.
So astronomers tracked the object with telescopes on the ground and in space. They found that it probably was shaped like a cigar, that it was tumbling, and that it was brighter than the comets and asteroids in the solar system. And they found that it sped up after it passed the Sun — something that comets and asteroids don’t do.
Yet most studies have concluded that it probably was a comet or asteroid. As it got close to the Sun, some of its frozen gases vaporized. They rushed into space as “jets,” causing the object to tumble — and perhaps causing its acceleration. Some of the gas may have fallen back on to ‘Oumuamua, coating it with fresh, bright ice.
One study, though, said the object could have an artificial origin. Its odd acceleration and other factors suggest that it was acting like a solar sail, which is pushed forward by sunlight. So the researchers said that perhaps ‘Oumuamua was a probe dispatched to study other star systems — including our own.