Scientists Solve the Mystery Behind the Oumuamua 'Alien Spacecraft' Comet

The comment known as Omuomua, Hawaiian for visitor from afar, sailed through our solar system in 2017 and right away made news. Its small size, barely longer than a football field, and strange elongated shape made it an odd cosmic spectacle. But Omuomua did something unusual too. It sped up as it was leaving the solar system, far more than ordinary comments do when they're flung away by the sun's gravity. That led to some wild speculation that Omuomua was actually an alien spacecraft buzzing our corner of space. Now a new paper in nature explains the acceleration and alas, no aliens are involved. Instead, the researchers concluded the water ice inside the comet was cold enough when it was in deep space that it entered what's known as an amorphous state with Swiss cheese-like pockets in it.

Gaseous hydrogen filled those pockets. When the comet entered our solar system, the sun warmed the ice enough to cause it to take its usual crystalline state, squeezing the pockets and causing the hydrogen to exit the comet in powerful plumes, which led to the mysterious acceleration. That explanation is not as exciting as the extraterrestrial one, but it has the benefit of being good, solid science. Meantime, the wait for ET goes on.