In 2017 astronomers at Haleakala Observatory in Hawaii discovered something they had never seen before. It was an object from interstellar space passing through the solar system too fast to be captured by our sun’s gravity. They named it ‘Oumuamua’.
Oumuamua soon vanished back into deep space, leaving its mysteries behind. One of the strangest was the fact that, when it was close to the sun, the object changed course, accelerating through some force other than gravity. Comets often do this, as their frozen gases are vaporized by the sun’s heat. Erupting jets of dust and gas act like naturally-occurring rockets to change a comet’s path through space. But, researchers saw none of the usual gases, nor the dust needed to support this explanation. This oddity even led one astronomer to broach the possibility that Oumuamua might be an alien spaceship.
In 2021 Arizona astronomers proposed a new theory of Oumuamua that explains its strange behavior without alien technology. They proposed that Oumuamua was a chunk of nitrogen ice. Here on Earth, nitrogen is a gas in our atmosphere. But far out in the cold depths of space, nitrogen would be frozen solid.
If Oumuamua were made of nitrogen ice, it would have been shinier than an asteroid or comet, and thus smaller than otherwise expected. As it evaporated from the sun’s heat, it would need to expel only small amounts of gas to change course, and the nitrogen gas would be harder to detect than expected cometary gases. The surface of the dwarf planet Pluto is covered with nitrogen ice. Oumuamua might have been formed when a similar dwarf planet, orbiting a distant star, was destroyed in a collision.