After years of speculation, a team of scientists has finally determined what caused the peculiar orbit of the interstellar object known as Comet ‘Oumuamua. Despite its odd name, the comet was a remarkable discovery in its own right, being the first known object to come from outside our solar system.
Observed in 2017 by the Pan-STARRS1 telescope in Hawaii, ‘Oumuamua immediately attracted attention for its unusual properties. It was long, thin, and cigar-shaped, instead of the typical round or oval shape of comets, asteroids, and other space rocks. Its trajectory was also highly anomalous: it was moving much faster than any object in our solar system, and it seemed to be accelerating as it got closer to the sun.
Many theories were proposed to explain these odd features but not one could entirely square with the available data. Some astronomers thought that ‘Oumuamua might be an artificial object, like a probe or a spaceship, sent by some extraterrestrial civilization. Others suggested it might be a hydrogen iceberg or a chunk of frozen nitrogen that had been ejected from a distant star.
The truth, it seems, is both less fantastic and more mundane than any of these speculations. According to a study published in the journal Nature, Oumuamua’s strange orbit can be explained by its peculiar shape alone.
The study, led by Dr. Jane Luu at the Massachusetts Institute of Technology, used computer simulations to model the comet’s motion based on its observed characteristics. The researchers found that, because ‘Oumuamua is highly elongated, it experiences a slight but steady push from the sun’s radiation pressure that makes it deviate from a purely gravitational trajectory.
This effect, known as the Yarkovsky acceleration, arises from the fact that the surface of ‘Oumuamua heats up and cools down unevenly as it rotates. The parts of the comet that are facing the sun get hotter and emit more radiation than those in the shade, causing a net force that nudges the comet off course.
“It’s like having a sail that’s being blown by the wind,” said Dr. Luu in a press release. “The sail gets slightly pushed by the wind, but that’s enough to cause a significant deviation when you integrate it over millions of kilometers.”
The Yarkovsky acceleration is a well-known phenomenon that affects many objects in space, including asteroids and other comets. What makes ‘Oumuamua unique is the combination of its unusual shape and its high speed relative to the sun.
“We found that if you assume ‘Oumuamua is a flat, pancake-like object, which it looks like, then its motion matches up perfectly with the Yarkovsky effect,” said Dr. Luu. “That’s the smoking gun evidence that we’ve been looking for.”
Other scientists not involved in the study praised the work as a significant step forward in understanding one of the most enigmatic objects ever observed in space.
“This is a very elegant explanation for what was a very puzzling phenomenon,” said Dr. Kevin Walsh of the Southwest Research Institute. “It shows that ‘Oumuamua is not as weird as we thought, but it’s still an amazing discovery.”
The discovery of ‘Oumuamua has sparked renewed interest in the search for extraterrestrial life and the possibility of interstellar travel. While this latest study rules out the idea that ‘Oumuamua was an alien artifact, it also underscores the need for more systematic observations of objects that come from outside our solar system.
“Every time we look at something new in the universe, it teaches us something unexpected,” said Dr. Luu. “Who knows what else is out there that we haven’t seen yet?”