The first guest from an alien star in the solar system, the asteroid Oumuamua experienced a powerful collision before reaching us.
The unusual rotation of the asteroid Oumuamua was the result of a collision with another celestial body that occurred before the cigar-shaped asteroid approached the solar system. This is the conclusion reached by a group of astronomers who analyzed the movement of Oumuamua. Scientists describe the results of their work in an article published in the journal Nature Astronomy.
The first object that flew into our planetary system from another star, Oumuamua, was noticed in October last year and has been of great interest to scientists since then; they even managed to check it to see if it was a message from aliens. It is distinguished from other known celestial bodies by both its origin and form: it is almost eight times longer in length than in width, and somewhat resembles a giant cigar.
Oumuamua's journey through interstellar space has been going on for several hundred million years, and he spent some of this time in a very unusual, at first glance, chaotic rotation. Optical photometry data from Oumuamua's closest approach to Earth allowed astronomers at the University of Queensland, Australia, to describe this rotation and infer what caused it.
Some less elongated asteroids in the solar system rotate in a similar way, and the reasons for such rotation can be different, the authors of the article note. Among them are tidal forces that acted on the body during close passage near massive planets, shock effects, as well as the Yarkovsky-O'Keefe-Radzievsky-Paddeck effect (NORP effect), which occurs under the action of stellar radiation.
But for Oumuamua, only one of these reasons is most likely, namely, a collision with another large body, the researchers concluded.
Oumuamua is now heading out of the solar system; in May of this year it will go beyond the orbit of Jupiter, and in January next year it will be beyond the orbit of Saturn. But even after flying out of the orbit of Neptune, and much later, it will continue to rotate as it does now, the authors of the article say. True, this kind of rotation will not last forever; in the end, its own mass will make it move more evenly. According to the calculations of scientists, this "in the end" will come no earlier than in a billion years. More accurate estimates depend mainly on whether there is water ice in the asteroid (scientists failed to establish this).
When the collision happened that gave Ouamuamua a spin is difficult to say; it may have happened during the formation of the planets in the system where Oumuamua is from, or later, when he passed through the belt of rocky objects of the "native" planetary system. The first scenario is statistically more likely, however, to say for sure, you need to have high-quality photographs of the asteroid and judge by the craters left after the collisions. We do not have such images.