‘Oumuamua Might Not Have Been The Only Interstellar Asteroid We Have Seen

A swarm of asteroids in front of the Milky Way galaxy (3D illustration, elements of this image are furnished by NASA). Dotted Yeti/Shutterstock

‘Oumuamua is the first interstellar asteroid we have seen pass through the the inner solar system. While this curious object came and went in late 2017, a new study suggests there may be a permanent population of interstellar asteroids among other minor planets in the solar system.

As reported in the Monthly Notices of the Royal Astronomical Society, astronomers believe they have found a population of asteroids in the solar system that were stolen from another star. There are 19 of these interstellar objects, 17 of which belong to a group of asteroids called the Centaurs, which orbit between the giant planets of the solar system, and two from beyond the orbit of Neptune.

All 19 objects have a high inclination with respect to the orbital plane of the solar system where the planets more or less reside. When Dr Fathi Namouni and Dr Maria Helena Morais ran a simulation, they found that the asteroids did not reach their orbits by lifting themselves above the orbital plane, but were orbiting much further out than the planets and in a polar orbit, close to 90 degrees from the rest of the objects in the solar system. These two facts suggest they did not form with the other planets, comets, and asteroids; instead, they may have been snatched from another star when the Sun and the solar system where still within the stellar nursery from which they formed. For this to occur, they likely had close star neighbors.

“The close proximity of the stars meant that they felt each others’ gravity much more strongly in those early days than they do today,” lead author Dr Namouni, from the Observatoire de la Côte d'Azur, said in a statement. “This enabled asteroids to be pulled from one star system to another.”

If these objects formed around another star, they are of immense scientific value. Their similarities and differences with asteroids that formed in the solar system might tell us more about where the Sun came from.

“The discovery of a whole population of asteroids of interstellar origin is an important step in understanding the physical and chemical similarities and differences between Solar System-born and interstellar asteroids,” commented Dr Morais.

She added: “This population will give us clues about the Sun’s early birth cluster, how interstellar asteroid capture occurred, and the role that interstellar matter had in chemically enriching the Solar System and shaping its evolution.”

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