A bunch of asteroids whose exact origin is still unknown has been detected to be moving around the Sun in between the orbits of Jupiter and Neptune. Researchers from São Paulo State University’s Institute of Geosciences and Exact Sciences (IGCE-UNESP) have identified 19 space rocks of interstellar origin labeled as Centaurs, roaming the outer Solar System.
Professor Maria Helena Moreira Morais, one of the two co-authors, explained: “The Solar System formed 4.5 billion years ago in a stellar nursery, with its systems of planets and asteroids. The stars were close enough to each other to foster strong gravitational interactions that led to an exchange of material among the systems.”
Some cosmic bodies in the Solar System must, therefore, have taken shape around other stars, the Professor added. Until recently, though, astronomers couldn’t discern between captured interstellar objects and bodies that formed around the Sun.
“The first identification was made by us in 2018,” Professor Morais said.
Ka’epaoka’awela orbits the Sun in the direction opposite to that of the planets. Due to this, Ka’epaoka’awela is a retrograde co-orbital space rock of Jupiter. [Image: Haleakala Observatory]
The first identification to which the scientist referred to was the asteroid 514107 Ka’epaoka’awela, which was reported in 2018 by the São Paulo Research Foundation (FAPESP) in 2018. The name of the asteroid is Hawaiian and can be interpreted as ‘mischievous opposite-moving companion of Jupiter.’
The space rock has taken the path associated with the gas giant’s orbit for at least 4.5 billion years, but it orbits the Sun in the direction opposite to that of the planets. Due to this, Ka’epaoka’awela is a retrograde co-orbital space rock of Jupiter.
Professor Morais further explained: “When we identified it as an object that came from outside the Solar System, we didn’t know whether it was an isolated case or part of a vast population of immigrant asteroids. In this latest study, we recognized 19 Centaurs of interstellar origin.”
So Where Did They Actually Form?
Similar to Ka’epaoka’awela, the Centaurs detected in the new research have highly inclined orbits in correspondence to the orbital level of the planets. In order to find the origin of these objects, the team of researchers created a computer simulation that works like a time machine, following the asteroids’ trajectories back by 4.5 billion years.
This simulation helped scientists investigate where the objects were at that time. The planets and asteroids that formed in the Solar System emerged from a thin disk of gas and dust that once rotated around the Sun.
Because of this, they all traveled to the plane of the disk 4.5 billion years ago. Therefore, if the Centaurs took shape in the Solar System, they should also have moved in the plane of the disk back then.
“Our simulation showed that 4.5 billion years ago, these objects revolved around the Sun in orbits perpendicular to the disk’s plane. In addition, they did so in a region distant from the gravitational effects of the original disk,” Professor Morais said.
The findings showed that the Centaurs did not originally belong to our Solar System and must have appeared from nearby stars during the planetary formation period. This discovery is a major step in better learning about the differences and similarities between cosmic bodies that formed in the Solar System and objects in the system that were originally extrasolar.