Asteroid experts at São Paulo State University’s Institute of Geosciences and Exact Sciences have identified 19 space rocks of interstellar origin. The space rocks are classed as Centaurs – outer-Solar System objects orbiting between Jupiter and Neptune.
Professor Maria Helena Moreira Morais, one of the study’s co-authors, said: “The Solar System formed 4.5 billion years ago in a stellar nursery, with its systems of planets and asteroids.
Some objects now in the Solar System must therefore have formed around other stars
Professor Maria Helena Moreira Morais
“The stars were close enough to each other to foster strong gravitational interactions that led to an exchange of material among the systems.
“Some objects now in the Solar System must, therefore, have formed around other stars.
“Until recently, however, we couldn’t distinguish between captured interstellar objects and objects that formed around the Sun.
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“The first identification was made by us in 2018.”
The first identification to which Professor Morais referred was the asteroid 514107 Ka’epaoka’awela.
The Hawaiian name Ka’epaoka’awela translates as ‘mischievous opposite-moving companion of Jupiter’.
The rock has occupied the path corresponding to Jupiter’s orbit for at least 4.5 billion years but revolves around the Sun in the opposite direction to the planets.
Professor Morais said: “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 recognised 19 Centaurs of interstellar origin.”
The Centaurs identified in the study have highly inclined orbits with respect to the orbital plane of the planets.
Professor Morais added: “To investigate the origin of these objects, we built a computer simulation that works like a time machine, running their trajectories backwards by 4.5 billion years.
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“The simulation enabled us to find out where these objects were at that time.”
The planets and asteroids that originated in the Solar System emerged from a thin disk of gas and dust that once orbited the Sun.
For this reason, they all moved in the plane of the disk 4.5 billion years ago.
If the Centaurs originated in the solar system, they should also have moved in the plane of the disk at that time.
However, Professor Morais added: “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.
These two findings showed that the Centaurs did not originally belong to the Solar System and must have been captured from nearby stars during the period of planet formation.
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