At least 19 asteroids orbited another, distant alien star before joining our solar system drifting between Jupiter and Neptune. According to the calculations of the two scientists, the asteroids’ current orbits and characteristics can only be explained if these objects were not in our solar system when it was created, around 4.5 billion years ago.

The study describing the alien asteroids and their origin was published in Monthly Notices of the Royal Astronomical Society. The study was presented by Fathi Namouni, a researcher at the Laboratoire Lagrange (CNRS / Observatoire de la Côte d’Azur / Université Côte d’Azur), and Helena Morais, a researcher at UNESP in Brazil.

According to the researchers, these asteroids belong to the Centaur family of asteroids. Centaur asteroids are cosmic bodies that resemble asteroids in size, but comets in composition, orbiting the sun in odd orbits between Jupiter and Neptune. The first Centaur asteroid–designated Chiron–was found by astronomers in 1977. Hundreds of Centaurs exist, an astronomer theorizes that many thousands more drift around the planets of our solar system, waiting to be discovered and cataloged.

To understand more about centaurs and their origin, Fathi Namouni, and Helena Morais decided to develop a very precise simulation of the orbits of these asteroids that essentially allowed them to “go back in time” in order to discover the origins of the asteroids and their evolution in the solar system. Cosmic objects in our system already orbited the sun 4.5 billion years ago in the same plane as the dust and gas disk in which they formed.

However, the 19 centaurs were not part of this cosmic collection. The simulations not only show that these centaurs orbit the sun in a plane perpendicular to planetary motion at the time, but it also indicates that they were positioned far from the disk that gave rise to asteroids in the solar system, reports CNRS.

This has led the scientists to suggest that the 19 asteroids were not part of the solar system when it was born. The stellar proximity in the sun’s birth cluster gave rise to strong gravitational interactions that allowed star systems to capture asteroids from each other. Scientists now plan to continue this work looking for specific events when the common capture of various extrasolar bodies occurred.

“The statistical distributions show that their orbits were nearly polar 4.5 Gyr (Gyr means billion years) in the past, and were located in the scattered disc and inner Oort cloud regions. Early polar inclinations cannot be accounted for by current Solar system formation theory as the early planetesimal system must have been nearly flat in order to explain the low-inclination asteroid and Kuiper belts,” the researchers explained.

“The nearly polar orbits of high-inclination Centaurs 4.5 Gyr in the past, therefore, indicate their probable early capture from the interstellar medium.”

Centaurs, some of which are as large as about 250 km (160 miles) in diameter, are believed to have originated past the orbits of Neptune and Pluto, in a vast, disk-shaped repository of comet nuclei called the Kuiper belt, one of the outermost regions in our solar system.