At the beginning of the Solar System, while violent collisions gave light to the planets from a disk of dust and rocks, a stranger from another system made him his new home. It was the asteroid that astronomers have named 2015 BZ509, the first object resident in our system that is discovered to have an interstellar origin.

2015 BZ509 takes 4.5 billion years orbiting the Sun at the same distance as Jupiter, in an unusual trajectory that can only be explained if it came from outside the Solar System, according to an investigation led by the Observatorio de la Costa Azul in Nice ( France) and published this week in the Monthly Magazine Notices of the Royal Astronomical Society: Letters

The unusual orbit of the asteroid can only be explained if it came from outside the Solar System

The orbit of this asteroid has intrigued astronomers since its discovery, in 2014, by the Pan-STARRS project of the Haleakala Observatory in Hawaii (United States). Around Jupiter and Saturn abound asteroids called centaurs, captured by the colossal gravitational influence of gaseous giants. Although some have bizarre orbits, the 2015 BZ509 is one of the strangest.

This asteroid moves in the opposite direction to most objects in the Solar System, including Jupiter. In addition, its orbit is inclined with respect to the ecliptic, which is the plane in which all the planets move.

To find out why such an unusual trajectory is involved, researchers have computer simulated the history of 2015 BZ509 and found that its orbit has remained the same for 4,500 million years, which is when the Solar System was formed.

At that time, the Sun was surrounded by a disc of dust and rocks in the rotation. All the material rotated in the same plane and in the same direction, which the planets and most asteroids inherited. If the 2015 BZ509 asteroid was born in the Solar System, at that time it should have been orbiting in the same plane. But it was not like that. “We did not expect it at all,” says Fathi Namouni, the researcher at the Costa Azul Observatory and director of the research. “The only way to explain this trajectory 4,500 million years ago is for BZ509 to be captured from the interstellar medium “, Add.

Although it is not the first interstellar asteroid discovered – the title took it last year ‘Oumuamua – the finding creates new possibilities in the solar system’s formation models, according to the researchers. “It opens the door to an exchange of materials with other planetary systems that are in relative proximity to our galactic environment,” agrees Josep Maria Trigo, a researcher at the Institute of Science of the Space (IEEC-CSIC), who has not participated in the investigation. “Once we know its chemical composition, we could determine if similar asteroids brought water to Earth,” says Fathi Namouni.

The origin of the asteroid is still a mystery, but astronomers think it could have moved into our system shortly after the birth of the Sun, which formed in a cluster along with other stars, “where each star had its own system of planets and asteroids” , Helena Morais, of the Paulista State University in Rio Claro (Brazil), co-author of the study, explained in a statement. “The proximity of the stars and the gravitational forces of the planets helped the systems attract and capture asteroids from each other.”

It opens the door to an exchange of materials with other planetary systems that are in relative proximity to our galactic environment

And is that 2015 BZ509 may not be the only outsider who migrated to the Solar System in its infancy. The researchers now point to a group of asteroids outside of Neptune’s orbit whose orbits are perpendicular to the ecliptic. Their next goal is to study them to determine if they also come from a foreign system, explains Fathi Namouni.