A new study has identified the first known permanent population of asteroids originating from outside our solar system. The objects are believed to have been captured from other stars billions of years ago, and have been orbiting our Sun in disguise ever since. The work is published in the journal Monthly Notices of the Royal Astronomical Society.
The first interstellar visitor, the asteroid known as ‘Oumuamua, hit the headlines in 2017, however it was just passing through. The newly-identified asteroids on the other hand are thought to have been present almost since the birth of our solar system, 4.5 billion years ago in a star cluster where each sun had its own planets and asteroids.
“The close proximity of the stars meant that they felt each other’s gravity much more strongly in those early days than they do today,” explained Dr. Fathi Namouni, lead author of the study. “This enabled asteroids to be pulled from one star system to another.”
In the new work, Dr. Namouni (Observatoire de la Cote d’Azur, France) and co-author Dr. Maria Helena Morais (Universidade Estadual Paulista, Brazil) ran numerical simulations to turn back the clock to the earliest days of the solar system, producing a snapshot that allowed them to see where the asteroids were originally located.
At the time of the snapshot, the asteroids were orbiting the Sun in a distant region beyond the reach of the original solar system disc, and also moving perpendicular to the orbital plane shared by the planets and other asteroids. These two observations indicate that the new group did not originally belong to our solar system, but must have been captured from the interstellar medium during planet formation.
Being able to tell apart interstellar asteroids from native asteroids born in the solar system has long eluded astronomers, but the team’s results identified 19 asteroids of interstellar origin. These are currently orbiting as part of the group of asteroids known as Centaurs, which roam the space in between the giant planets of the solar system.
“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 adds: “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.”
First asteroid population discovered from outside our Solar System
Paris, France (SPX) Apr 24 – Ka’epaoka’awela asteroid surprised the world in 2018: it was the first object in the solar system that was demonstrated to be of extrasolar origin. But now those who discovered it have announced that it is not alone.
Published in MNRAS on 23 April 2020, work by Fathi Namouni, a CNRS researcher in the Laboratoire Lagrange, and Helena Morais, researcher at UNESP in Brazil, proves that at least 19 other asteroids orbited another star before joining our system.
Although some interstellar bodies only pass through, others remain and orbit the Sun. This is the case for 19 asteroids that gravitate between Jupiter and Neptune. According to the two scientists’ calculations, their current orbits and characteristics can only be explained if these objects were not in our solar system at its birth, 4.5 billion years ago.
They are all part of the Centaur family, asteroids located between the gas giants that sometimes behave like comets, and whose orbits computer models cannot explain or predict. Fathi Namouni and Helena Morais chose to develop a very precise simulation of the orbits of these asteroids that “went back in time” to find their past positions.
The objects in our system already orbited the Sun 4.5 billion years ago in the same plane as the dust and gas disc in which they were formed. However, the 19 Centaurs were not part of this disc.
The simulations show not only that these Centaurs orbit the Sun on a plane perpendicular to planetary motion at that time, but also that they were located far from the disc that gave rise to solar system asteroids.
These 19 asteroids were not part of the solar system when it was born. Stellar proximity in the Sun’s birth cluster gave rise to strong gravitational interactions that allowed stellar systems to capture asteroids from one another. The scientists now plan to continue this work by looking for specific events when common capture of several extrasolar bodies occurred.