Astronomers have found nineteen interstellar asteroids orbiting the sun between Jupiter and Neptune. These asteroids previously belonged to a distant star system and have been orbiting our sun for approximately 4.5 billion years –the same time as the birth of our solar system.
It is believed that when the universe expanded, these asteroids were grabbed from their original star system and ended up staying in our own solar system because of the gravitational pull from our sun. “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 Fathi Namouni who is from the Observatoire de la Cote d’Azur in France and is the lead author of the study (which can be read in full here). “This enabled asteroids to be pulled from one star system to another.”
These interstellar asteroids are part of a group called Centaurs which has baffled scientists since the first one called Chiron was identified back in 1977. It has been suggested that these bodies were once part of the Kuiper Belt in the outer part of our solar system prior to travelling to the more interior region.
Dr. Namouni and co-author of the study Maria Helena Morais from the Universidade Estadual Paulista in Brazil performed computer simulations and found that billions of years ago the asteroids were orbiting the sun on a plane perpendicular to planetary motion. During that time when our solar system was forming, there was tons of debris floating around that would eventually form into Mercury, Venus, Earth, and Mars, but the interstellar asteroids were able to avoid the debris as they were orbiting at a further distance.
Dr. Morais went into further detail about this significant revelation, “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.” “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.”
This is such an incredible discovery as only two interstellar visitors have been previously discovered – ‘Oumuamua (which was found in October of 2017) and 2I/Borisov (noticed in August of 2019 but is now breaking apart).
With nineteen newly found interstellar asteroids, there are surely a bunch more hidden in our solar system, so the next question is ‘how many more?’