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Key takeaways

  • Astronomers have identified 19 asteroids in our Solar System that likely originated from other star systems.
  • These asteroids were probably captured by the Sun’s gravity when it was part of a star cluster over 4.5 billion years ago.
  • The identified asteroids have unusual orbits, some moving in the opposite direction to the planets, indicating their interstellar origin.
  • Researchers used simulations to trace the orbits of these asteroids back to the Solar System’s early days, revealing their extra-solar origins.
  • Studying these asteroids can provide valuable information about the Solar System’s formation, the early star cluster environment, and interstellar matter’s influence.

The solar system has been around for a long time. So, when ‘Oumuamua was discovered in 2017, it was fairly certain that it wasn’t the only object from interstellar space to visit us in the 4.57 billion-year history. Then comet 2I/Borisov appeared last year. This very much sealed the deal.

But where are the remainder of our interplanetary visitors? We’ll undoubtedly see a few more fly in from the wild in the following years. According to recent study, a large number of interstellar asteroids have spent a lengthy period in the Solar System.

Based on how they orbit the Sun, a team of academics has found 19 asteroids that they believe were taken from another star when the Solar System was only a few million years old.

Astronomers believe that the Sun was once part of a stellar nursery, which is a cluster of stars produced from the same cloud of gas and dust.

“The close proximity of the stars meant that they felt each others’ gravity much more strongly in those early days than they do today,” stated astronomer and cosmologist Fathi Namouni of the Observatoire de la Côte d’Azur in France.

“This enabled asteroids to be pulled from one star system to another.”

Fathi and his colleague, astronomer Helena Morais of Brazil’s Universidade Estadual Paulista, discovered their first permanent interstellar dweller in 2018. They were investigating into the Centaurs, a group of asteroids that orbit between Jupiter and Neptune and frequently have bizarre orbits.

The asteroid 2015 BZ509, also known as Kaʻepaokaʻawela, had a unique orbit that was identical to Jupiter’s, but in the other direction (retrograde). If it was native to the Solar System, it should have traveled in the same direction as everything else, thus the researchers conducted simulations to determine its origins.

Kaʻepaokaʻawela presumably originated in interstellar space and was taken into the Solar System some 4.5 billion years ago.

In the current study, the scientists looked at Centaurs and trans-Neptunian objects with a high orbital inclination relative to the planets’ orbital plane, which can put them near to a polar orbit. Several of these objects, including Kaʻepaokaʻawela, have retrograde orbits.

“With moderate to high eccentricities, Centaurs’ orbits may be inclined by a few degrees with respect to the Solar System’s invariable plane to almost 180° resulting in retrograde motion,” according to the study’s authors.

“Their orbital properties are frequently interpreted as evidence of their tumultuous past in the Solar System, a perception supported by their so-called instability. If a Centaur orbit is integrated forward or backward in time, it will always strike the Sun, the planets, or be thrown from the Solar System.

The survey includes 17 Centaurs with orbital inclinations more than 60 degrees, as well as two objects that orbit past Neptune, known as trans-Neptunian objects. The researchers utilized the known orbits of these objects to make numerous clones of each, simulating their orbits back in time to 4.5 billion years ago.

At the time, everything in our Solar System was more or less in a flat disc around the Sun, leftover from the young star’s accretion disk. It should all have been circling in the same plane and direction.

However, according to the team’s models, these 19 asteroids were not part of that neat disk. Most of the clones did end up colliding with the Sun or being thrown out of the Solar System. Fewer ended up crashing onto a planet. Fewer asteroids maintained stable orbits, but those that exist today must have beaten the odds, according to the model.

However, those that did reach a stable orbit did not begin in the Sun’s disk. Not only did they extend well beyond the disc’s fringes, but their orbits were perpendicular to it.

According to the researchers, the likelihood that the asteroids were grabbed by the Sun’s gravity from outside the Solar System is greater than the likelihood that they were formed here, along with the rest of the Solar System’s rocks, from the Sun’s leftovers.

Future research into these rocks might help corroborate the team’s results; from there, they could help us detect other interstellar interlopers, allowing us to understand more about the creation of the Solar System and other planetary systems.

“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,” Morais told the newspaper.

“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.”

The research has been published in the Monthly Notices of the Royal Astronomical Society.

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