There are 19 interstellar asteroids between Jupiter and Neptune ⁠— and even computers can’t predict where they are headed

A stellar nursery in the Lobster Nebula (NGC6357), where star systems exchange asteroids as our Solar System is thought to have done 4.5 billion years agoESO / VVV Survey / D. Minniti


  • Oumuamua and Borisov weren’t the first interstellar asteroids to visit our solar system.
  • Scientists have discovered 19 news asteroids hiding in the space between Neptune and Jupiter.
  • These 19 asteroids from the Centaur family orbit the Sun on a plane that was perpendicular to planetary motion 4.5 billion years ago.
Interstellar asteroids — asteroids from outside our solar system — may not be as rare as we once thought they were. An entire population was discovered between Jupiter and Neptune.

The Centaur family of asteroids roam the space between the two gas giants but even computer models can’t predict where they’ll be headed next.

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The Centaurs in the study have so far not been imaged directly. Their sizes range from 10km to 300km, and small Centaurs may look like the 53km asteroid Mathilde imaged by NASA’s NEAR Shoemaker mission in 1997NASA / NEAR Shoemaker.

“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,” said Maria Helena Morais, one of the authors of the discovery published in the Monthly Notices of the Royal Astronomical Society.

The general consensus in the scientific community is that interstellar asteroids are rare and visit the neck of the solar system every couple of years as they pass through. Other than that, we have the asteroid belt, which stretches from Mars to Jupiter.

This also means that Oumuamua wasn’t the first interstellar visit and neither was Borisov. The Centaur asteroids have been around since the birth of our solar system — even though they themselves were born in other star systems.
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The origin story of Centaur asteroids
These 19 new asteroids from the Centaur family could have originated outside the solar system, according to calculations. The researchers claim that there’s no other plausible explanation for their orbits and characteristics.

The simulations show that these Centaurs orbit the Sun on a plane that was perpendicular to planetary motion at that time. They also imply that the asteroids were located far from the disc that gave rise to our own solar system’s asteroids.

Illustration of the orbit of a Centaur asteroid 4.5 billion years ago, relative to the protoplanetary disc. The asteroid orbits around the sun far from the disc in a plane perpendicular to it.Protoplanetary disc/NASA

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“The close proximity of the stars meant that they felt each others’ gravity much more strongly in those early days than they do today. This enabled asteroids to be pulled from one star system to another,” explained Fathi Namouni, lead author of the study.

When our own solar system was born, 4.5 billion years ago, the Centaurs got caught in its gravity and have been orbiting our Sun in incognito mode ever since.

On the hunt for other interstellar asteroids that may have been hiding in plain sight

The ability to differentiate between interstellar asteroids and native asteroids has eluded astronomers for a long time.
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“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,” said Namouni.

The scientists now plan to continue this work by looking for specific events when common capture of several extrasolar bodies occurred.

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