An interstellar asteroid has taken up "permanent residence" around the planet Jupiter, according to a new study of the asteroid 2015 BZ509. This is the first known interstellar object to be caught in one of the gravity wells of our solar system's planets, and the second interstellar object that we've seen in our solar system after the Oumuamua object passed by our sun in the fall of 2017.
Scientists do not know from which solar system the asteroid (referred to as BZ) came. According to the BBC, when Oumuamua came flying through in 2017 it was easy to pinpoint where it came from. The extra-solar object flew in a straight line, on a course that was not significantly affected by the gravity of the planets or the sun. BZ is locked into an unusual and distinctive orbit—and has been since the formation of the solar system—which renders any attempt at interstellar ballistics investigation useless. According to Dr Fathi Namouni from the Universite Cote d'Azur:
BZ reached the Solar System when it was forming, when the planets themselves were not exactly where they are now. So it's a little more tricky to figure out where it came from.
It was BZ's orbit that got scientists' attention in the first place. The asteroid was first discovered in 2015 and was remarkable for its retrograde orbit around the sun. That is, all of the planets and most of everything else in the solar system orbits the sun in one direction, BZ's orbit is in the opposite.
The asteroid seems to be in "orbital resonance with Jupiter, meaning that one year—one rotation around the sun—is exactly the same amount of time. This indicates that the asteroid was caught in Jupiter's orbit. Scientists say that this fact alone isn't proof of an interstellar origin but it is a "good hint."
That good hint prompted further investigation. Running complex computer simulations, Scientists turned back the clock in an attempt to find the location of both Jupiter and BZ at the time the asteroid was Shanghaied from its journey to who-knows-where. They were surprised at the results:
"We had this simulation which uses intense computing... to actually trace back in time to where this asteroid was when the planets finished forming.
Honestly we didn't have any idea what we were going to find. The last thing we expected... was that BZ has been in its current position most of the time."
According to Dr Namouni the results of the simulations proves that BZ is from another solar system, stating that it suggests there are no other plausible explanations.
There is much still to be learned about BZ509. Scientists don't yet know the composition of the asteroid, let alone where it came from, but they say studying it could offer valuable insight into the history of the solar system at large. According to the research team, because of this asteroid's orbital resonance with Jupiter, studying it may help us learn more about the largest planet's role in the formation of our solar system.
The first two interstellar objects in our solar system found within a year of each other. Could it be that our science is just getting better? If I were a betting man, I'd put my money on a lot more objects in our solar system having interstellar origins.