Scientists came across an asteroid with an unusual orbit around the planet Jupiter in 2014, and now, using computer simulations, they have come up with a reason as to why it is maintaining that orbit.

An Interstellar Immigrant

2015 BZ509 is the first known asteroid from a different solar system to have been caught. It has been here in this system for a significant amount of time now. Scientists previously found another interstellar visitor in the solar system earlier this year with 'Oumuamua, however, that asteroid just passed by the solar system and kept going.  

2015 BZ509 first caught the attention of scientists when it was discovered in 2014 because of its retrograde orbit around Jupiter. A retrograde orbit occurs when objects move in the opposite direction. Scientists have discovered other objects with retrograde orbits but 2015 BZ509 has an elongated orbit that is out of alignment with those of the planets and other bodies.

The study is published in the journal Monthly Notices of the Royal Astronomical Society: Letters.

Tracing 2015 BZ509's Origin 

Scientists ran one million different simulations of 2015 BZ509's orbit, and each time the simulation had slightly different parameters. Objects with an eccentric orbit like 2015 BZ509's orbit are not stable for a long time. However, during the simulations, researchers did find a couple of stable orbits and that 2015 BZ509 is likely in one of the stable orbits.

While running the simulations, the scientists found that if these orbits were traced back in time, 2015 BZ509's orbit would go back to about 4.5 billion years ago. The solar system was still forming at that point. The asteroid 2015 BZ509 did not originate from this solar system and must have been caught in an orbit as it was passing through this solar system.

In the study, scientists say that there is no known mechanism that could have produced the asteroid in that orbit while the planets were still forming. They suggest that the asteroid was drifting through space until it was caught in the sun's gravity.

Scientists say that the reason for the asteroid being from another system is because of how the sun formed. It started from a tightly packed cluster of stars, where each star had its own system with planets and asteroids. This closeness let the gravity of each system attract, remove, and capture asteroids from another system.