An international team of astronomers has discovered an asteroid orbiting the Sun at roughly the same distance as Jupiter that appears to have originated from another solar system. The imaginatively named asteroid 2015 BZ509 could have immigrated to our little pocket of the universe from a neighboring stellar body billions of years ago, at a time when our Sun was still embedded in a colossal star cluster.

Asteroids are essentially the rocky remnants left over from the formation of our solar system some 4.6 billion years ago. They come in all shapes and sizes, from irregular bodies tens of feet in diameter, to (relatively) enormous bodies hundreds of miles wide, like Vesta, which was visited by NASA's Dawn spacecraft back in July 2011.

By studying these wandering chunks of leftover material, astronomers can attempt to unravel the mysteries surrounding the processes that created our solar system and subsequently sculpted it into the stunningly diverse, life-nourishing cosmic environment that we observe today.

Back in 2017, astronomers discovered the first alien asteroid to visit our solar system – the strange cigar-shaped celestial traveller `Oumuamua. Sadly, `Oumuamua wasn't here to stay, and instead barreled through our Sun's sphere of influence at a blistering 95,000 km/h (59,000 mph), fated to return to interstellar space.

New research published today in the Monthly Notices of the Royal Astronomical Society: Letters, has provided evidence for the theory that an unusual asteroid that shares roughly the same orbital region as the gas giant Jupiter is also likely of extra solar origin, and, unlike `Oumuamua, is in our solar system to stay.

The asteroid in question, 2015 BZ509, orbits the Sun in what is known as a retrograde orbit, meaning that it travels in the opposite direction to the body it is orbiting.

Hubble image of the stellar nursary NGC 604 – our Sun once formed in a cosmic cloud just like this in the ancient past, alongside countless other stars NASA / Hubble Heritage Team (AURA/STScI)

"How the asteroid came to move in this way while sharing Jupiter's orbit has until now been a mystery," explains Dr Fathi Namouni, lead author of the study, from the Observatoire de la Côte d'Azur, France. "If 2015 BZ509 were a native of our system, it should have had the same original direction as all of the other planets and asteroids, inherited from the cloud of gas and dust that formed them."

The team behind the new study used computer modeling to simulate the location of 2015 BZ509 all the way back to the end of our solar system's planetary formation era, some 4.5 billion years ago. The simulations revealed that the roughly 3-km-wide (1.9-mi) asteroid has essentially existed in its current Jovian orbit since the formation of the solar system.

According to the authors of the paper, the results indicate that 2015 BZ509 was a wandering asteroid that had been ejected from its birth system, and was subsequently captured roughly 4.5 billion years ago by the gravitational influence of our Sun. The findings also suggest that there could be more of these alien bodies accompanying the planets of our solar system in near-polar orbits.

2015 BZ509's cosmic immigration would likely have taken place back when our Sun was surrounded by a cluster of nearby stars, all of which had formed in the same stellar nursery. Each of those stars would have played host to its own solar system. In this scenario, 2015 BZ509 would have been ejected from its original home by the gravitational influence of planetary bodies.

The presence of an alien asteroid in a stable orbit a mere planetary hop skip and a jump from Earth is incredibly exciting news. Robotic pioneers could one day be sent to explore this chunk of ancient debris, and in so doing paint a picture of the formation of a distant solar system that coalesced around one of our Sun's stellar siblings.

The paper detailing the findings has been published in Monthly Notices of the Royal Astronomical Society: Letters.

Source: Royal Astronomical Society