An asteroid orbiting backwards around the Sun likely originated in another solar system, according to astronomers from the University Cote d’Azur in France. The movement of this enigmatic object could shed light on the ancient history of the Solar System.
The asteroid 2015 BZ509 revolves around the Sun in a direction opposite to that of all eight planets in our solar system. Computer simulations suggest the two-mile wide object has always maintained a similar orbit around our parent star. This provides significant evidence it originally formed around an alien star.
“How the asteroid came to move in this way while sharing Jupiter’s orbit has until now been a mystery. 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,” said Fathi Namouni of the University Cote d’Azur.
Simulations suggest the object likely arrived in our solar system roughly 4.5 billion years ago, as the planets in our solar family, including Earth, were being formed. Astronomers believe stars, including the Sun, formed in closely-packed clusters, which would explain how such an interstellar interloper may have entered our planetary family.
In 2017, astronomers spotted another interstellar interloper passing through our solar system. However, that object, known as Oumuamua, quickly passed our family of planets, never entering a stable orbit around the Sun.
This finding could help shed light on the nature of the earliest days of our solar system, as well as the chemical makeup of the space around Earth which led to life.
If this discovery is confirmed, asteroid 2015 BZ509 will be the first object from outside the solar system known to have established permanent residence among our own stellar family.