Pan-STARRS Says It Just Found an Ancient Interstellar Asteroid Near Jupiter
Last year, the weird, needle-shaped interstellar asteroid Oumuamua zoomed through our solar system, marking the first time we've had a chance to observe a visitor from another solar system.
Oumuamua sparked a frenzy of speculation about what it was (interstellar rock or alien spaceship?), where it came from, and why it was sailing through space at 196,000 miles per hour, but according to a new study, we've had another foreign asteroid right under our noses for years without knowing it.
For 4.5 billion years, in fact.
The asteroid, named 2015 BZ509, was first spotted in 2014, coincidentally by Pan-STARRS, the same Hawaii-based organization that first identified Oumuamua.
What tipped researchers off to the fact that 2015 BZ509 might be something special was that it was orbiting Jupiter in reverse.
Almost everything in our solar orbits in the same direction (calling it clockwise or counter-clockwise is a matter of perspective), but 2015 BZ509 goes the opposite direction, which raises some interesting questions about its origins. According to Fathi Namouni, Côte d'Azur Observatory, one of the authors of a new study investigating the asteroid:
"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."
2015 BZ509 wasn't here when our solar system formed, but it has been here for a long, long time according to Helena Morais, another author of the study:
"We showed that 2015 BZ509 has been a retrograde co-orbital of Jupiter over the age of the solar system, i.e., since 4.5 billion years ago. The solar system could not produce retrograde orbits so far back in time, so the only option left is that of capture from another system."
It's not clear where the asteroid came from, but like Oumuamua it could provide clues to what its home solar system looks like, as well as that star system's history—sort of like a giant, rocky postcard from another place and time.