For at least a million years, an asteroid orbiting the "wrong" way around the Sun has been playing a cosmic game of chicken to avoid collision with Jupiter and with about 6,000 other asteroids sharing the giant planet's space, a study says.
The findings published in the journal Nature showed that the orbit has been stable for at least a million years and will be stable for at least a million years more.
The asteroid, nicknamed Bee-Zed, is the only one in this solar system that is known both to have an opposite, retrograde orbit around the Sun while at the same time sharing a planet's orbital space, said researcher and co-author Paul Wiegert from University of Western Ontario in Canada.
Most of the known asteroids in our solar system travel around the Sun in what is called a prograde motion — that is, counter-clockwise when visualised from above.
But asteroid 2015 BZ509 ("Bee-Zed" for short) circles clockwise, in a retrograde motion — moving against the flow of all other asteroids in the giant planet's orbital entourage.
Put another way, it is as if Jupiter is a monster truck on a track circling the sun, and the asteroids in Jupiter's orbit are sub-compact cars all whizzing along in the same direction.
Bee-Zed is the rogue — driving around the track in the wrong direction — steering between the 6,000 other cars and swerving around the monster truck.
And it does so every single lap, and has done so for thousands of laps for a million years or more.
So how does it avoid colliding with Jupiter? Jupiter's gravity actually deflects the asteroid's path at each pass so as to allow both to continue safely on their way, Wiegert said.
Little is known about the asteroid, which was discovered in January, 2015. It has a diametre of about three kilometres and it may have originated from the same place as Halley's comet, which also has a retrograde orbit.
The team has not been able to determine yet if Bee-Zed is an icy comet or a rocky asteroid.
But their analysis — based on complex calculations and on observations through the Large Binocular Camera on the Large Binocular Telescope in Mt. Graham, Arizona, during a span of 300 days — show Bee-Zed is somehow able to maintain a stable orbit even as an outlier.
The researchers believe that learning more about the asteroid provides another intriguing glimpse into previously unknown and unmapped features of our solar system.
"The detective work has just begun," Wiegert said.