Asteroids that share a planet”s orbit: the first retrograde co-orbital asteroid

Paul Wiegert (University of Western Ontario)

March 01, 2018

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Abstract: There are about 6000 asteroids which share Jupiter”s orbit around the Sun. Called the “Trojan asteroids”, they co-exist easily with this giant planet because they travel in the same direction as it, and remain roughly 60 degrees ahead of or behind it in its orbit. An as-yet-unnamed asteroid designated 2015 BZ509 is traveling in the opposite direction to Jupiter (and to all the planets in fact, as well as 99.99% of the other asteroids in our Solar System: a state referred to as “retrograde” motion) but is also safely sharing Jupiter”s orbital space. Asteroid 2015 BZ509 is trapped in a state dynamically analogous to that of the prograde Trojans. We will discuss the motion of this curious asteroid – listed #47 in Discover magazine”s Top 100 science stories of 2017 – and the other co-orbital bodies of our Solar System, examples which are now known for all planets except Mercury and Saturn.