Astronomers discover 'tag-along' Trojan asteroid following Uranus

Canadian astronomers report they've discovered the first Trojan asteroid -- a class of asteroids that share orbits with planets -- in the orbit of Uranus. Researchers at the University of British Columbia said they believe the asteroid 2011 QF99 is part of a larger-than-expected population of transient objects temporarily trapped by the gravitational pull of the Solar System's giant planets. Astronomers had considered Trojans at Uranus unlikely because the gravitational pull of larger neighboring planets would eventually destabilize and expel any Uranian Trojans. QF99 is a temporary Trojan, the Canadian astronomers said, only recently (within the last few hundred thousand years) captured by Uranus and likely to escape the planet's gravitational pull in about a million years. "Surprisingly, our model predicts that at any given time three per cent of scattered objects between Jupiter and Neptune should be co-orbitals of Uranus or Neptune," lead study author Mike Alexandersen said. This percentage had never before been computed and is much higher than previous estimates, a UBC release said Wednesday. "This tells us something about the current evolution of the Solar System," Alexandersen said. "By studying the process by which Trojans become temporarily captured, one can better understand how objects migrate into the planetary region of the Solar System."