title: A Uranian Trojan and the frequency of temporary giant-planet co-orbitals.
abstract: Trojan objects share a planet's orbit, never straying far from the triangular Lagrangian points, 60° ahead of (L4) or behind (L5) the planet. We report the detection of a Uranian Trojan; in our numerical integrations, 2011 QF99 oscillates around the Uranian L4 Lagrange point for >70,000 years and remains co-orbital for ~1 million years before becoming a Centaur. We constructed a Centaur model, supplied from the transneptunian region, to estimate temporary co-orbital capture frequency and duration (to a factor of 2 accuracy), finding that at any time 0.4 and 2.8% of the population will be Uranian and Neptunian co-orbitals, respectively. The co-orbital fraction (~2.4%) among Centaurs in the International Astronomical Union Minor Planet Centre database is thus as expected under transneptunian supply.
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada. mikea@astro.ubc.ca
authors.forename: Mike
authors.initials: M
authors.lastname: Alexandersen
authors.forename: Brett
authors.initials: B
authors.lastname: Gladman
authors.forename: Sarah
authors.initials: S
authors.lastname: Greenstreet
authors.forename: J J
authors.initials: JJ
authors.lastname: Kavelaars
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Petit
authors.forename: Stephen
authors.initials: S
authors.lastname: Gwyn