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Asteroid 2011 QF99 is a minor planet from the outer Solar System and the first known Uranus trojan to be discovered. It measures approximately 60 kilometers in diameter, assuming an albedo of 0.05.[2][4] It was first observed 29 August 2011 during a deep survey of trans-Neptunian objects conducted with the Canada–France–Hawaii Telescope, but its identification as Uranian trojan was not announced until 2013.[2][5]

2011 QF99
Discovery siteMauna Kea Obs.
Discovery date29 August 2011[1]
(first observation only)
MPC designation2011 QF99
Uranus trojan[2]
centaur[1] · distant[3]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 3
Observation arc3.97 yr (1,449 days)
Aphelion22.422 AU
Perihelion15.659 AU
19.040 AU
83.08 yr (30,346 days)
0° 0m 42.84s / day
Physical characteristics
Dimensions60 km (calculated)[2]
0.05 (assumed)[2]
9.6 (R-band)[2]

2011 QF99 temporarily orbits near Uranus's L4 Lagrangian point (leading Uranus). It will continue to librate around L4 for at least 70,000 years and will remain a Uranus co-orbital for up to three million years before becoming a centaur. 2011 QF99 is thus a temporary Uranus trojan—a centaur captured some time ago.[2][6]

Uranus trojans are generally expected to be unstable and none of them are thought to be of primordial origin. A simulation led to the conclusion that at any given time, 0.4% of the centaurs in the scattered population within 34 AU would be Uranus co-orbitals, of which 64% (0.256% of all centaurs) would be in horseshoe orbits, 10% (0.04%) would be quasi-satellites, and 26% (0.104%) would be trojans (evenly split between the L4 and L5 groups).[2] A second Uranian Trojan, 2014 YX49, was announced in 2017.[7]


  1. ^ a b c d "JPL Small-Body Database Browser: (2011 QF99)" (2012-10-21 last obs.). Jet Propulsion Laboratory. Retrieved 12 October 2017.
  2. ^ a b c d e f g h Alexandersen, M.; Gladman, B.; Greenstreet, S.; Kavelaars, J. J.; Petit, J. -M.; Gwyn, S. (2013). "A Uranian Trojan and the Frequency of Temporary Giant-Planet Co-Orbitals" (PDF). Science. 341 (6149): 994–997. arXiv:1303.5774. Bibcode:2013Sci...341..994A. doi:10.1126/science.1238072. PMID 23990557.
  3. ^ "2011 QF99". Minor Planet Center. Retrieved 12 October 2017.
  4. ^ Choi, C. Q. (29 August 2013). "First 'Trojan' Asteroid Companion of Uranus Found". web site. TechMediaNetwork. Retrieved 3 September 2013.
  5. ^ Alexandersen, M.; Kavelaars, J.; Petit, J.; Gladman, B. (18 March 2013). "MPEC 2013-F19: 2011 QF99". IAU. Retrieved 3 September 2013.
  6. ^ de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (22 May 2014). "Comparative orbital evolution of transient Uranian co-orbitals: exploring the role of ephemeral multibody mean motion resonances". Monthly Notices of the Royal Astronomical Society. 441 (3): 2280–2295. arXiv:1404.2898. Bibcode:2014MNRAS.441.2280D. doi:10.1093/mnras/stu733.
  7. ^ de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (15 May 2017). "Asteroid 2014 YX49: a large transient Trojan of Uranus". Monthly Notices of the Royal Astronomical Society. 467 (2): 1561–1568. arXiv:1701.05541. Bibcode:2017MNRAS.467.1561D. doi:10.1093/mnras/stx197.

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