2001 QR322

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2001 QR322
Discovered by Deep Ecliptic Survey
Discovery date 21 August 2001[1]
Alternative names MPO157352
Minor planet category Trojan asteroid
Orbital characteristics[1][2]
Epoch 2011-Aug-27.0 (JD 2455800.5)
Aphelion 31.326 AU
Perihelion 29.468 AU
Semi-major axis 30.397 AU
Eccentricity 0.0306
Orbital period 167.59 yr (61212 d)
Mean anomaly 56.8°
Inclination 1.3213°
Longitude of ascending node 151.55°
Argument of perihelion 168.1°
Physical characteristics
Dimensions 60–160 km[3]
Absolute magnitude (H) 8.2

2001 QR322 (also written 2001 QR322) was the first Neptune trojan discovered, in 2001 by the Deep Ecliptic Survey. It orbits ahead of Neptune at its L4 Lagrangian point.[2][4]

With an absolute magnitude of 7.8[1] to 8.2,[2] it has a diameter in the range of 60 to 160 km.[3]

Other Neptune trojans have been discovered since. A study by Scott S. Sheppard and Chad Trujillo from the Carnegie Institution suggests that Neptune could possibly have twenty times more trojans than Jupiter.[5]

Dynamical stability[edit]

Early studies of the dynamical stability of 2001 QR322, which used a small number of test particles spread over the uncertainties of just a few orbital parameters that were derived from a limited observation arc, suggested that 2001 QR322 is on a remarkably stable orbit, because most test particles remained on trojan orbits for 5 Gyr.[6] Thereafter, the stability of Neptune trojans was simply assumed.[6]

A more recent study, which used a very large number of test particles spread over the 3σ uncertainties in all six orbital parameters derived from a longer observational arc, has indicated that 2001 QR322 is far less dynamically stable than previously thought.[6] The test particles were lost exponentially with a half life of 553 Myr.[6] Further observations can determine whether 2001 QR322's orbit is actually within the dynamically stable or within the unstable part.[6]

The stability is strongly dependent on semi-major axis, with a≥30.30 AU being far less stable, but only very weakly dependent on the other orbital parameters.[6] This is because those with larger semi-major axes have larger libration amplitudes, with amplitudes ~70° and above being destabilized by secondary resonances between the trojan motion and the dynamics of at least Saturn, Uranus, and Neptune.[6] Secular resonances were found not to contribute to the dynamical stability of 2001 QR322.[6]


  1. ^ a b c "JPL Small-Body Database Browser: (2001 QR322)". 2008-07-21 last obs. Retrieved 2009-09-04. 
  2. ^ a b c "List Of Neptune Trojans". Minor Planet Center. Retrieved 2011-05-08. 
  3. ^ a b "Absolute Magnitude (H)". Archived from the original on 14 May 2008. Retrieved 2008-05-08. 
  4. ^ Marc W. Buie (2008-07-21 using 26 of 26 observations). "Orbit Fit and Astrometric record for 01QR322". SwRI (Space Science Department). Retrieved 2009-09-03. 
  5. ^ "Neptune May Have Thousands of Escorts". Space.com. 30 January 2007. Retrieved 2009-09-04. 
  6. ^ a b c d e f g h Horner, J.; Lykawka, P. S. (June 2010). "2001 QR322: a dynamically unstable Neptune Trojan?" (pdf). Monthly Notices of the Royal Astronomical Society 405 (1): 49–56. arXiv:1002.4699. Bibcode:2010MNRAS.405...49H. doi:10.1111/j.1365-2966.2010.16441.x. Retrieved 2012-03-20. 

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