2001 QR322

2001 QR322 is a minor planet and the first Neptune trojan discovered on 21 August 2001, by the Deep Ecliptic Survey at Cerro Tololo Observatory in Chile.[2][6] It orbits ahead of Neptune at its L4 Lagrangian point.[3]

2001 QR322
Discovery [1][2]
Discovered byDES
Discovery siteCerro Tololo Obs.
Discovery date21 August 2001
(discovery: first observation only)
Designations
2001 QR322
Neptune trojan · L4 [3]
centaur [1] · distant [2]
Orbital characteristics [1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 3
Observation arc12.26 yr (4,479 days)
Aphelion30.968 AU
Perihelion29.262 AU
30.115 AU
Eccentricity0.0283
165.27 yr (60,363 days)
86.551°
0° 0m 21.6s / day
Inclination1.3250°
151.75°
151.11°
Physical characteristics
Dimensions110 km (est. at 0.10)[4]
140 km[5]
22.5[5]
7.9[1][3]

    Other Neptune trojans have been discovered since. A study by American astronomers Scott Sheppard and Chad Trujillo from the Carnegie Institution suggests that Neptune could possibly have twenty times more trojans than Jupiter.[7]

    Diameter

    The discoverers estimate that the body has a mean-diameter of 140 kilometers based on a magnitude of 22.5.[5] Based on a generic magnitude-to-diameter conversion, it measures approximately 110 kilometers in diameter using an absolute magnitude of 7.9 and an assumed albedo of 0.10.[4]

    Orbit

    2001 QR322 orbits the Sun with a semi-major axis of 30.115 AU at a distance of 29.3–31.0 AU once every 165 years and 3 months (60,363 days). Its orbit has an eccentricity of 0.03 and an inclination of 1° with respect to the ecliptic.[1]

    Dynamical stability

    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. Thereafter, the stability of Neptune trojans was simply assumed.[8]

    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. The test particles were lost exponentially with a half life of 553 Myr. Further observations can determine whether 2001 QR322's orbit is actually within the dynamically stable or within the unstable part.[8]

    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. 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. Secular resonances were found not to contribute to the dynamical stability of 2001 QR322.[8]

    Numbering and naming

    Due to its orbital uncertainty, this minor planet has not been numbered and its official discoverers have not been determined.[1][2] If named, it will follow the naming scheme already established with 385571 Otrera, which is to name these objects after figures related to the Amazons, an all-female warrior tribe that fought in the Trojan War on the side of the Trojans against the Greek.[9]

    References
    1. "JPL Small-Body Database Browser: (2001 QR322)" (2013-11-25 last obs.). Jet Propulsion Laboratory. Retrieved 5 August 2017.
    2. "2001 QR322". Minor Planet Center. Retrieved 5 August 2017.
    3. "List Of Neptune Trojans". Minor Planet Center. 10 July 2017. Retrieved 4 August 2017.
    4. "Asteroid Size Estimator". CNEOS/JPL. Retrieved 2 August 2017.
    5. Lakdawalla, Emily (13 August 2010). "2008 LC15, the first Trojan asteroid discovered in Neptune's L5 point". The Planetary Society. Retrieved 4 August 2017.
    6. Marc W. Buie. "Orbit Fit and Astrometric record for 01QR322" (2008-07-21 using 26 of 26 observations). SwRI (Space Science Department). Retrieved 3 September 2009.
    7. "Neptune May Have Thousands of Escorts". Space.com. 30 January 2007. Retrieved 4 September 2009.
    8. Horner, J.; Lykawka, P. S. (June 2010). "2001 QR322: a dynamically unstable Neptune Trojan?". 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.
    9. Ticha, J.; et al. (10 April 2018). "DIVISION F / Working Group for Small Body Nomenclature Working Group for Small Body Nomenclature. THE TRIENNIAL REPORT (2015 Sept 1 - 2018 Feb 15)" (PDF). IAU. Retrieved 25 August 2018.

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