2015 FJ345

2015 FJ345 is a trans-Neptunian object and detached object, located in the scattered disc, the outermost region of the Solar System. It was first observed on 17 March 2015, by a team led by American astronomer Scott Sheppard at the Mauna Kea Observatories, Hawaii, United States. With its perihelion of almost 51 AU, it belongs to a small and poorly understood group of very distant objects with moderate eccentricities.[7][9] The object is not a dwarf planet candidate as it only measures approximately 120 kilometers (75 miles) in diameter.

2015 FJ345
Discovery [1]
Discovered byMauna Kea Obs.
Discovery siteMauna Kea Obs.
(first observed only)
Discovery date17 March 2015
Designations
2015 FJ345
Orbital characteristics [2]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter
Observation arc1.13 yr (413 d)
Aphelion74.837 AU
Perihelion50.785 AU
62.811 AU
Eccentricity0.1915
497.81 yr (181,824 d)
58.879°
0° 0m 7.2s / day
Inclination34.973°
37.881°
77.511°
Physical characteristics
Mean diameter
  • 0.08 (assumed)[6]
  • 0.09 (assumed)[5]
25.74[8]
7.9[1][2]

    Discovery and naming

    2015 FJ345 was first observed on 17 March 2015, by a team of astronomers led by Scott Sheppard of the Carnegie Institution for Science as part of the survey for distant solar system objects beyond the Kuiper Cliff using the new wide-field cameras on the Subaru and Cerro Tololo Inter-American Observatory (CTIO) telescopes.[7]

    Orbit and classification
    The object is located in the "gap", a poorly understood region.

    2015 FJ345 orbits the Sun at a distance of 50.8–74.8 AU once every 497 years and 10 months (181,824 days; semi-major axis of 62.81 AU). Its orbit has an eccentricity of 0.19 and an inclination of 35° with respect to the ecliptic.[2]

    The object belongs to the same group as 2004 XR190 ("Buffy"), 2014 FC72, 2014 FZ71 and 2015 KQ174 (also see diagram). With an orbital period of 498 years, it seems to be a resonant trans-Neptunian objects in a 1:3 resonance with Neptune,[7]:12 as several other objects,[5] but with a lower eccentricity (0.19 instead of more than 0.60) and higher perihelia (at 50.8 AU rather than 31–41 AU).

    Considered a scattered and detached object,[3][4][5] 2015 FJ345 is particularly unusual as it has an unusually circular orbit for a scattered-disc object (SDO). Although it is thought that traditional scattered-disc objects have been ejected into their current orbits by gravitational interactions with Neptune, the low eccentricity of its orbit and the distance of its perihelion (SDOs generally have highly eccentric orbits and perihelia less than 38 AU) seems hard to reconcile with such celestial mechanics. This has led to some uncertainty as to the current theoretical understanding of the outer Solar System. The theories include close stellar passages, unseen planet/rogue planets/planetary embryos in the early Kuiper belt, and resonance interaction with an outward-migrating Neptune. The Kozai mechanism is capable of transferring orbital eccentricity to a higher inclination.[9]

    Physical characteristics

    2015 FJ345 has a diameter estimated between 117 and 125 kilometers,[5][6][7] roughly a quarter the size of 2004 XR190 ("Buffy"), which is estimated at around 500 kilometres (310 mi), roughly a quarter the size of Pluto. It is therefore not a dwarf planet candidate.[6]

    References
    1. "2015 FJ345". Minor Planet Center. Retrieved 12 December 2018.
    2. "JPL Small-Body Database Browser: (2015 FJ345)" (2016-05-03 last obs.). Jet Propulsion Laboratory. Retrieved 12 December 2018.
    3. Jewitt, David, Morbidelli, Alessandro, & Rauer, Heike. (2007). Trans-Neptunian Objects and Comets: Saas-Fee Advanced Course 35. Swiss Society for Astrophysics and Astronomy. Berlin: Springer. ISBN 3-540-71957-1.
    4. Lykawka, Patryk Sofia; Mukai, Tadashi (July 2007). "Dynamical classification of trans-neptunian objects: Probing their origin, evolution, and interrelation". Icarus. 189 (1): 213–232. Bibcode:2007Icar..189..213L. doi:10.1016/j.icarus.2007.01.001.
    5. Johnston, Wm. Robert (7 October 2018). "List of Known Trans-Neptunian Objects". Johnston's Archive. Retrieved 12 December 2018.
    6. Brown, Michael E. "How many dwarf planets are there in the outer solar system?". California Institute of Technology. Retrieved 12 December 2018.
    7. Sheppard, Scott S.; Trujillo, Chadwick; Tholen, David J. (July 2016). "Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects with Moderate Semimajor Axes and Eccentricities". The Astrophysical Journal Letters. 825 (1): 7. arXiv:1606.02294. Bibcode:2016ApJ...825L..13S. doi:10.3847/2041-8205/825/1/L13. S2CID 118630570.
    8. "2015 FJ345 – Ephemerides". AstDyS-2, Asteroids – Dynamic Site, Department of Mathematics, University of Pisa, Italy. Retrieved 12 December 2018.
    9. Allen, R. L.; Gladman, B.; Kavelaars, J. J.; Petit, J.-M.; Parker, J. W.; Nicholson, P. (March 2006). "Discovery of a Low-Eccentricity, High-Inclination Kuiper Belt Object at 58 AU". The Astrophysical Journal. 640 (1): L83–L86. arXiv:astro-ph/0512430. Bibcode:2006ApJ...640L..83A. doi:10.1086/503098. S2CID 15588453. (Discovery paper)
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