2013 FQ28
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2013 FQ28 orbits the Sun at a distance of 45.8–80.1 AU once every 499 years and 5 months (182,422 days; semi-major axis of 62.95 AU). Its orbit has an eccentricity of 0.27 and an inclination of 26° with respect to the ecliptic.[2]
With an orbital period of 499 years, and similar to 2015 FJ345, it seems to be a resonant trans-Neptunian objects in a 1:3 resonance with Neptune,[6]: 12 as several other objects,[5] but with a lower eccentricity (0.27 instead of more than 0.60) and a higher perihelia (at 45.8 AU rather than 31–41 AU).
Considered both a scattered and detached object,[3][4][5] 2013 FQ28 is particularly unusual as it has a relatively circular orbit for a scattered-disc object (SDO). Although it is thought that typical SDOs 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]
