(532037) 2013 FY27

(532037) 2013 FY₂₇ (provisional designation 2013 FY₂₇) is a large trans-Neptunian object in the scattered disc.^[7] It was discovered on 31 March 2014 by Scott Sheppard and Chad Trujillo at Cerro Tololo Observatory in Chile.^[1] With a nominal diameter of about 740 km (460 mi), 2013 FY₂₇ is large enough that some astronomers consider it a possible dwarf planet. It is estimated to be the largest unnamed Solar System object with a measured diameter, though uncertainties in the measurements mean that several others could actually be larger. 2013 FY₂₇ has one unnamed moon about 190 kilometres (120 mi) in diameter.

(532037) 2013 FY₂₇

2013 FY27 and its satellite, imaged by the Hubble Space Telescope on 15 January 2018
Discovery[1]
Discovered by	Scott Sheppard Chad Trujillo (obs. 807)
Discovery date	17 March 2013 (announced on 31 March 2014)
Designations
MPC designation	2013 FY27
Minor planet category	TNO SDO[citation needed]
Orbital characteristics[2]
Epoch 2023 Feb 25 (JD 2460000.5)
Uncertainty parameter 4
Observation arc	3953 days (10.82 yr)
Earliest precovery date	15 March 2011 (Pan-STARRS)
Aphelion	81.912 AU (12.2539 Tm)
Perihelion	35.199 AU (5.2657 Tm)
Semi-major axis	58.555 AU (8.7597 Tm)
Eccentricity	0.3989
Orbital period (sidereal)	448.08 yr (163,660 d)
Mean anomaly	215.947°
Mean motion	0° 0m 7.92s /day
Inclination	33.290°
Longitude of ascending node	186.922°
Time of perihelion	≈ 2202 June 15 ± 17 days
Argument of perihelion	139.752°
Known satellites	1[3][4][5]
Physical characteristics
Mean diameter	765+80 −85 km (effective diameter)[3] 742+78 −83 km (primary)[a][3]
Geometric albedo	0.170+0.045 −0.030[3]
Temperature	22 K (perihelion) to 16 K (aphelion)
Spectral type	moderately red V–R = 0.56±0.03 R–I = 0.52±0.03[3]
Apparent magnitude	22.5[6]
Absolute magnitude (H)	3.15±0.03[3][2]

Orbit

Orbit of 2013 FY₂₇

2013 FY₂₇ orbits the Sun once every 449 years. It will come to perihelion around November 2202,^[2][b] at a distance of about 35.6 AU. It is currently near aphelion, 80 AU from the Sun, and, as a result, it has an apparent magnitude of 22.^[1] Its orbit has a significant inclination of 33°.^[2] The sednoid 2012 VP113 and the scattered-disc object 2013 FZ27 were discovered by the same survey as 2013 FY₂₇ and were announced within about a week of one another.

Physical properties

2013 FY₂₇ has a diameter of about 740 kilometres (460 mi), placing it at a transition zone between medium-sized and large TNOs. Using the Atacama Large Millimeter Array and Magellan Telescopes, its albedo was found to be 0.17, and its colour to be moderately red. 2013 FY₂₇ has an absolute magnitude (H) of 3.2,^[2] making it the ninth-intrinsically-brightest known trans-Neptunian system.^[8]

The brightness of 2013 FY₂₇ varies by less than 0.06 mag over hours and days, suggesting that it either has a very long rotation period, an approximately spheroidal shape, or a rotation axis pointing towards Earth.^[3]

2013 FY₂₇ is a possible dwarf planet, though not a likely one. Grundy et al. calculate that bodies less than about 1000 km in diameter, with albedos less than ≈0.2 and densities less than ≈1.2 g/cm³, may retain a degree of porosity in their physical structure, having never collapsed into fully solid bodies, and therefore could not be dwarf planets.^[9] However, the albedo of 2013 FY₂₇ may be around that limit, and there is no way to estimate its density.

Satellite

Satellite

Animation of 2013 FY27 and its satellite, imaged by the Hubble Space Telescope from January to July 2018
Discovery[3]
Discovered by	Scott Sheppard Yanga R. Fernández Arielle Moullet
Discovery date	15 January 2018
Orbital characteristics[3]
Semi-major axis	>9800±40 km
Orbital period (sidereal)	≈19 d (for assumed density 1.6 g/cm3)[10]
Satellite of	2013 FY27
Physical characteristics
Mean diameter	≈186 km (assuming equal albedos)[3]
Albedo	0.170+0.045 −0.030 (assumed)
Apparent magnitude	25.5[6]
Absolute magnitude (H)	6.15[c]

Using Hubble Space Telescope observations taken in January 2018, Scott Sheppard found a satellite around 2013 FY₂₇, that was 0.17 arcseconds away and 3.0±0.2 mag fainter than its primary. The discovery was announced on 10 August 2018.^[11] The satellite does not have a provisional designation nor a proper name.^[2] Assuming the two components have equal albedos, they are about 742+78
−83 km and 186±20 km in diameter, respectively.^[3] Follow-up observations were taken between May and July 2018 in order to determine the orbit of the satellite,^[4] but the results of these observations remain yet to be published as of 2022^[update].^[6] Once the orbit is known, the mass of the system can be determined.

See also

• List of Solar System objects most distant from the Sun
• List of Solar System objects by size

Notes

1. Assuming the two components have equal albedos
2. The uncertainty in the time of perihelion passage is ≈1 month (1-sigma) or 3.6 months (3-sigma).^[2]
3. Given the primary's absolute magnitude of H = 3.15 and a magnitude difference of Δm = 3.00 between the primary and satellite, the sum of those magnitudes is the satellite's absolute magnitude, 6.15.^[3][6]