(55636) 2002 TX₃₀₀

(55636) 2002 TX₃₀₀
	2002 TX300 imaged by the Hubble Space Telescope on 16 September 2005
Discovery
Discovered by	NEAT (obs. code 644)
Discovery site	Palomar Obs.
Discovery date	15 October 2002
Designations
MPC designation	(55636) 2002 TX300
Alternative designations	2002 TX300
Minor planet category	TNO; classical (hot); Haumea family; distant; Scat-Ext;
Orbital characteristics (barycentric)
	Epoch 5 May 2025 (JD 2460800.5)
	Uncertainty parameter 0
Observation arc	70+ yr
Earliest precovery date	27 August 1954
Aphelion	48.587 AU
Perihelion	37.919 AU
Semi-major axis	43.253 AU
Eccentricity	0.1233
Orbital period (sidereal)	284.28 yr (103,832 d)
Mean anomaly	84.179°
Mean motion	0° 0m 12.482s / day
Inclination	25.853°
Longitude of ascending node	324.578°
Time of perihelion	≈ 24 June 2242
Argument of perihelion	340.302°
Known satellites	0
Physical characteristics
Mean diameter	320±50 km (2019); 323+95; −37 km (2018);
Mass	≈1.1×1019 kg (est. water ice density)
Mean density	≈1 g/cm3 (assumed water ice)
Sidereal rotation period	8.04±0.04 h (single-peaked); or 16.08±0.04 h (double-peaked);
Geometric albedo	0.65±0.15 (2019); 0.76+0.18; −0.45 (2018);
Temperature	49 K (subsolar)
Spectral type	BBb (neutral); B–V = 0.70±0.09; V–R = 0.36±0.02; V–I = 0.68±0.12;
Apparent magnitude	19 to 20
Absolute magnitude (H)	3.574±0.055; 3.50 (JPL);
Angular diameter	5 milliarcseconds

(55636) 2002 TX₃₀₀ (provisional designation 2002 TX₃₀₀) is an icy trans-Neptunian object orbiting the Sun in the Kuiper belt. It has a diameter of about 300 km (190 mi) and a highly reflective surface made of fresh water ice. It is the brightest and possibly the largest known member of the Haumea family, a population of Kuiper belt objects that broke off from the dwarf planet Haumea 4.4 billion years ago.

2002 TX₃₀₀ was discovered on 15 October 2002 by the NASA-directed Near-Earth Asteroid Tracking (NEAT) survey at Palomar Observatory. When it was discovered, astronomers initially inferred from its high brightness that it could be a large dwarf planet almost 1,000 km (620 mi) in diameter. This was later disproven in October 2009, when astronomers measured the diameter of 2002 TX₃₀₀ for the first time by observing the object occulting or blocking out the light of a background star. 2002 TX₃₀₀ is now known to be too small to likely qualify as a dwarf planet, and its brightness mainly comes from its reflective surface. 2002 TX₃₀₀ was the first Kuiper belt object (besides Pluto and its moon Charon) that was observed via stellar occultation.