(55636) 2002 TX300 is a bright Kuiper belt object in the outer Solar System estimated to be about 286 kilometres (178 mi) in diameter. It is a large member of the Haumea family that was discovered on October 15, 2002 by the Near-Earth Asteroid Tracking (NEAT) program.
2002 TX300 is a classical Kuiper belt object with an absolute magnitude between that of 50000 Quaoar and 20000 Varuna. 2002 TX300 has the most eccentric and inclined orbit of the three.
A variability of the visual brightness was also detected which could fit to 7.9 h or 15.8 h rotational period (the distinction between single or double-peaked curved could not be made with confidence). The changes in brightness are quite close to the error margin and could also be due to an irregular shape.
The diagrams to the left show polar and ecliptic views of the orbits of the two cubewanos. The perihelia (q) and the aphelia (Q) are marked with the dates of passage. The present positions (as of April 2006) are marked with the spheres, illustrating relative sizes and differences in albedo (both objects appear neutral in the visible spectrum).
(55636) 2002 TX300 is classified as a classical Kuiper belt object and follows an orbit very similar to that of Haumea: highly inclined (26°) and moderately eccentric (e ~0.12), far from Neptune’s perturbations (perihelion at ~37 AU). Other mid-sized cubewanos follow similar orbits as well, notably 2002 UX25 and 2002 AW197.
It has been observed 303 times, with precovery images back to 1954.
In 2004, the non-detection of IR thermal emissions put an upper limit of 709 kilometres (441 mi) on its diameter and a lower limit on the albedo of 0.19. In a 2006 International Astronomical Union press release discussing the IAU 2006 draft proposal, a diagram suggested that (55636) 2002 TX300 could be as large as 50000 Quaoar. The artist's diagram was largely based on the concept that (55636) 2002 TX300, with an absolute magnitude (H) of 3.4, may have an albedo around 0.08, which resulted in an overly optimistic diameter estimate of around 1,000 kilometres (620 mi).
In 2007, measurements by the Spitzer Space Telescope showed that it may be less than 641 kilometres (398 mi) in diameter. In 2008, it was considered to be a dwarf planet based on the its lightcurve amplitude and the assumption that it was larger than 450 kilometres (280 mi) in diameter. Because (55636) 2002 TX300 is a member of the Haumea family, it is assumed to have an albedo of around 0.7, which would result in a diameter of about 360 kilometres (220 mi).
(55636) 2002 TX300 occulted a relatively bright apparent magnitude 13.1 star in the constellation of Andromeda on October 9, 2009. This event was visible from Australia, possibly New Zealand, and the southern United States and Mexico. The RA and declination for this event was about 00 37 13.64 +28 22 23.2.: detailed information for observers was made available. The occultation produced a diameter of 286 kilometres (178 mi), suggesting an albedo of about 0.88. Somewhere between a size of 200 kilometres (120 mi) and 400 kilometres (250 mi), an icy body becomes rounded by its own gravity. With the exception of Neptune's moon Proteus, and possibly Eris's moon Dysnomia (whose shape is unknown), all icy moons with diameters 400 km or more are known to be spherical. Mike Brown lists it as a possible dwarf planet.
The spectrum in the visible and near-infrared rages is very similar to that of Charon, characterized by neutral to blue slope (1%/1000 Å) with deep (60%) water absorption bands at 1.5 and 2.0 μm). Mineralogical analysis indicates a substantial fraction of large ice (H2O) particles. The signal-to-noise ratio of the observations was insufficient to differentiate between amorphous or crystalline ice (crystalline ice was reported on Charon, Quaoar and Haumea). The proportion of highly processed organic materials (tholins), typically present on numerous trans-Neptunian objects, is very low. As suggested by Licandro et al. 2006, this lack of irradiated mantle suggest either a recent collision or comet activity.
Common physical characteristics with the dwarf planet Haumea together with similar orbit elements led to suggestion that (55636) 2002 TX300 was a member of the Haumean collisional family. The object, together with other members of the family ((19308) 1996 TO66, (24835) 1995 SM55, (120178) 2003 OP32 and (145453) 2005 RR43), would be created from ice mantle ejected from the proto-Haumea as result of a collision with another large (around 1,660 kilometres (1,030 mi)) body.