# (84522) 2002 TC302

(84522) 2002 TC$_{302}$ (provisional designation 2002 TC$_{302}$) is a mid-sized trans-Neptunian object located in the outermost region of the Solar System. It was discovered on 9 October 2002, by American astronomers Mike Brown, Chad Trujillo and David Rabinowitz at the Palomar Observatory in California. The resonant trans-Neptunian object stays in a 2:5 resonance with Neptune. It has a reddish color, a rotation period of 56.1 hours and measures at least 500 kilometers (310 miles) in diameter.

## Orbit and classification

2002 TC$_{302}$ orbits the Sun at a distance of 39.2–71.4 AU once every 410 years and 12 months (150,105 days; semi-major axis of 55.28 AU). Its orbit has an eccentricity of 0.29 and an inclination of 35° with respect to the ecliptic. In December 2058, It will come to perihelion (minimum distance from the Sun) at 39.2 AU, which is about the same as Pluto's semi-major axis (average distance from the Sun). Given the long orbit that TNOs have around the Sun, 2002 TC$_{302}$ comes to opposition in late October of each year at an apparent magnitude of 20.5.
Both the Minor Planet Center (MPC) and the Deep Ecliptic Survey (DES) show 2002 TC$_{302}$ to be a resonant trans-Neptunian object in a 2:5 resonance with Neptune, meaning it completes two orbits for every five orbits of Neptune.

## Physical characteristics

2002 TC$_{302}$ has an absolute magnitude of 3.78. It has an estimated diameter of 584.1+105.6 −88.0 km. Using the Spitzer Space Telescope, it was previously estimated to have a diameter of 1145+337 −325 km, which would have made it one of the largest TNOs. This overestimation was due to insufficient motion to allow for a good sky subtraction, and because 2002 TC$_{302}$ was very close to a brighter background object. Brown noted that the Spitzer measurement involved a very large potential error and that the object would likely be much smaller.
The red spectra suggests that 2002 TC$_{302}$ has very little fresh ice on its surface. Its rotation period was initially estimated by Thirouin et al. to be 5.41 h, based on a light-curve amplitude of 0.04±0.01 mag. However, this short rotation period was most likely an alias due to a bias for shorter and more easily discernable shorter periods. 2002 TC$_{302}$ is highly oblate, and Ortiz et al. suggest a longer rotation period estimate of 56.1 hours.
An occultation of a 15.3 magnitude star by 2002 TC$_{302}$ on 28 January 2018 over Europe suggests that it has highly oblate shape with dimensions of 543.2±18 × 459.5±11 km and a projected axial ratio of a/c=1.18. The area equivalent diameter of 2002 TC$_{302}$ is 499.6 km.
On 11 November 2021, an occultation across North America and Europe detected an oblate shape of 530 × 467 km (mean 499 km), in strong agreement with the 2018 occultation results. No satellites were detected.

## Possible satellite

The mean diameter of 2002 TC$_{302}$ determined from occultations in 2018 is smaller than the larger diameter estimate of 584.1+105.6 −88.0 km by Spitzer in 2008. Despite the large uncertainty in the Spitzer's estimate, the difference of ~84 km between the two diameters is significant, implying that 2002 TC$_{302}$ may have a large satellite with a possible size range of 100–300 km, nearly as large as 2002 TC$_{302}$ itself. This possible satellite is expected to orbit 2002 TC$_{302}$ at a very close distance of less than 2000 km, close enough to slow down 2002 TC$_{302}$'s rotation through tidal interactions.
If both the primary body and satellite are doubly tidally locked, then the expected orbital period of the satellite would be approximately 54 hours, equal to 2002 TC$_{302}$'s rotation. Given an orbital period of 54 hours, the satellite's estimated orbital separation from the primary would be 1780 km, with an angular separation of 58 milliarcseconds, too small to be resolved with current space telescopes such as Hubble. Under the assumption the satellite's diameter is 200 km, it would cause 2002 TC$_{302}$'s position to oscillate by 18 milliarcseconds as it orbits around its barycenter.