42355 Typhon (; provisional designation 2002 CR46) is a scattered disc object that was discovered on February 5, 2002, by the NEAT program. It measures 162±7 km in diameter, and is named after Typhon, a monster in Greek mythology. Typhon is the first known binary centaur, using an extended definition of a centaur as an object on a non-resonant (unstable) orbit with the perihelion inside the orbit of Neptune.
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Symbol
Planetary symbols are no longer much used in astronomy, so Typhon never received a symbol in the astronomical literature. There is no standard symbol for Typhon used by astrologers either. A hurricane symbol () has been used, which might be identified with U+1F300 🌀︎ CYCLONE (U+FE0E ︎ VARIATION SELECTOR-15 is used to make the character display as text).
Physical properties
Measurements of its thermal radiation led to an equivalent diameter of about either 138±9 km or 185±7 km, with the latter value preferable. The diameter of the central body (Typhon) is in the latter case 162±7 km. Due to its small size, it is unlikely to be classified as a dwarf planet. As of 2021, no rotational lightcurve has been analyzed and the body's actual shape remain unknown.
Typhon has a BR taxonomic class, with a blue surface. It has a resulting B–R color difference of about 1.3, while V–I color difference is about unity. The spectra of Typhon show the presence of water ice and possibly of water altered silicates.
Satellite
A large moon was identified in 2006. It is named Echidna (formal designation (42355) Typhon I), after the monstrous mate of Typhon. It orbits Typhon at the distance of 1628±29 km, completing one orbit in 18.9709±0.0064 days. Its diameter is estimated at 89±6 km. Echidna has the same color as Typhon.