42355 Typhon

42355 Typhon (/ˈtaɪfɒn/; 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.

42355 Typhon

Hubble Space Telescope image of Typhon and its moon Echidna, taken in 2006
Discovery
Discovered by	NEAT
Discovery date	5 February 2002
Designations
MPC designation	(42355) Typhon
Pronunciation	/ˈtaɪfɒn/[1]
Named after	Τυφών Typhōn
Alternative designations	2002 CR46
Minor planet category	SDO[2][3] Centaur[4]
Adjectives	Typhonian /taɪˈfoʊniən/[5]
Symbol	(rare)
Orbital characteristics[2]
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 2
Observation arc	9563 days (26.18 yr)
Aphelion	58.982252 AU (8.8236193 Tm)
Perihelion	17.545721 AU (2.6248025 Tm)
Semi-major axis	38.263987 AU (5.7242110 Tm)
Eccentricity	0.5414560
Orbital period (sidereal)	236.70 yr (86453.7 d)
Mean anomaly	14.61898075°
Mean motion	0° 0m 14.991s / day
Inclination	2.4252078°
Longitude of ascending node	351.9098598°
Argument of perihelion	159.3215723°
Known satellites	1 (Echidna)
TJupiter	4.692
Physical characteristics
Mean diameter	138±9 km[6] 162±7 km[7]
Mass	≈9.082×1017 kg[6]
Mean density	0.66+0.09 −0.08 g/cm3[6]
Synodic rotation period	9.67 h (0.403 d)[6]
Geometric albedo	0.044±0.003[7] 0.10±0.02
Spectral type	B−V=0.74±0.02 V−R=0.52±0.01
Absolute magnitude (H)	7.5

Typhon is the first known binary centaur,^[8] using an extended definition of a centaur as an object on a non-resonant (unstable) orbit with the perihelion inside the orbit of Neptune.^[9]

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).^[10]

Physical properties

Typhon has a BR taxonomic class, with a blue surface. It has a resulting B–R magnitude of 1.274.

Based on a conventional magnitude-to-diameter conversion, the body measures 162 km in diameter, with an albedo of 0.044 and a magnitude of 7.5. Mike Brown gives it a diameter of 192 km with a magnitude of 7.5. Due to its small size, it is unlikely to be classified as a dwarf planet. As of 2021, no rotational lightcurve has been analyzed. The body's rotational period, pole, and actual shape remain unknown.

Satellite

Echidna

Discovery
Discovery date	2006
Designations
MPC designation	(42355) Typhon I
Pronunciation	/ɪˈkɪdnə/[11]
Named after	Έχιδνα
Adjectives	Echidnian[12] Echidnean (rarely)[13] (both /ɪˈkɪdniən/)[14]
Orbital characteristics
Semi-major axis	~1300 km
Orbital period (sidereal)	11 d
Satellite of	Typhon
Physical characteristics
Dimensions	89±6 km

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 ~1300 km, completing one orbit in about 11 days. Its diameter is estimated to be 89±6 km.