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

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/
Named after	Τυφών Typhōn
Alternative designations	2002 CR46
Minor planet category	SDO; Centaur;
Adjectives	Typhonian /taɪˈfoʊniən/
Orbital characteristics
	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; 162±7 km
Mass	≈9.082×1017 kg
Mean density	0.66+0.09; −0.08 g/cm3
Synodic rotation period	9.67 h (0.403 d)
Geometric albedo	0.044±0.003; 0.10±0.02
Spectral type	B−V=0.74±0.02 V−R=0.52±0.01
Absolute magnitude (H)	7.5

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.

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]

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.

Moon

A large moon was identified in 2006. It is named Echidna (formal designation (42355) Typhon I Echidna), 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.

References

^ "Typhon". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ ^a ^b "JPL Small-Body Database Browser: (42355 Typhon)" (2008-03-14 last obs). Retrieved 12 April 2016.
^ "List Of Centaurs and Scattered-Disk Objects". Minor Planet Center. Retrieved 2008-09-21.
^ (42355) Typhon and Echidna
^ "Typhonian". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ ^a ^b ^c ^d Duffard, R.; Pinilla-Alonso, N.; Santos-Sanz, P.; Vilenius, E.; Ortiz, J. L.; Mueller, T.; et al. (April 2014). ""TNOs are Cool": A survey of the trans-Neptunian region. XI. A Herschel-PACS view of 16 Centaurs". Astronomy and Astrophysics. 564: 17. arXiv:1309.0946. Bibcode:2014A&A...564A..92D. doi:10.1051/0004-6361/201322377. S2CID 119177446.
^ ^a ^b Santos-Sanz, P., Lellouch, E., Fornasier, S., Kiss, C., Pal, A., Müller, T. G., Vilenius, E., Stansberry, J., Mommert, M., Delsanti, A., Mueller, M., Peixinho, N., Henry, F., Ortiz, J. L., Thirouin, A., Protopapa, S., Duffard, R., Szalai, N., Lim, T., Ejeta, C., Hartogh, P., Harris, A. W., & Rengel, M. (2012). “TNOs are Cool”: A Survey of the Transneptunian Region IV - Size/albedo characterization of 15 scattered disk and detached objects observed with Herschel Space Observatory-PACS
^ K. Noll; H. Levison; W. Grundy; D. Stephens (October 2006). "Discovery of a binary Centaur". Icarus. 184 (2): 611. arXiv:astro-ph/0605606. Bibcode:2006Icar..184..611N. doi:10.1016/j.icarus.2006.05.010. S2CID 18927838.
^ J. L. Elliot; S. D. Kern; K. B. Clancy; A. A. S. Gulbis; R. L. Millis; M. W. Buie; et al. (February 2005). "The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population" (PDF). The Astronomical Journal. 129 (2): 1117. Bibcode:2005AJ....129.1117E. doi:10.1086/427395.
^ "Echidna". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ François Hartog (Janet Lloyd, trans., 1988) The Mirror of Herodotus, p. 25
^ J. A. Weinstock (2014) The Ashgate Encyclopedia of Literary and Cinematic Monsters, p. 79
^ George Sandys (1669) Ovid's Metamorphosis Englished, 6th ed., p. 134.

External links

42355 Typhon at the JPL Small-Body Database
- Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters

This article about a centaur (minor planet) or trans-Neptunian object is a stub. You can help Wikipedia by expanding it.

[1] "Typhon". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)

[jpldata-2] "JPL Small-Body Database Browser: (42355 Typhon)" (2008-03-14 last obs). Retrieved 12 April 2016.

[MPC-3] "List Of Centaurs and Scattered-Disk Objects". Minor Planet Center. Retrieved 2008-09-21.

[johnstons-archive-4] (42355) Typhon and Echidna

[5] "Typhonian". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)

[TNOsCool11-6] Duffard, R.; Pinilla-Alonso, N.; Santos-Sanz, P.; Vilenius, E.; Ortiz, J. L.; Mueller, T.; et al. (April 2014). ""TNOs are Cool": A survey of the trans-Neptunian region. XI. A Herschel-PACS view of 16 Centaurs". Astronomy and Astrophysics. 564: 17. arXiv:1309.0946. Bibcode:2014A&A...564A..92D. doi:10.1051/0004-6361/201322377. S2CID 119177446.

[TNOsCool4-7] Santos-Sanz, P., Lellouch, E., Fornasier, S., Kiss, C., Pal, A., Müller, T. G., Vilenius, E., Stansberry, J., Mommert, M., Delsanti, A., Mueller, M., Peixinho, N., Henry, F., Ortiz, J. L., Thirouin, A., Protopapa, S., Duffard, R., Szalai, N., Lim, T., Ejeta, C., Hartogh, P., Harris, A. W., & Rengel, M. (2012). “TNOs are Cool”: A Survey of the Transneptunian Region IV - Size/albedo characterization of 15 scattered disk and detached objects observed with Herschel Space Observatory-PACS

[Noll2006-BinaryCentar-8] K. Noll; H. Levison; W. Grundy; D. Stephens (October 2006). "Discovery of a binary Centaur". Icarus. 184 (2): 611. arXiv:astro-ph/0605606. Bibcode:2006Icar..184..611N. doi:10.1016/j.icarus.2006.05.010. S2CID 18927838.

[DES_Elliot2005-9] J. L. Elliot; S. D. Kern; K. B. Clancy; A. A. S. Gulbis; R. L. Millis; M. W. Buie; et al. (February 2005). "The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population" (PDF). The Astronomical Journal. 129 (2): 1117. Bibcode:2005AJ....129.1117E. doi:10.1086/427395.

[10] "Echidna". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)

[Moon-adj-11] François Hartog (Janet Lloyd, trans., 1988) The Mirror of Herodotus, p. 25

[Moon-adj-2-12] J. A. Weinstock (2014) The Ashgate Encyclopedia of Literary and Cinematic Monsters, p. 79

[Moon-adj-3-13] George Sandys (1669) Ovid's Metamorphosis Englished, 6th ed., p. 134.

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