17 Thetis

17 Thetis 17 Thetis symbol.svg
Star field showing asteroid Thetis in the center
Discovery [1]
Discovered byR. Luther
Discovery siteDüsseldorf-Bilk Obs.
Discovery date17 April 1852
MPC designation(17) Thetis
Pronunciations/ (THEE-tis)
Named after
Thetis (Greek mythology)[2]
1954 SO1 · A913 CA
A916 YF
main-belt[3] · (inner)
Orbital characteristics[1]
Epoch 16 February 2017 (JD 2457800.5)
Uncertainty parameter 0
Observation arc164.55 yr (60,102 days)
Aphelion2.7987 AU
Perihelion2.1436 AU
2.4712 AU
3.88 yr (1,419 days)
18.87 km/s
0° 15m 13.32s / day
Physical characteristics
90±3.7km (IRAS)[5]
Mass1.2×1018 kg[7][a]
Mean density
3.21±0.92 g/cm³[7]
B–V = 0.829[1]
U–B = 0.438[1]
S (Tholen)[1]
Sl (SMASS)[1] · S[8]
7.76[1][5][6] · 7.85[9]

Thetis (THEE-tis; minor planet designation: 17 Thetis) and provisional designation A913 CA, is a stony asteroid from the inner regions of the asteroid belt, approximately 90 kilometers in diameter. It was discovered on 17 April 1852, by German astronomer Robert Luther at Bilk Observatory in Düsseldorf, Germany.[3] He named his first asteroid discovery after Thetis from Greek mythology.[2]


The asteroid orbits the Sun at a distance of 2.1–2.8 AU once every 3 years and 11 months (1,419 days). Its orbit has an eccentricity of 0.13 and an inclination of 6° with respect to the ecliptic.[1]

The spectrum of this object indicates that it is an S-type asteroid with both low and high calcium forms of pyroxene on the surface, along with less than 20% olivine. The high-calcium form of pyroxene forms 40% or more of the total pyroxene present, indicating a history of igneous rock deposits. This suggests that the asteroid underwent differentiation by melting, creating a surface of basalt rock.[10]

The mass of Thetis has been calculated from perturbations by 4 Vesta and 11 Parthenope. In 2007, Baer and Chesley calculated Thetis to have a mass of 1.2×1018 kg[a] with a density of 3.21 g/cm³.[7]

One Thetidian stellar occultation was observed from Oregon in 1999. However, the event was not timed.

This minor planet was named after Thetis, the mother of Achilles in Greek mythology.[2]

Other Languages
Alemannisch: (17) Thetis
asturianu: 17 Thetis
Bân-lâm-gú: 17 Thetis
беларуская: (17) Фетыда
български: 17 Тетида
bosanski: 17 Tetis
català: (17) Thetis
Deutsch: (17) Thetis
Ελληνικά: 17 Θέτις
español: (17) Thetis
Esperanto: 17 Tetiso
euskara: 17 Tetis
فارسی: ثتیس ۱۷
français: (17) Thétis
한국어: 17 테티스
հայերեն: (17) Թետիս
Bahasa Indonesia: 17 Thetis
italiano: 17 Thetis
коми: Фетида
Latina: 17 Thetis
latviešu: 17 Tetīda
Lëtzebuergesch: (17) Thetis
magyar: 17 Thetis
مازِرونی: سیارک ۱۷
norsk: 17 Thetis
norsk nynorsk: 17 Thetis
occitan: (17) Thetis
Plattdüütsch: (17) Thetis
polski: (17) Thetis
português: 17 Tétis
română: 17 Thetis
русский: (17) Фетида
Scots: 17 Thetis
slovenčina: 17 Thetis
slovenščina: 17 Tetija
српски / srpski: 17 Тетида
srpskohrvatski / српскохрватски: 17 Thetis
suomi: 17 Thetis
svenska: 17 Thetis
Tagalog: 17 Thetis
українська: 17 Фетіда
Tiếng Việt: 17 Thetis
Yorùbá: 17 Thetis
粵語: 海女星
中文: 海女星