Ymir (moon)

Ymir /ˈiːmɪər/, or Saturn XIX, is the second-largest retrograde irregular moon of Saturn. It was discovered by Brett J. Gladman, et al. in 2000, and given the temporary designation S/2000 S 1. It was named in August 2003 after Ymir, who in Norse mythology is the ancestor of all the Jotuns or frost giants.^[12]

Ymir

Discovery image of Ymir taken by the La Silla Observatory in August 2000
Discovery[1]
Discovered by	Brett J. Gladman
Discovery site	Observatoire de la Cote d'Azur
Discovery date	2000
Designations
Designation	Saturn XIX
Pronunciation	/ˈiːmɪər/,[2] /ˈɪmɪər/[3]
Named after	Ymir
Alternative names	S/2000 S 1
Adjectives	Ymirian /ɪˈmɪəriən/[a][5]
Orbital characteristics[6]
Epoch 2000 January 1.5
Semi-major axis	22957100 km
Eccentricity	0.337
Orbital period (sidereal)	−3.6 yr (−1315.16 d)
Mean anomaly	344.3°
Inclination	173.1°
Longitude of ascending node	61.5°
Argument of perihelion	90.8°
Satellite of	Saturn
Group	Norse group
Physical characteristics[7][8][9]
Dimensions	24 km × 22 km × 16 km
Mean diameter	19+50% −30% km
Circumference	65 km (equatorial)
Synodic rotation period	−11.92220±0.00002 h
North pole right ascension	280°±20°[b]
North pole declination	70°±10°[b]
Albedo	0.06[10]
Spectral type	D/P
Apparent magnitude	21.7[11]
Absolute magnitude (H)	12.3

It takes 3.6 Earth years to complete an orbit around Saturn. Of the moons that take more than 3 Earth years to orbit Saturn, Ymir is the largest, at about 19 kilometres (12 miles) in diameter;^[11] Ymir is also the second largest member of the Norse group, after Phoebe.^[9]

Spectral measurements from Cassini–Huygens show that Ymir is reddish in color, unlike Phoebe's gray color, suggesting a separate origin for this moon. It shows a similar light curve as Siarnaq and has a triangular shape, rotating in a retrograde direction about once every 11.9 hours.^[9]

Ymir imaged by the CFHT on 23 September 2000

3D model created based on lightcurve data

Notes

1. Because the -r is an inflectional ending, and the oblique stem is Ymi (as in Modern Norse Yme), one might expect the English adjective to be ?Ymian, but that is perhaps too short a word to be easily intelligible.^[4]
2. Assuming the north pole is the one pointing north of the invariable plane, in accordance with IAU standards.