Ymir (moon)
Ymir, or Saturn XIX, is the second-largest retrograde irregular moon of Saturn.
Discovery and Naming
It was discovered by Brett J. Gladman, et al. in 2000, and given the temporary designation S/2000 S 1. Joint with Paaliaq, its discovery in 2000 was the first detection of an irregular moon of Saturn after the Phoebe discovery a century earlier.It was named in August 2003 after Ymir, who in Norse mythology is the ancestor of all the Jotuns or frost giants.
Orbit
The average distance from Ymir to Saturn is approximately 23 million kilometers. This makes it one of Saturn's largest known moons, and it takes 3.6 years to orbit the planet in a retrograde orbit. Its orbital inclination is 173° to the ecliptic, and its eccentricity is 0.337. Its orbit changes continuously due to solar and planetary perturbations.Due to its orbital inclination, Ymir belongs to the Phoebe subgroup, a retrograde group of moons that orbit Saturn at a distance of 13 million to 27 million kilometers, have orbital inclinations between 172.5 and 180, and have eccentricities of about 0.1 and 0.5.
Physical characteristics
Ymir's diameter is estimated at 19 km, assuming an albedo of 6%.Of the moons that take more than 3 Earth years to orbit Saturn, Ymir is the largest. Ymir is also the second largest member of the Norse group, after Phoebe.
Spectral measurements from Cassini–Huygens show that Ymir is reddish in color, unlike Phoebe's, which is colored grey.
Ymir rotating in a retrograde direction about once every 11.9 hours.
It shows a similar light curve as Siarnaq and has a therefore triangular shape, and it could be that Ymir is a contact binary system, as most of the measured light curves show very large brightness variations.
Origin
Ymirprobably did not form near Saturn but was captured by Saturn later.Like the other members of the Norse group, which have similar orbits, Ymir is probably the remnant of a broken, captured heliocentric asteroid.However, due to its color and different track characteristics, it is assumed that suggesting a separate origin for this moon.