Janus

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Janus
Janus is an inner satellite of Saturn. It is also known as Saturn X. It is named after the mythological Janus. Janus's orbit is co-orbital with that of Epimetheus. Janus's mean orbital radius from Saturn is, as of 2006 , only 50 km less than that of Epimetheus, a distance smaller than either moon's mean radius. In accordance with Kepler's laws of planetary motion, the closer orbit is completed more quickly. Because of the small difference it is completed in only about 30 seconds less. Each day, the inner moon is an additional 0.25° farther around Saturn than the outer moon. As the inner moon catches up to the outer moon, their mutual gravitational attraction increases the inner moon's momentum and decreases that of the outer moon. This added momentum means that the inner moon's distance from Saturn and orbital period are increased, and the outer moon's are decreased. Janus (moon) - Wikipedia, the free encyclopedia
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Short Description Janus is an inner satellite of Saturn. It is also known as Saturn X. It is named after the mythological Janus. Janus's orbit is co-orbital with that of Epimetheus. Janus's mean orbital radius from Saturn is, as of 2006 , only 50 km less than that of Epimetheus, a distance smaller than either moon's mean radius. In accordance with Kepler's laws of planetary motion, the closer orbit is completed more quickly. Because of the small difference it is completed in only about 30 seconds less. Each day, the inner moon is an additional 0.25° farther around Saturn than the outer moon. As the inner moon catches up to the outer moon, their mutual gravitational attraction increases the inner moon's momentum and decreases that of the outer moon. This added momentum means that the inner moon's distance from Saturn and orbital period are increased, and the outer moon's are decreased. Janus (moon) - Wikipedia, the free encyclopedia
Discovered by Audouin Charles Dollfus
Discovery date 15 December 1966
Type Moon
AddInfo Saturn X
Satellite of Saturn
Orbit Prograde
Rotation Synchronous
Apoapsis 06 152 490 km
Periapsis 06 150 430 km
Semi-major axis 06 151 460 km
Distance from Sun 01 9.554 909 au /07b
Eccentricity 0.006 8
Orbital period 0.694 660 342 day
Orbital speed  15.8 km/s
Inclination to the equator 000.163°
Diameter/Size 03 178.8 ± 6.0 km
Dimensions 203 × 185 × 152.6 km
Mass 1018×1.897 5 kg
Density  0.63 ± 0.03 g/cm3
Surface gravity  0.011 – 0.017 m/s2
Escape velocity 02 55 m/s
Rotation period 0.694 660 342 day
Axial tilt 000.015°
Albedo geometric 0.71 ± 0.02
Apparent magnitude 14.0
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