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In the Solar System, many of the asteroid-sized moons have retrograde orbits, whereas all the large moons except Triton (the largest of Neptune's moons) have prograde orbits. [13] The particles in Saturn's Phoebe ring are thought to have a retrograde orbit because they originate from the irregular moon Phoebe.
The convention is that the normal orbit is prograde, an orbit in the same direction as the planet rotates. Inclinations greater than 90° describe retrograde orbits (backward). Thus: An inclination of 0° means the orbiting body has a prograde orbit in the planet's equatorial plane.
Two prograde moons of Saturn do not definitively belong to either the Inuit or Gallic groups. [1] S/2004 S 24 and S/2006 S 12 have similar orbital inclinations as the Gallic group, but have much more distant orbits with semi-major axes of ~400 Saturn radii and ~340 Saturn radii, respectively. [84] [13] [1]
The inclination and semi-major axis are represented on the Y and X-axis, respectively. The satellites with inclinations below 90° are prograde, those above 90° are retrograde. The X-axis is labeled in terms of Saturn's Hill radius. The Gallic group is a dynamical grouping of the prograde irregular satellites of Saturn following similar orbits.
The orbits of the known irregular satellites are extremely diverse, but there are certain patterns. Retrograde orbits are far more common (83%) than prograde orbits. No satellites are known with orbital inclinations higher than 60° (or smaller than 130° for retrograde satellites); moreover, apart from Nereid, no irregular moon has inclination ...
This added momentum means that the inner moon's distance from Saturn and orbital period are increased, and in exchange the outer moon's are decreased. The timing and magnitude of the momentum exchange is such that the moons effectively swap orbits, never approaching closer than about 10,000 km. At each encounter Janus's orbital radius changes ...
Orbits of Jupiter's Galilean moons, demonstrating the organized, low-eccentricity orbits typical of regular satellites. Regular moons are characterized by prograde orbits, usually with little orbital inclination or eccentricity relative to their parent body. These traits are largely constrained by their origins and subsequent tidal interactions ...
The region of stability for retrograde orbits at a large distance from the primary is larger than the region for prograde orbits at a large distance from the primary. This was thought to explain the preponderance of retrograde moons around Jupiter; however, Saturn has a more even mix of retrograde/prograde moons so the reasons are more ...