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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.
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.
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]
Neptune also has eight more outer irregular satellites other than Triton, including Nereid, whose orbits are much farther from Neptune and at high inclination: three of these have prograde orbits, while the remainder have retrograde orbits. In particular, Nereid has an unusually close and eccentric orbit for an irregular satellite, suggesting ...
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.
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 ...
Proteus is the second-largest moon of Neptune and is the largest of its regular prograde moons. It is about 420 km (260 mi) in diameter, larger than Nereid, Neptune's third-largest moon. It was not discovered by Earth-based telescopes because Proteus orbits so close to Neptune that it is lost in the glare of reflected sunlight. [15]
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 ...