Regular moon

In astronomy, a regular moon is a natural satellite following a relatively close and prograde orbit with little orbital inclination or eccentricity. They are believed to have formed in orbit about their primary, as opposed to irregular moons, which were captured.

There are at least 55 regular satellites of the eight planets: one at Earth, eight at Jupiter, 22 named regular moons at Saturn (not counting hundreds or thousands of moonlets), 18 known at Uranus, and 6 small regular moons at Neptune. (Large Triton appears to have been captured.) It is thought that Pluto's five moons and Haumea's two were formed in orbit about those dwarf planets out of debris created in giant collisions.

See also

• Irregular moon
• Inner moon

Natural satellites of the Solar System
Planetary satellites	Terrestrial Martian Jovian Saturnian Uranian Neptunian
Other satellites	Asteroid moons Plutonian Haumean Eridian Makemakean
Largest satellites (mean radius ≥ 100 km)	size Ganymede largest / 2634 km / 0.413 Earths Titan Callisto Io Moon Europa Triton Titania Rhea Oberon Iapetus Charon Umbriel Ariel Dione Tethys [Dysnomia] Enceladus Miranda Proteus Mimas [Hi'iaka] Nereid Hyperion Phoebe smallest / 106 km / 0.017 Earths abc's Ariel Callisto Charon Dione [Dysnomia] Enceladus Europa Ganymede [Hi'iaka] Hyperion Iapetus Io Mimas Miranda Moon Nereid Oberon Phoebe Proteus Rhea Tethys Titan Titania Triton Umbriel
Discovery timeline Inner moons Irregular moons List Naming Regular moons Trojan moons NOTE: Italicized moons are not close to being in hydrostatic equilibrium; [bracketed] moons may or may not be close to being in hydrostatic equilibrium.