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Why do many of Saturnās outer moons have retrograde orbits?
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Saturn
Saturn and its spectacular rings, in a natural-color composite of 126 images taken by the Cassini spacecraft on October 6, 2004. The view is directed toward Saturn's southern hemisphere, which is tipped toward the Sun. Shadows cast by the rings are visible against the bluish northern hemisphere, while the planet's shadow is projected on the rings to the left.
Many of Saturnās outer moons have retrograde orbits because they are not considered primordial moons that formed alongside the planet. Instead, these outer bodies appear to be objects that were captured by Saturnās gravity or are fragments resulting from such captures.1
These outer moons, which orbit beyond approximately 11 million km (6.8 million miles) from the planet, are classified as irregular. Unlike the inner, regular moonsāwhich formed in the equatorial plane from a protoplanetary diskāthese irregular moons are characterized by orbits with large eccentricities and high inclinations, with about two-thirds revolving in a retrograde direction, meaning they move opposite to the planetās rotation.1