Co-orbital configurationIn astronomy, a co-orbital configuration is a configuration of two or more astronomical objects (such as asteroids, moons, or planets) orbiting at the same, or very similar, distance from their primary, i.e. they are in a 1:1 mean-motion resonance. (or 1:−1 if orbiting in opposite directions). There are several classes of co-orbital objects, depending on their point of libration. The most common and best-known class is the trojan, which librates around one of the two stable Lagrangian points (Trojan points), and , 60° ahead of and behind the larger body respectively.
Kerberos (moon)Kerberos is a small natural satellite of Pluto, about in its longest dimension. Kerberos is also the second-smallest moon of Pluto, after Styx. It was the fourth moon of Pluto to be discovered and its existence was announced on 20 July 2011. It was imaged, along with Pluto and its four other moons, by the New Horizons spacecraft in July 2015. The first image of Kerberos from the flyby was released to the public on 22 October 2015.
Styx (moon)Styx is a small natural satellite of Pluto whose discovery was announced on 11 July 2012. It was discovered by use of the Hubble Space Telescope, and is the smallest of the five known moons of Pluto. It was imaged along with Pluto and Pluto's other moons by the New Horizons spacecraft in July 2015, albeit poorly with only a single image of Styx obtained. Styx is the second-closest known satellite to Pluto, and the fifth discovered. It was discovered one year after Kerberos.
Nix (moon)Nix is a natural satellite of Pluto, with a diameter of across its longest dimension. It was discovered along with Pluto's outermost moon Hydra on 15 May 2005 by astronomers using the Hubble Space Telescope, and was named after Nyx, the Greek goddess of the night. Nix is the third moon of Pluto by distance, orbiting between the moons Styx and Kerberos. Nix was imaged along with Pluto and its other moons by the New Horizons spacecraft as it flew by the Pluto system in July 2015.
Hydra (moon)Hydra is a natural satellite of Pluto, with a diameter of approximately across its longest dimension. It is the second-largest moon of Pluto, being slightly larger than Nix. Hydra was discovered along with Nix by astronomers using the Hubble Space Telescope on 15 May 2005, and was named after the Hydra, the nine-headed underworld serpent in Greek mythology. By distance, Hydra is the fifth and outermost moon of Pluto, orbiting beyond Pluto's fourth moon Kerberos.
Inner moonIn astronomy, an inner moon or inner natural satellite is a natural satellite following a prograde, low-inclination orbit inwards of the large satellites of the parent planet. They are generally thought to have been formed in situ at the same time as the coalescence of the original planet. Neptune's moons are an exception, as they are likely reaggregates of the pieces of the original bodies, which were disrupted after the capture of the large moon Triton.
Quasi-satelliteA quasi-satellite is an object in a specific type of co-orbital configuration (1:1 orbital resonance) with a planet (or dwarf planet) where the object stays close to that planet over many orbital periods. A quasi-satellite's orbit around the Sun takes the same time as the planet's, but has a different eccentricity (usually greater), as shown in the diagram. When viewed from the perspective of the planet by an observer facing the Sun, the quasi-satellite will appear to travel in an oblong retrograde loop around the planet.
Pandora (moon)Pandora is an inner satellite of Saturn. It was discovered in 1980 from photos taken by the Voyager 1 probe, and was provisionally designated S/1980 S 26. In late 1985 it was officially named after Pandora from Greek mythology. It is also designated Saturn XVII. Pandora was thought to be an outer shepherd satellite of the F Ring. However, recent studies indicate that it does not play such a role, and that only Prometheus, the inner shepherd, contributes to the confinement of the narrow ring.
Kozai mechanismIn celestial mechanics, the Kozai mechanism is a dynamical phenomenon affecting the orbit of a binary system perturbed by a distant third body under certain conditions. It is also known as the von Zeipel-Kozai-Lidov, Lidov–Kozai mechanism, Kozai–Lidov mechanism, or some combination of Kozai, Lidov–Kozai, Kozai–Lidov or von Zeipel-Kozai-Lidov effect, oscillations, cycles, or resonance. This effect causes the orbit's argument of pericenter to oscillate about a constant value, which in turn leads to a periodic exchange between its eccentricity and inclination.
Atlas (moon)Atlas is an inner satellite of Saturn which was discovered by Richard Terrile in 1980 from Voyager photos and was designated S/1980 S 28. In 1983 it was officially named after Atlas of Greek mythology, because it "holds the rings on its shoulders" like the Titan Atlas held the sky up above the Earth. It is also designated Saturn XV. Atlas is the closest satellite to the sharp outer edge of the A ring, and was long thought to be a shepherd satellite for this ring.
