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.
Titania (moon)Titania (təˈtɑːniə,_təˈteɪniə), also designated Uranus III, is the largest of the moons of Uranus and the eighth largest moon in the Solar System at a diameter of , with a surface area comparable to that of Australia. Discovered by William Herschel in 1787, it is named after the queen of the fairies in Shakespeare's A Midsummer Night's Dream. Its orbit lies inside Uranus's magnetosphere. Titania consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky core and an icy mantle.
Oberon (moon)Oberon ˈoʊbərɒn, also designated Uranus IV, is the outermost major moon of the planet Uranus. It is the second-largest, with a surface area that is compareable to the area of Australia, and second most massive of the Uranian moons, and the ninth most massive moon in the Solar System. Discovered by William Herschel in 1787, Oberon is named after the mythical king of the fairies who appears as a character in Shakespeare's A Midsummer Night's Dream. Its orbit lies partially outside Uranus's magnetosphere.
Giant-impact hypothesisThe giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact, suggests that the Moon was formed from the ejecta of a collision between the early Earth and a Mars-sized planet, approximately 4.5 billion years ago in the Hadean eon (about 20 to 100 million years after the Solar System coalesced). The colliding body is sometimes called Theia, named after the mythical Greek Titan who was the mother of Selene, the goddess of the Moon.
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.
Ariel (moon)Ariel is the fourth-largest of the 27 known moons of Uranus. Ariel orbits and rotates in the equatorial plane of Uranus, which is almost perpendicular to the orbit of Uranus and so has an extreme seasonal cycle. It was discovered in October 1851 by William Lassell and named for a character in two different pieces of literature. As of 2019, much of the detailed knowledge of Ariel derives from a single flyby of Uranus performed by the space probe Voyager 2 in 1986, which managed to image around 35% of the moon's surface.
Synodic dayA synodic day (or synodic rotation period or solar day) is the period for a celestial object to rotate once in relation to the star it is orbiting, and is the basis of solar time. The synodic day is distinguished from the sidereal day, which is one complete rotation in relation to distant stars, which is the basis of sidereal time. This is different from the duration of a synodic day because the revolution of the body around its parent star would cause a single "day" to pass relative to a star, even if the body itself did not rotate.
Irregular moonIn astronomy, an irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit. They have been captured by their parent planet, unlike regular satellites, which formed in orbit around them. Irregular moons have a stable orbit, unlike temporary satellites which often have similarly irregular orbits but will eventually depart. The term does not refer to shape; Triton for example, is a round moon, but is considered irregular due to its orbit.
Planetary oceanographyPlanetary oceanography also called astro-oceanography or exo-oceanography is the study of oceans on planets and moons other than Earth. Unlike other planetary sciences like astrobiology, astrochemistry and planetary geology, it only began after the discovery of underground oceans in Saturn's moon Titan and Jupiter's moon Europa. This field remains speculative until further missions reach the oceans beneath the rock or ice layer of the moons.
