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Shepherd Satellite
A shepherd moon is a small natural satellite that clears a gap in planetary ring material or keeps particles within a ring contained. The name is a result of their limiting the "herd" of the ring particles as a shepherd. Due to their gravitational influence, shepherd moons deflect ring particles from their original orbits due to proximity or through orbital resonances. This can carve gaps in the ring system, such as the Encke Gap maintained by Saturn's moon Pan, or lead to the confining of narrow ringlets, such as Saturn's F ring. Discovery The existence of shepherd moons was theorized in early 1979. Observations of the rings of Uranus show that they are very thin and well defined, with sharp gaps between rings. To explain this, Goldreich and Tremaine suggested that two small satellites that were undetected at the time might be confining each ring. The first images of shepherd satellites were taken later that year by Voyager 1. Examples Jupiter Several of Jupiter's smal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Saturn
Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 times more massive. Even though Saturn is almost as big as Jupiter, Saturn has less than a third its mass. Saturn orbits the Sun at a distance of , with an orbital period of 29.45 years. Saturn's interior is thought to be composed of a rocky core, surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and an outer layer of gas. Saturn has a pale yellow hue, due to ammonia crystals in its upper atmosphere. An electrical current in the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than Earth's, but has a magnetic moment 580 times that of Earth because of Saturn's greater size. Saturn's magnetic field strength is about a twen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Galatea (moon)
Galatea , also known as Neptune VI, is the fourth-closest inner moon of Neptune, and fifth-largest moon of Neptune. It is named after Galatea, one of the fifty Nereids of Greek legend, with whom Cyclops Polyphemus was vainly in love. Discovery Galatea was discovered in late July 1989 from the images taken by the ''Voyager 2'' probe. It was given the temporary designation S/1989 N 4. The discovery was announced (IAUC 4824) on 2 August 1989, and mentions "10 frames taken over 5 days", implying a discovery date of sometime before July 28. The name was given on 16 September 1991. Physical properties Galatea is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit. Compositionally, Galatea appears to be similar to other small i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Voyager 2
''Voyager 2'' is a space probe launched by NASA on August 20, 1977, as a part of the Voyager program. It was launched on a trajectory towards the gas giants (Jupiter and Saturn) and enabled further encounters with the ice giants (Uranus and Neptune). The only spacecraft to have visited either of the ice giant planets, it was the List of artificial objects leaving the Solar System, third of five spacecraft to achieve Solar escape velocity, which allowed it to leave the Solar System#Farthest regions, Solar System. Launched 16 days before its twin ''Voyager 1'', the primary mission of the spacecraft was to study the outer planets and its extended mission is to study interstellar space beyond the Sun's heliosphere. ''Voyager 2'' successfully fulfilled its primary mission of visiting the Exploration of Jupiter, Jovian system in 1979, the Exploration of Saturn, Saturnian system in 1981, Exploration of Uranus, Uranian system in 1986, and the Exploration of Neptune, Neptunian system ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rings Of Neptune
The rings of Neptune consist primarily of five principal Planetary ring, rings. They were first discovered (as "arcs") by simultaneous observations of a stellar occultation on 22 July 1984 by André Brahic's and William B. Hubbard's teams at La Silla Observatory (ESO) and at Cerro Tololo Interamerican Observatory in Chile. They were eventually imaged in 1989 by the ''Voyager 2'' spacecraft. At their densest, they are comparable to the less dense portions of Rings of Saturn, Saturn's main rings such as the C ring and the Cassini Division, but much of Neptune's ring system is quite faint and Cosmic dust, dusty, in some aspects more closely resembling the rings of Jupiter. Neptune's rings are named after astronomers who contributed important work on the planet: Johann Gottfried Galle, Galle, Urbain Le Verrier, Le Verrier, William Lassell, Lassell, François Arago, Arago, and John Couch Adams, Adams. Neptune also has a faint unnamed ring coincident with the orbit of the moon Galatea (m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neptune
Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth. Compared to Uranus, its neighbouring ice giant, Neptune is slightly smaller, but more massive and denser. Being composed primarily of gases and liquids, it has no well-defined solid surface. Neptune orbits the Sun once every 164.8 julian year (astronomy), years at an orbital distance of . It is named after Neptune (mythology), the Roman god of the sea and has the astronomical symbol representing Trident of Poseidon, Neptune's trident. Neptune is not visible to the unaided eye and is the only planet in the Solar System that was not initially observed by direct empirical observation. Rather, unexpected changes in the orbit of Uranus led Alexis Bouvard to hypothesise that its orbit was subject to gravitational Pe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tidal Deceleration
Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite (e.g. the Moon) and the primary planet that it orbits (e.g. Earth). The acceleration causes a gradual recession of a satellite in a prograde orbit (satellite moving to a higher orbit, away from the primary body, with a lower orbital velocity and hence a longer orbital period), and a corresponding slowdown of the primary's rotation. See supersynchronous orbit. The process eventually leads to ''tidal locking'', usually of the smaller body first, and later the larger body (e.g. theoretically with Earth-Moon system in 50 billion years). The Earth–Moon system is the best-studied case. The similar process of tidal deceleration occurs for satellites that have an orbital period that is shorter than the primary's rotational period, or that orbit in a retrograde direction. These satellites will have a higher and higher orbital velocity and a shorter and shorter orbital period, until a final coll ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ophelia (moon)
Ophelia is a moon of Uranus. It was discovered from the images taken by ''Voyager 2'' on January 20, 1986, and was given the temporary designation S/1986 U 8. It was not seen again until the Hubble Space Telescope recovered it in 2003. Ophelia was named after the daughter of Polonius, Ophelia, in William Shakespeare's play ''Hamlet''. It is also designated Uranus VII. Other than its orbit, size of 54 × 38 km, and geometric albedo of 0.065, virtually nothing is known about it. In ''Voyager 2'', images Ophelia appears as an elongated object, with its major axis pointing towards Uranus. The ratio of axes of the Ophelia's prolate spheroid is 0.7 ± 0.3. Ophelia acts as the outer shepherd satellite for Uranus's ε ring. The orbit of Ophelia is within the synchronous orbit radius of Uranus, and is therefore slowly decaying due to tidal forces. See also * Moons of Uranus Uranus, the seventh planet of the Solar System, has 28 confirmed moons. The 27 with names a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cordelia (moon)
Cordelia is the innermost known moon of Uranus. It was discovered from the images taken by ''Voyager 2'' on January 20, 1986, and was given the temporary designation S/1986 U 7. It was not detected again until the Hubble Space Telescope observed it in 1997. Cordelia takes its name from the youngest daughter of Lear in William Shakespeare's ''King Lear.'' It is also designated Uranus VI. Other than its orbit, size of 50 × 36 km, and geometric albedo of 0.06, virtually nothing is known about it. In the ''Voyager 2'' images, Cordelia appears as an elongated object with its major axis pointing towards Uranus. The ratio of axes of Cordelia's prolate spheroid is . Cordelia acts as the inner shepherd satellite for Uranus's ε ring. Cordelia's orbit is within Uranus's synchronous orbit radius, and is therefore slowly decaying due to tidal deceleration. Cordelia is very close to a 5:3 orbital resonance In celestial mechanics, orbital resonance occurs when orbiti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epsilon Ring
The rings of Uranus consists of 13 planetary rings. They are intermediate in complexity between the more extensive set around Rings of Saturn, Saturn and the simpler systems around Rings of Jupiter, Jupiter and Rings of Neptune, Neptune. The planetary rings, rings of Uranus were discovered on March 10, 1977, by James L. Elliot, Edward W. Dunham, and Jessica Mink. William Herschel had also reported observing rings in 1789; modern astronomers are divided on whether he could have seen them, as they are very dark and faint.(re study by Stuart Eves) By 1977, nine distinct rings were identified. Two additional rings were discovered in 1986 in images taken by the ''Voyager 2'' spacecraft, and two outer rings were found in 2003–2005 in Hubble Space Telescope photos. In the order of increasing distance from the planet the 13 known rings are designated 1986U2R/ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν and μ. Their radii range from about 38,000 km for the 1986U2R/ζ ring to about ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranus
Uranus is the seventh planet from the Sun. It is a gaseous cyan-coloured ice giant. Most of the planet is made of water, ammonia, and methane in a Supercritical fluid, supercritical phase of matter, which astronomy calls "ice" or Volatile (astrogeology), volatiles. Atmosphere of Uranus, The planet's atmosphere has a complex layered cloud structure and has the lowest minimum temperature () of all the Solar System's planets. It has a marked axial tilt of 82.23° with a Retrograde and prograde motion, retrograde rotation period of 17 hours and 14 minutes. This means that in an 84-Earth-year orbital period around the Sun, its poles get around 42 years of continuous sunlight, followed by 42 years of continuous darkness. Uranus has the third-largest diameter and fourth-largest mass among the Solar System's planets. Based on current models, inside its volatile Mantle (geology), mantle layer is a rocky core, and surrounding it is a thick hydrogen and helium atmosphere. Trace amount ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epimetheus (moon)
Epimetheus is an inner satellite of Saturn. It is also known as Saturn XI. It is named after the mythological Epimetheus, brother of Prometheus. Discovery Epimetheus occupies essentially the same orbit as the moon Janus. Astronomers originally assumed that there was only one body in that orbit, disbelieving that two moons could share nearly identical orbits without eventually colliding. Thus, there was difficulty in determining their orbital characteristics. Observations were photographic and spaced widely apart in time, so that while the presence of two objects was obvious, the observations were difficult to reconcile with a reasonable orbit. Audouin Dollfus observed a moon on 15 December 1966, which he proposed to be named "Janus". On 18 December, Richard Walker made a similar observation which is now credited as the discovery of Epimetheus. However, at the time, it was believed that there was only one moon, unofficially known as "Janus", in the given orbit. Twel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
