microsystem synonym

By 1978, nine distinct rings were identified. Uranus’s atmospheric drag appears to be so large that the present rings themselves may be short-lived. This is supported by the observations of a ring plane-crossing event in 2007, when the δ ring remained visible, which is consistent with the behavior of a simultaneously geometrically thick and optically thin ring. They deduced that a system of narrow rings was present. There is an inward gradually fading extension reaching to at least 32,600 km,[2] or possibly even to 27,000 km—to the atmosphere of Uranus. William Herschel originally proposed naming the planet "Georgium Sidus" ("George's Star") after King George III. The inner system of nine rings consists mostly of narrow, dark grey rings. The equivalent depth of the 1986U2R and ζ, The normal optical depths of all rings except ζ, ζ. Collisions between the tightly packed ring particles would naturally lead to an increase in the radial width of the rings. Resolution here is about 10 km (6 mi). The rings of Uranus were discovered in 1977, followed by that of Jupiter in 1979 and Neptune’s in 1989. [6] The former was named the η ring. [14], In addition to separate dust bands the system of Uranian rings appears to be immersed into wide and faint sheet of dust with the normal optical depth not exceeding 10−3. [12][23] The belts of the parent moonlets and particles are themselves invisible due to their low optical depth, while the dust reveals itself in forward-scattered light. 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. [21] During a ring plane-crossing event in 2007 the rings disappeared, which means they are geometrically thin like the ε ring and devoid of dust. [9] Two more faint rings were revealed, bringing the total to eleven. [21] The mean size of the ring particles is 0.2–20.0 m,[15] and the mean separation is around 4.5 times their radius. Later Earth-based observations revealed four additional rings. [15], The ε ring is known to have interior and exterior shepherd moons—Cordelia and Ophelia, respectively. [14] Observations in 2007 by the Keck telescope during the ring plane-crossing event confirmed this conclusion, because the λ ring became one of the brightest features in the Uranian ring system. The rings are extremely dark—the Bond albedo of the rings' particles does not exceed 2%. Later they found four additional rings: one between the β and γ rings and three inside the α ring. This ring was dubbed the ζ ring. [14] Like the ε ring, they exhibit regular variations in brightness and width. ", "The Occultation of SAO – 15 86687 by the Uranian Satellite Belt", "The Rings of Uranus: Results from 10 April 1978 Occultations", "Voyager 2 in the Uranian System: Imaging Science Results", "NASA's Hubble Discovers New Rings and Moons Around Uranus", "Dusty Rings and Circumplanetary Dust: Observations and Simple Physics", "Near-Infrared Absolute Photometric Imaging of the Uranian System", "New Dust Belts of Uranus: One Ring, Two Ring, Red Ring, Blue Ring", "Near-infrared adaptive optics imaging of the satellites and individual rings of Uranus", "Blue ring of Uranus linked to sparkling ice", Hubble Discovers Giant Rings and New Moons Encircling Uranus, Gazetteer of Planetary Nomenclature – Ring and Ring Gap Nomenclature (Uranus), USGS, https://en.wikipedia.org/w/index.php?title=Rings_of_Uranus&oldid=989536549, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License, This page was last edited on 19 November 2020, at 15:33. In this geometry the rings are much brighter, which indicates that they contain much micrometer-sized dust. [2] Rather different appearances of the 1986U2R and ζ rings may be caused by different viewing geometries: back-scattering geometry in 2003–2007 and side-scattering geometry in 1986. Combining the brightness of the rings observed in Voyager images with the equivalent widths from occultations shows that the ring particles reflect less than 5 percent of the incident sunlight. [12] In contrast, the Neptunian ring system is quite similar to that of Uranus, although it is less complex, darker and contains more dust; the Neptunian rings are also positioned further from the planet. [14] This means that their albedo is much lower when they are observed slightly off the opposition. [29], Rings 6, 5 and 4 are the innermost and dimmest of Uranus's narrow rings. [10], The peak brightness of the μ ring lies almost exactly on the orbit of the small Uranian moon Mab, which is probably the source of the ring’s particles. [8] The newly discovered outer ν and μ rings of Uranus are similar to the outer G and E rings of Saturn. Back-scattered light is the light scattered at an angle close to 180° relative to the solar light (. [23], The rings were thoroughly investigated by the Voyager 2 spacecraft in January 1986. [13] The μ ring is the outermost of the pair, and is twice the distance from the planet as the bright η ring. They formed from the remnants of colliding moons that existed around the planet. The equivalent depth[d] of the ε ring is around 47 km and is invariant around the orbit. [8] In addition, dust bands observed between the main rings of Uranus may be similar to the rings of Jupiter. [9] Many of these bands were detected again in 2003–2004 by the Keck Telescope and during the 2007 ring-plane crossing event in backscattered light, but their precise locations and relative brightnesses were different from during the Voyager observations. The dust particle size distribution is thought to obey a power law with the index p = 2.5 ± 0.5. [7] Uranus's ring system was the second to be discovered in the Solar System, after that of Saturn. Only a small amount of dust was found in the main rings. Many of Uranus's other rings can be discerned inward of the Epsilon ring. Their nearly flat reflectance spectrum means that the particles are basically gray in colour. It has been claimed that Herschel gave accurate descriptions of the ε ring's size relative to Uranus, its changes as Uranus travelled around the Sun, and its color. [8] The most widely cited model for such confinement, proposed initially by Goldreich and Tremaine,[33] is that a pair of nearby moons, outer and inner shepherds, interact gravitationally with a ring and act like sinks and donors, respectively, for excessive and insufficient angular momentum (or equivalently, energy). [20] Two new faint rings—λ and 1986U2R—were discovered bringing the total number then known to eleven. Most of the microscopic particles were instead distributed in the spaces between the main rings, which suggests that the rings are losing mass as a result of collisions. [10][12] In addition to these well-known rings, there may be numerous optically thin dust bands and faint rings between them. Moons more massive than the rings can halt this spreading in a process called shepherding. Uranus’ Rings. [14] Two rings—ε and η—were resolved in the images revealing a complicated fine structure. [20] It shows significant unexplained azimuthal variations in normal optical depth and width. [25] The δ ring consists of two components: a narrow optically dense component and a broad inward shoulder with low optical depth. [15] The mechanism of confinement of such a narrow ring is not known, but it has been noticed that the sharp inner edge of the γ ring is in a 6:5 resonance with Ophelia. [9] Such behavior indicates that the ring is not optically thin. The thickness estimates are from Lane et al., 1986. The mean apparent magnitude of Uranus is 5.68 with a standard deviation of 0.17, making it near the limit of naked eye visibility. The nature of this material is not clear, but it may be organic compounds considerably darkened by the charged particle irradiation from the Uranian magnetosphere. The moon exerts a net torque on the ring, and, as the moon and ring exchange angular momentum, energy is dissipated by collisions among the ring particles. Equivalent widths are the product (more precisely, the integral) of the radial distance and the fraction of starlight blocked. [9] The broad component is geometrically thicker than the narrow component. After more than a decade, two more rings were discovered by the Voyager 2 spacecraft. Unlike the rings of Saturn, which are very bright and composed of water ice, the rings of Uranus are relatively dark. [8] The mass of the ε ring is estimated to be about 1016 kg. The ring system contains little dust overall; it consists mostly of large bodies 20 cm to 20 m in diameter. It is the only planet whose name is derived directly from a figure of Greek mythology. [14] They are the most inclined rings, and their orbital eccentricities are the largest excluding the ε ring. [12] The normal optical depth of this dust is 10−4–10−3. The main rings have more centimeter to meter-sized bodies. Voyager 2 detected a 10th ring and found indications of others. To date, there are 13 rings to Uranus. The calculated orbital lifetimes are so short—1,000 years—that the dust must be rapidly and continually created. [10] These rings were subsequently named the μ and ν rings. [1] Herschel drew a small diagram of the ring and noted that it was "a little inclined to the red". [9] This moon clears a dark lane just inside the λ ring. [8], The rings were directly imaged when the Voyager 2 spacecraft flew through the Uranian system in 1986. [15] Some of them became visible during a series of ring plane-crossing events in 2007. In order of increasing distance from Uranus, they are: 1986U2R/ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν and μ. [16], Detailed analysis of the Voyager 2 images revealed azimuthal variations in the brightness of the λ ring. It wasn't firmly established for 70 years after its discovery. In 2003 and 2005, two more rings were observed by the Hubble Space Telescope. [21], The geometric thickness of the ε ring is not precisely known, although the ring is certainly very thin—by some estimates as thin as 150 m.[15] Despite such infinitesimal thickness, it consists of several layers of particles. [9] The masses of the α and β rings are estimated to be about 5 × 1015 kg (each)—half the mass of the ε ring. The dust has a very short lifetime, 100–1000 years, and should be continuously replenished by collisions between larger ring particles, moonlets and meteoroids from outside the Uranian system. They planned to use the occultation of the star SAO 158687 by Uranus to study the planet's atmosphere. [20] Like the δ ring, it consists of two components: a narrow optically dense component and a broad outward shoulder with low optical depth. The geometric albedo of the ring particles does not exceed 5–6%, while the Bond albedo is even lower—about 2%. Indeed, occultation observations conducted from the ground and the spacecraft showed that its normal optical depth[c] varies between 0.5 and 2.5,[21][22] being highest near the periapsis. [4] These designations have been used as the rings' names since then. During a ring plane-crossing event in 2007 the γ ring disappeared, which means it is geometrically thin like the ε ring[15] and devoid of dust. [9] Analysis of Voyager's images also led to discovery of eleven inner moons of Uranus, including the two shepherd moons of the ε ring—Cordelia and Ophelia.[9]. [20] The widths of these rings are 4.8–10 km and 6.1–11.4 km, respectively. [12] This observation, together with the wavelength dependence of the optical depth, indicates that the λ ring contains significant amount of micrometre-sized dust. Vary over the course of its orbit planet was encircled by five narrow rings.! Became visible during a stellar occultation at the wavelength 3.6 cm near 's. 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