Io has a density of 3. Galileo 's magnetometer failed to detect an internal, intrinsic magnetic field at Io, suggesting that the core is not convecting. Unlike Earth and the Moon, Io's main source of internal heat comes from tidal dissipation rather than radioactive isotope decay, the result of Io's orbital resonance with Europa and Ganymede. The resonant orbit also helps to maintain Io's distance from Jupiter; otherwise tides raised on Jupiter would cause Io to slowly spiral outward from its parent planet.
The friction or tidal dissipation produced in Io's interior due to this varying tidal pull, which, without the resonant orbit, would have gone into circularizing Io's orbit instead, creates significant tidal heating within Io's interior, melting a significant amount of Io's mantle and core. The amount of energy produced is up to times greater than that produced solely from radioactive decay. Although there is general agreement that the origin of the heat as manifested in Io's many volcanoes is tidal heating from the pull of gravity from Jupiter and its moon Europa , the volcanoes are not in the positions predicted with tidal heating.
They are shifted 30 to 60 degrees to the east. The movement of this magma would generate extra heat through friction due to its viscosity. The study's authors believe that this subsurface ocean is a mixture of molten and solid rock. Other moons in the Solar System are also tidally heated, and they too may generate additional heat through the friction of subsurface magma or water oceans.
This ability to generate heat in a subsurface ocean increases the chance of life on bodies like Europa and Enceladus. Based on their experience with the ancient surfaces of the Moon, Mars, and Mercury, scientists expected to see numerous impact craters in Voyager 1 's first images of Io.
The density of impact craters across Io's surface would have given clues to Io's age. However, they were surprised to discover that the surface was almost completely lacking in impact craters, but was instead covered in smooth plains dotted with tall mountains, pits of various shapes and sizes, and volcanic lava flows.
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This result was spectacularly confirmed as at least nine active volcanoes were observed by Voyager 1. Io's colorful appearance is the result of materials deposited by its extensive volcanism, including silicates such as orthopyroxene , sulfur , and sulfur dioxide. Sulfur is also seen in many places across Io, forming yellow to yellow-green regions. Sulfur deposited in the mid-latitude and polar regions is often damaged by radiation, breaking up the normally stable cyclic 8-chain sulfur.
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This radiation damage produces Io's red-brown polar regions. Explosive volcanism , often taking the form of umbrella-shaped plumes, paints the surface with sulfurous and silicate materials. Plume deposits on Io are often colored red or white depending on the amount of sulfur and sulfur dioxide in the plume. These red deposits consist primarily of sulfur generally 3- and 4-chain molecular sulfur , sulfur dioxide, and perhaps sulfuryl chloride. Compositional mapping and Io's high density suggest that Io contains little to no water , though small pockets of water ice or hydrated minerals have been tentatively identified, most notably on the northwest flank of the mountain Gish Bar Mons.
The tidal heating produced by Io's forced orbital eccentricity has made it the most volcanically active world in the Solar System, with hundreds of volcanic centres and extensive lava flows. Io's surface is dotted with volcanic depressions known as paterae which generally have flat floors bounded by steep walls. One hypothesis suggests that these features are produced through the exhumation of volcanic sills , and the overlying material is either blasted out or integrated into the sill.
Lava flows represent another major volcanic terrain on Io. Magma erupts onto the surface from vents on the floor of paterae or on the plains from fissures, producing inflated, compound lava flows similar to those seen at Kilauea in Hawaii. Images from the Galileo spacecraft revealed that many of Io's major lava flows, like those at Prometheus and Amirani , are produced by the build-up of small breakouts of lava flows on top of older flows.
Analysis of the Voyager images led scientists to believe that these flows were composed mostly of various compounds of molten sulfur.
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However, subsequent Earth-based infrared studies and measurements from the Galileo spacecraft indicate that these flows are composed of basaltic lava with mafic to ultramafic compositions. The discovery of plumes at the volcanoes Pele and Loki were the first sign that Io is geologically active. Additional material that might be found in these volcanic plumes include sodium, potassium , and chlorine.
Examples of this plume type include Pele, Tvashtar, and Dazhbog. Another type of plume is produced when encroaching lava flows vaporize underlying sulfur dioxide frost, sending the sulfur skyward. This type of plume often forms bright circular deposits consisting of sulfur dioxide.
Examples include Prometheus, Amirani, and Masubi. The erupted sulfurous compounds are concentrated in the upper crust from a decrease in sulfur solubility at greater depths in Io's lithosphere and can be a determinant for the eruption style of a hot spot.
Io has to mountains. Despite the extensive volcanism that gives Io its distinctive appearance, nearly all its mountains are tectonic structures, and are not produced by volcanoes. Instead, most Ionian mountains form as the result of compressive stresses on the base of the lithosphere, which uplift and often tilt chunks of Io's crust through thrust faulting. Mountains on Io generally, structures rising above the surrounding plains have a variety of morphologies.
Plateaus are most common. Other mountains appear to be tilted crustal blocks, with a shallow slope from the formerly flat surface and a steep slope consisting of formerly sub-surface materials uplifted by compressive stresses. Both types of mountains often have steep scarps along one or more margins. Only a handful of mountains on Io appear to have a volcanic origin. Other shield volcanoes with much shallower slopes are inferred from the morphology of several of Io's volcanoes, where thin flows radiate out from a central patera, such as at Ra Patera.
Nearly all mountains appear to be in some stage of degradation. Large landslide deposits are common at the base of Ionian mountains, suggesting that mass wasting is the primary form of degradation. Scalloped margins are common among Io's mesas and plateaus, the result of sulfur dioxide sapping from Io's crust, producing zones of weakness along mountain margins.
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Io has an extremely thin atmosphere consisting mainly of sulfur dioxide SO 2 , with minor constituents including sulfur monoxide SO , sodium chloride NaCl , and atomic sulfur and oxygen. The maximum atmospheric pressure on Io ranges from 3. The thin atmosphere also necessitates a rugged lander capable of enduring the strong Jovian radiation , which a thicker atmosphere would attenuate.
Gas in Io's atmosphere is stripped by Jupiter's magnetosphere, escaping to either the neutral cloud that surrounds Io, or the Io plasma torus, a ring of ionized particles that shares Io's orbit but co-rotates with the magnetosphere of Jupiter. The collapse during eclipse is limited somewhat by the formation of a diffusion layer of sulfur monoxide in the lowest portion of the atmosphere, but the atmosphere pressure of Io's nightside atmosphere is two to four orders of magnitude less than at its peak just past noon. Various researchers have proposed that the atmosphere of Io freezes onto the surface when it passes into the shadow of Jupiter.
Evidence for this is a "post-eclipse brightening", where the moon sometimes appears a bit brighter as if covered with frost immediately after eclipse. After about 15 minutes the brightness returns to normal, presumably because the frost has disappeared through sublimation. High-resolution images of Io acquired when Io is experiencing an eclipse reveal an aurora -like glow. Aurorae usually occur near the magnetic poles of planets, but Io's are brightest near its equator. Io lacks an intrinsic magnetic field of its own; therefore, electrons traveling along Jupiter's magnetic field near Io directly impact Io's atmosphere.
More electrons collide with its atmosphere, producing the brightest aurora, where the field lines are tangent to Io i. Aurorae associated with these tangent points on Io are observed to rock with the changing orientation of Jupiter's tilted magnetic dipole. Media related to Io at Wikimedia Commons.
From Wikipedia, the free encyclopedia. For other uses, see Jupiter 1. Innermost of the four Galilean moons of Jupiter. Galileo spacecraft true-color image of Io. The dark spot just left of the center is the erupting volcano Prometheus. The whitish plains on either side of it are coated with volcanically deposited sulfur dioxide frost, whereas the yellower regions contain a higher proportion of sulfur. Alternative names. Mean orbit radius. Orbital period. Average orbital speed. Surface area. Mean density. Surface gravity. Moment of inertia factor.
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Rotation period. Apparent magnitude. Surface pressure. Main article: Exploration of Io. Io's Laplace resonance with Europa and Ganymede click for animation. See also: Tidal heating. Main article: Tidal heating of Io. Play media. Main article: Volcanology of Io.