Jupiter's moon Io is the most volcanically active body in the Solar System. The huge tidal forces exerted by the gas giant and its other moons power an estimated 300 sulphur-spewing volcanoes that constantly resurface Io.
Photo: A volcanic plume over Io (top right) taken by the New Horizons probe (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
Jupiter's moon is the Solar System's most volcanically active body.
The probe discovers the most volcanically active body in the Solar System.
NASA scientists were surprised to find that Io is the Solar System's most volcanically active body. The Voyager probes, launched in 1977, showed them Io's numerous volcanoes. The constant sulphur eruptions across Io's surface are powered by Jupiter's strong gravitational attraction, which heats the interior of the moon.
Prof Brian Cox explores the speed of light.
Prof Brian Cox demonstrates how Danish astronomer Ole Romer discovered that light has a fixed speed.
Jupiter's moons aren't the cold, dead worlds the experts expected.
Voyager scientists thought Jupiter's moons would be cold, dead worlds. They were amazed when the first close-up images from the spacecraft revealed four moons, each different from the next. The probes were launched in 1977.
Jupiter's moon Io is stretched and squashed.
Professor Brian Cox explains the incredible volcanism on Jupiter's moon Io.
Sir Patrick Moore is amazed by the detail of Voyager 1's images.
Early in Voyager 1's mission, Sir Patrick Moore and his guest Dr Garry Hunt of University College London discussed some of the probe's findings, which included a ring around Jupiter and images of Jupiter's moons Amalthea, Callisto, Io, Europa and Ganymede. Since Sir Patrick and Dr Hunt spoke, Jupiter has been found to have three faint rings.
Io (/ˈaɪ.oʊ/) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of 3,642 kilometres (2,263 mi), the fourth-largest moon in the Solar System. It was named after the mythological character Io, a priestess of Hera who became one of the lovers of Zeus.
With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io's interior as it is pulled between Jupiter and the other Galilean satellites—Europa, Ganymede and Callisto. Several volcanoes produce plumes of sulfur and sulfur dioxide that climb as high as 500 km (300 mi) above the surface. Io's surface is also dotted with more than 100 mountains that have been uplifted by extensive compression at the base of Io's silicate crust. Some of these peaks are taller than Mount Everest. Unlike most satellites in the outer Solar System, which are mostly composed of water ice, Io is primarily composed of silicate rock surrounding a molten iron or iron sulfide core. Most of Io's surface is composed of extensive plains coated with sulfur and sulfur dioxide frost.
Io's volcanism is responsible for many of its unique features. Its volcanic plumes and lava flows produce large surface changes and paint the surface in various shades of yellow, red, white, black, and green, largely due to allotropes and compounds of sulfur. Numerous extensive lava flows, several more than 500 km (300 mi) in length, also mark the surface. The materials produced by this volcanism make up Io's thin, patchy atmosphere and Jupiter's extensive magnetosphere. Io's volcanic ejecta also produce a large plasma torus around Jupiter.
Io played a significant role in the development of astronomy in the 17th and 18th centuries. It was discovered in 1610 by Galileo Galilei, along with the other Galilean satellites. This discovery furthered the adoption of the Copernican model of the Solar System, the development of Kepler's laws of motion, and the first measurement of the speed of light. From Earth, Io remained just a point of light until the late 19th and early 20th centuries, when it became possible to resolve its large-scale surface features, such as the dark red polar and bright equatorial regions. In 1979, the two Voyager spacecraft revealed Io to be a geologically active world, with numerous volcanic features, large mountains, and a young surface with no obvious impact craters. The Galileo spacecraft performed several close flybys in the 1990s and early 2000s, obtaining data about Io's interior structure and surface composition. These spacecraft also revealed the relationship between Io and Jupiter's magnetosphere and the existence of a belt of radiation centered on Io's orbit. Io receives about 3,600 rem (36 Sv) of radiation per day.
Further observations have been made by Cassini–Huygens in 2000 and New Horizons in 2007, as well as from Earth-based telescopes and the Hubble Space Telescope as technology has advanced.
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