The yellow ring in the image to the left was deposited by the volcanic plume Prometheus which has been an active site of volcanism for over 20 years. Over this time, the source of plume has shifted 70 km to the west. Most scientists believe that the source for this long-lived plume is from a vent lying at the west end of the dark lava flow in the image. However, there is some speculation that the plume might be a product of the advancing lava as it flows over and volatilizes the SO 2 -rich surface.
An example of a spectacular ring of red pyroclastic debris comes from the active volcanic plume Pele , shown in the two Galileo images below. These images were taken less than six months apart. Note the dramatic change that has occurred over this time period near the volcano Pillan Petera , marked by the red arrow.
The April image shows the simple caldera of Pillan Petra located within the red pyroclastic ring of the Pele plume. However, the September image shows a circular, dark deposit about km in diameter surrounding the caldera. The dark deposit covers an area about as large as the state of Arizona and is most likely composed of silicate-rich pyroclastic material. A spectacular example of active lava production is demonstrated in the second pair of images shown below. These images, taken three months apart, lie within a chain of giant calderas known as Tvashtar Catena.
The November image on the left displays a fissure eruption arrow that appears to be generating a " curtain of fire " which is a typical feature displayed by many Hawaiian-type eruptions on Earth.
The fissure shown here is about 40 km long and the "curtain of fire" extruding from it appears to rise about 1. The eruption appears to be associated with the generation of active lava flows at the base of the fissure. The second image, to the right, was taken three months later in the February That was enough reason for some commentators to call Jupiter and its moons a mini solar system.
Initially, only four moons were discovered, but that was in the s. Io, the moon named after a nymph, was among the first four discovered. To know Io, one must first know how it was discovered. In , Galileo discovered four big moons around Jupiter. Hence, the moons were called Galilean satellites. He named them by numbers, one to four. At the same time, Simon Marius was also studying Jupiter and discovered the four moons. Marius was an independent scientist and discovered the moons on his own, but he went through a dispute with Galileo as to who discovered the moons first.
In the end, it was revealed that Marius started taking notes about the moons only one day later than Galileo. The orbital resonances around Io are important to understand why Io works as it does. The two innermost moons of Jupiter are Io and Europa. A bit larger than Earth's Moon, Io is the third largest of Jupiter's moons, and the fifth one in distance from the planet.
Although Io always points the same side toward Jupiter in its orbit around the giant planet, the large moons Europa and Ganymede perturb Io's orbit into an irregularly elliptical one.
Thus, in its widely varying distances from Jupiter, Io is subjected to tremendous tidal forces. These forces cause Io's surface to bulge up and down or in and out by as much as feet meters. Compare these tides on Io's solid surface to the tides on Earth's oceans. On Earth, in the place where tides are highest, the difference between low and high tides is only 60 feet 18 meters , and this is for water, not solid ground.
Io's orbit, keeping it at more or less a cozy , miles , kilometers from Jupiter, cuts across the planet's powerful magnetic lines of force, thus turning Io into a electric generator.
Io can develop , volts across itself and create an electric current of 3 million amperes. This current takes the path of least resistance along Jupiter's magnetic field lines to the planet's surface, creating lightning in Jupiter's upper atmosphere. The tidal forces generate a tremendous amount of heat within Io, keeping much of its subsurface crust in liquid form seeking any available escape route to the surface to relieve the pressure.
Thus, the surface of Io is constantly renewing itself, filling in any impact craters with molten lava lakes and spreading smooth new floodplains of liquid rock. The composition of this material is not yet entirely clear, but theories suggest that it is largely molten sulfur and its compounds which would account for the varied coloring or silicate rock which would better account for the apparent temperatures, which may be too hot to be sulfur.
Galileo first referred to this moon as Jupiter I. In the mids, the moon was renamed Io. Zeus the counterpart for the Roman god Jupiter fell in love with her, but turned her into a cow to avoid being caught with her by his wife, Hera or Juno. Several spacecraft have flown by Jupiter and its moons. Pioneer 10 arrived first, in , followed by Pioneer 11 in Voyager 1 and Voyager 2 returned striking photos during their flybys.
The Galileo spacecraft passed as low as miles km over the surfaces of the Galilean moons and produced detailed images. The interior of Io is composed of an iron or iron sulfide core and a brown silicate outer layer, giving the planet a splotchy orange, yellow, black, red, and white appearance. Based on data from scientific computer models, Io formed in a region around Jupiter where water ice was plentiful. Io's heat, combined with the possibility that there was water on Io shortly after it was formed, could have made life possible, although Jupiter's radiation would have removed the water from the surface.
The moon's most distinctive features are its volcanoes. Aside from Earth, Io is the only known body in the solar system to have observed active volcanoes.
While Galileo had made some cryptic notes inferring possible volcanic activity, NASA's Voyager spacecraft discovered Io's volcanoes in The volcanic activity is a result of Io being stretched and squeezed as it orbits Jupiter. Io's rock surface bulges up and down by as much as meters feet during the process.
This affects Io's volcanic activity in a similar way to which Earth's oceans react to the moon.
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