Jupiter Moon Io

Io can be classified as one of the most unusual moons in our solar system. Discovery of active volcanism on Io was the greatest unexpected discovery at Jupiter. It was the first time active volcanoes had been seen on another body in the solar system. Together, the Voyagers observed the eruption of nine volcanoes on Io. There is also evidence that other eruptions occurred between Voyager encounters. Plumes from the volcanos extend to more than 300 kilometers (190 miles) above the surface with material being ejected at speeds up to a kilometer per second.

Io's volcanoes are apparently due to heating of the satellite by tidal pumping. Io is perturbed in its orbit by Europa and Ganymede, two other large satellites nearby, then pulled back again into its regular orbit by Jupiter. This tug-of-war results in tidal bulging as great as 100 meters (330 feet) on Io's surface.

Io is composed mostly of rocky material with very little iron. Io is located within an intense radiation belt of electrons and ions trapped in Jupiter's magnetic field. As the magnetosphere rotates with Jupiter, it sweeps past Io and strips away about 1,000 kilograms (1 ton) of material per second. The material forms a torus, a doughnut-shaped cloud of ions that glow in the ultraviolet. The torus's heavy ions migrate outward, and their pressure inflates the jovian magnetosphere to more than twice its expected size. Some of the more energetic sulfur and oxygen ions fall along the magnetic field into the planet's atmosphere, resulting in auroras.

Io acts as an electrical generator as it moves through Jupiter's magnetic field, developing 400,000 volts across its diameter and generating an electric current of 3 million amperes that flows along the magnetic field to the planet's ionosphere.

Views of Io

Title Image: Voyager 1 took this picture of Io on March 4, 1979. The brown, orange, areas are probably covered by sulphur of a mixture containing sulphur. The light ares may be sulphur dioxide snow and the pock-marks are mostly volcanic calderas up to 200 km across. Mountainous regions exist near both poles, with some features rising 8 km or more above their surroundings.

Volcanic Plumes: Voyager 2 took this picture of Io on the evening of July 9, 1979, from a range of 1.2 million kilometers. On the limb of Io are two blue volcanic eruption plumes about 100 kilometers high. These two plumes were first seen by voyager 1 in March 1979 and are designated Plume 5 (upper) and Plume 6 (lower). They have apparently been erupting for a period of at least four months and probably longer. A total of six plumes have been seen by voyager 2, all of which were first seen by Voyager 1. The largest plume viewed by Voyager 1, Plume 1, is no longer erupting. Plume 4 was not viewed on the edge of Io's disc by Voyager 2 and therefore it is not known whether or not it is still erupting. (Courtesy NASA/JPL).

Io Surface: This is a close up view of the surface of Io in the northern hemisphere. The central feature has been named Loki Patera.

Io Statistics

Radius:                 1816 km
Mass:                   8.92 x 10^25 kg
Density:                3.55 gm/cm^3
Distance from Jupiter:  412,600 km
Orbital period:         1.769 days
Rotational period:      1.769 days

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