It has no water to speak of, unlike the other, colder Galilean moons. Sulfur dioxide is the primary constituent of a thin atmosphere on Io. 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). 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 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. Credit: NASA Visualization Technology Applications and Development (VTAD)
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.Ī 3D model of Io, a volcanic moon of Jupiter. Io can develop 400,000 volts across itself and create an electric current of 3 million amperes. Io's orbit, keeping it at more or less a cozy 262,000 miles (422,000 kilometers) from Jupiter, cuts across the planet's powerful magnetic lines of force, thus turning Io into a electric generator. 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. Compare these tides on Io's solid surface to the tides on Earth's oceans. These forces cause Io's surface to bulge up and down (or in and out) by as much as 330 feet (100 meters). Thus, in its widely varying distances from Jupiter, Io is subjected to tremendous tidal forces. Orbit and RotationĪlthough 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. Size and DistanceĪ bit larger than Earth's Moon, Io is the third largest of Jupiter's moons, and the fifth one in distance from the planet. Io’s remarkable activity is the result of a tug-of-war between Jupiter's powerful gravity and smaller but precisely timed pulls from two neighboring moons that orbit farther from Jupiter – Europa and Ganymede. Spahr, G.Jupiter's rocky moon Io is the most volcanically active world in the solar system, with hundreds of volcanoes, some erupting lava fountains dozens of miles (or kilometers) high. NameĪs many as 17 more satellites of Jupiter have been found and scientists continue to search for more.
The small outermost moons may be asteroids captured by the gravitational pull of Jupiter. The other, smaller moons have their orbits either between Jupiter and Io, or outside the orbit of Callisto. The four largest - Io, Europa, Ganymede and Callisto - were discovered by Galileo in 1610 and are known as the Galilean Satellites. Jupiter has numerous moons, which make the Jovian system much like a miniature solar system.
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