Known Space -- Sol -- Jupiter -- | Io |
Io is the fifth of Jupiter's known satellites and the third largest; it is the innermost of the Galilean moons. Io is slightly larger than Earth's Moon.
In contrast to most of the moons in the outer solar system, Io and Europa may be somewhat similar in bulk composition to the terrestrial planets, primarily composed of molten silicate rock. Io has an iron core (mixed with iron sulfide) with a radius of 900 km.
Io's surface is radically different from any other body in the solar system. It has a very young surface covered with hundreds of volcanic calderas. Some of the volcanoes are active! The material erupting from Io's vents is a mix of sulfur and sulfur dioxide.
Io has an amazing variety of terrains: calderas up to several kilometers deep, lakes of molten sulfur, mountains which are apparently NOT volcanoes, extensive flows hundreds of kilometers long of a low viscosity molten silicate rock, and volcanic vents. Sulfur and its compounds take on a wide range of colors which are responsible for Io's varigated appearance.
Some of the hottest spots on Io may reach temperatures of 700 K (even 900 K has been reported), though the average is much lower, about 130 K. These hot spots are the principal mechanism by which Io loses its heat.
The energy for all this activity is derived from tidal interactions between Io, Europa, Ganymede and Jupiter. These three moons are locked into resonant orbits such that Io orbits twice for each orbit of Europa which in turn orbits twice for each orbit of Ganymede. Though Io, like Earth's Moon always faces the same side toward its planet, the effects of Europa and Ganymede cause it to wobble a bit. This wobbling stretches and bends Io by as much as 100 meters (a 100 meter tide!) and generates heat the same way a coat hanger heats up when bent back and forth. (Lacking another body to perturb it, the Moon is not heated by Earth in this way.)
Io also cuts across Jupiter's magnetic field lines, generating an electric current. Though small compared to the tidal heating, this current may carry more than 1 trillion watts. It also strips some material away from Io which forms a torus of intense radiation around Jupiter. Particles escaping from this torus are partially responsible for Jupiter's unusually large magnetosphere.
Orbital Distance: 421,600 km (average) Eccentricity: 0.004 Local Year: 1.769 days (1d 18h 27m 33.5s) Orbital Velocity: 17.332 km/s Inclination: 0.040° Local Day: 1.769 days (1d 18h 27m 33.5s) Axial Tilt: n/a Diameter: 3,630 km Composition: Basaltic rock with sulphides Density: 3.53 g/cm3 Mass: 8.94 x 1019 tonnes (0.015 earths) Gravity: 0.183 G Escape Velocity: 2.558 km/s Area: 41.7 million km2 Surface Material: Sulfur compounds Atmosphere: SO2, S, and Na Pressure: Very thin Albedo: 0.61 Temperature: -143°C |