Io’s volcanic plumes are visible to the Hubble Space Telescope.
The Jovian moon Io is Jupiter’s third largest and the fifth closest to the planet. Io is a differentiated planetary body, with a molten iron core, rocky mantle and silicate crust. Io was named after a mythological Greek nymph, one of Zeus’ concubines. If it orbited the sun, Io would be called a dwarf planet, like Pluto. Io was discovered by Galileo in 1610.
The giant gas planet Jupiter is the largest in the solar system. Its gravitational field holds 60 known small satellites and four large ones in orbit. Called Jovian moons, the orbiting bodies were the first moons discovered around a planet besides the Earth. The four largest rocky bodies are know as Galilean moons after their discoverer, Galileo Galilei. Io is the most colorful and geologically active of the Jovian moons.
The Jovian moon Io is one of the solar system’s most visually interesting objects. Its rocky, mountainous surface is multicolored with hues of orange, red, white, green, brown and black from lava flows and plumes. Io’s overall yellow color comes from sulfur and sulfurous compounds ejected by volcanoes. The most conspicuous features on Io are its tall mountains, some with peaks over 50,000 feet, and its massive 190-mile high volcanic plumes. Compared to other bodies in the Solar System, Io has very few meteorite craters.
With around 400 volcanoes, Io is the most volcanically active body in the solar system. Its volcanic vents and shield volcanoes produce rings of lava hundreds of miles across. Io’s erupting volcanoes were first recorded by the spacecraft Voyager 1 and 2 in 1979. Io’s volcanoes are the hot spots of the solar system, with temperatures reaching 2,789 degrees Fahrenheit, nearly one third as hot as the sun’s surface. Oddly, Io’s surface temperature away from the volcanoes is only 238 degrees below zero Fahrenheit.
The gravitational fields of Jupiter and the other Galilean Jovian moons, Europa and Ganymede, pull Io into an elliptical orbit. The irregular orbit causes massive tides in the moon’s internal magma ocean. The tidal forces move the moon’s surface up and down 330 feet. The resulting friction causes high heat and pressure in the crust’s molten subsurface. The melted ultramafic rocks, sulfur and related compounds form volcanoes to relieve the internal pressure. Liquid lava fills in impact craters and smooths the moon’s surface with molten floodplains.