The Red Planet Mars was also a volcanically active world and there is evidence that geothermal activity is still present on this terrestrial world. Mars boasts the largest volcano in the solar system, named Mt. Olympus. This shield volcano is a whopping 374 miles (624 km) in diameter (the same size as the state of Arizona), 16 miles high (25 km), and is rimmed by a four-mile-high (6 km) escarpment. The volcanos main crater or caldera is 50-miles wide (80 km).
Beyond Mars, volcanoes are still plentiful but they are not found on the surfaces of the gas giant planets as far as we know. Instead, scientists have found evidence of unusual volcanoes on the moons of Jupiter, Saturn, Uranus and Neptune.
Io, the orange and red pizza-faced moon of Jupiter, is slightly larger than the Moon. It is a space teenager pimpled by dozens of active sulphur volcanoes. First discovered during the flyby of Voyager 1 in 1979, the erupting Ionian volcanoes send vast plumes of ejecta into space. Sulphur dust spreads across Ios orbit and lightly dusts a nearby smaller moon.
Some researchers have suggested that so-called ice volcanism may be active on Saturn's moons Enceladus and Titan. A moon of Uranus may also have ice volcanoes. On Neptunes moon Triton, ice volcanoes erupt on a regular basis. The ejecta of these bizarre volcanoes probably contain liquid nitrogen, methane and rocky debris.
Beyond Neptune, the outermost planet Pluto may also have volcanoes on its frozen surface, but well have to await NASAs robotic New Horizon spacecraft, set to arrive at Pluto around 2015, to find out for sure.
Whats in the Sky: The full Moon moves through the constellation Virgo April 1. Look for the bright star, Alpha Virginis (Spica), below the Moon. Located far away at a distance of 260 light years, this violent double star emits deadly X-rays that can be detected on Earth!
Lou Varricchio lives in Vermont. He was a former NASA science writer is the current NASA/JPL solar system ambassador for Vermont.