Earth isnt the only world with volcanoes, active or extinct. Our nearest neighbor in space, the Moon, is covered with hundreds of volcanic features from cinder cones to vast lava fields.
While most of the lunar craters we see from Earth are the result of cosmic impacts, over 20 percent of the Moons physical features were actually formed by volcanic action. The great dark seas of the Moon, called maria in Latin, are vast plains of basaltic lava.
Planetary scientist Carlie Pieters of Brown University has discovered some volcanic features on the Moon that may be less than a million years old. Astronomers have even witnessed possible real-time volcanic events, such as the famous eruption in the lunar crater Alphonsus in November 1958. Astronomer Nikolay A. Kozyrev witnessed a pyroclastic volcanic eruption near the central peak of Alphonsus.
The planet Venus, blanketed in a thick atmosphere of carbon dioxide, nitrogen and sulphuric-acid gases, is riddled with thousands of volcanic featuresfrom large shield volcanoes to pimple-like pancake dome volcanoes similar to, but vastly larger than, Californias Mono Lake volcanic domes. Some scientists believe Venusian volcanism contributes to the planets soaring 800-degree F surface temperature.
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: Farewll to the summer of 2007. Autumn arrives here in the northern hemisphere Sept. 23. The event, called the equinox, happens when our Sun crosses the equator from north to south. The Sun rises due east and sets due west on the day of the equinox.