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.