SPACE

This is a montage of New Horizons images of Jupiter and its volcanic moon Io, taken during the spacecraft’s Jupiter flyby . The image was released in Oct. 2007. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute) Jupiter's fifth moon, Io, is the most volcanically active body in the solar system. Plumes of sulfur spew upward as high as 190 miles (300 kilometers). The surface of Io is splotched with lava lakes and floodplains of liquid rock. Astronomers have mapped about 150 volcanoes on the moon, some of which blast lava 250 miles (400 km) out into space. There are volcanoes all over Io's surface, and as scientists perform observations they still occasionally see new hotspots pop up. For example, NASA's Juno spacecraft, which is currently orbiting Jupiter, found a possible new hotspot on Io on Dec. 16, 2017. Io by the numbers Age: Io is about 4.5 billion years old, about the same age as Jupiter. Distan...

Ganymede is the largest moon in the solar system, and is larger than the planet Mercury. If it were not orbiting as Jupiter’s largest moon, it could be considered a dwarf planet. Ganymede is the only moon in the solar system known to have a substantial magnetosphere. That implies there is something inside helping to generate a strong magnetic field. Like Europa, Ganymede is thought to have a subsurface ocean, overlying a liquid iron and nickel core. That core is what helps generate the magnetic field. The surface of Ganymede is icy and covered with two main types of landscape: young, lighter regions and darker, older and cratered terrain. The dark areas appear to contain clays and organic materials. Ganymede was likely formed in place around the infant Jupiter in the early solar system. Several smaller worlds likely accreted together to make this moon. Ganymede has a thin atmosphere that a...