Like Europa, Callisto's icy surface may conceal an ocean. It also saw deep canyons and broad, smooth plains created by the motions of Ganymede's crust.
IO MOON MOUNTAINS PLUS
Grooves and ridges that crisscross its surface indicate that it has undergone great changes over the eons.ĭuring several passes, the Galileo spacecraft saw mountains of ice, plus sheets of ice that erupted from volcanoes. It consists of about half ice and half rock and metal. Ganymede is the solar system's largest moon - larger than the planet Mercury. In addition, the motions of salty water below the surface may generate Europa's weak magnetic field. The ridges may form as Jupiter's gravity rips apart the thin ice sheet. The other terrain consists of smooth plains marked by ridges that are hundreds of miles long. "Chaotic" terrain looks like icebergs breaking off glaciers on Earth. The Galileo spacecraft found two types of terrain that may be related to water. Tidal gravity may have created the ocean by heating Europa enough to melt some of its ice. Europa's icy crust appears to cover a large ocean of liquid water, where life may have gained a foothold. As observations continued to show a sterile, desolate world, though, scientists began turning their attention to Europa. Europa: Water World?įor decades, Mars was considered the most likely home for life in the solar system. That heats Io's interior enough to melt some of its rock, which "bubbles" to the surface. But as the other moons move past Io, their gravity tugs at it, too. Io is "locked" so that the same hemisphere always faces the planet, just as the same hemisphere of our own moon always faces Earth. Io's interior is heated by a tug-of-war between Jupiter and the planet's other big moons. Several hundred volcanoes dot the surface, and they belch sulfur-rich lava that is hundreds of degrees hotter than the hottest lava on Earth. Other than the Sun, portions of Io offer the hottest surface in the solar system. It is an eerie landscape of active volcanoes, tall mountains, and plains covered with frozen sulfur. For a true hot-spot, they might show us the surface of Io, one of the moons of Jupiter. Robotic probes may someday provide close-up views of some of the most remarkable vistas in the solar system, from the canyons of Mars to the ice-geysers of Triton.
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