1. The Stunning Four Galilean Moons! By, yours truly: James Hutchins Tidwell (Hutch) 4/7/11 Science 5 th period Mrs. Spaulding

2. IO Io has many volcanoes and pictures have shown lava erupting. Io is barely larger than Earth’s moon, it is the third largest of the four. One important element of the atmosphere is sulfur dioxide. It was discovered by Galileo Galilei in 1610 January 8 th. Io has the most active volcanoes in the solar system and has the tallest mountain in the solar system.

3. Europa Europa's surface is mostly water ice, and there is evidence that it may be covering an ocean of water or slushy ice beneath. Europa is thought to have twice as much water as does Earth. This moon is cool to scientists because of its possibility of having a "habitable zone." Life forms have been found thriving near volcanoes on Earth and in other extreme locations that may be analogues to what may exist on Europa.

4. Ganymede Ganymede is the largest and heaviest moon in the Solar System. It has a strong composition, with a molten core of iron or iron alloys, a mantle of silicate rocks, and a surface layer of water ice about 500 miles (800 km) in thickness. Ganymede has a trace atmosphere of oxygen but no observable weather patterns. Like Earth, and unlike Mars, Ganymede sustains both a magnetic field and plate tectonics. Its terrain is distinguished by shallow, eroded impact craters; dark plains formed by ancient lava flows; and an extensive pattern of grooves.

5. Callisto Callisto consists of a mixture of rock and ice in proportions not too different from those observed in Ganymede. However, measurements by the Galileo spacecraft establish that Callisto's interior is almost completely undifferentiatedCallisto has no metallic core, no magnetic field, and no plate tectonics. It is also the least reflective of the Galilean moons, suggesting that its icy terrain includes substantial dust. The surface of Callisto is saturated by cratering, meaning that every one of its craters either contains or intersects with another. Callisto is otherwise quite flat, without mountains, grooves, or ridges. Its topography has remained unchanged for billions of years, simply gathering dust. A trace atmosphere of carbon dioxide has been noted.