Chapter 8: Moons, Rings, and Pluto

Goals Describe the Galilean Moons Describe Saturn’s largest Moon Titan Describe the nature and detailed structure of Saturn’s rings Describe why astronomers no longer consider Pluto a planet

Chapter 8: Moons, Rings, and Pluto Images of Jupiter’s moons with Jupiter in the background. Io has volcanoes and Europa may have oceans.

Chapter 8: Moons, Rings, and Pluto All four of the Jovian planets have moons, rings that display fascinating variety and complexity. Before spacecraft, most astronomers would have identified the planets as the most interesting, but now we know the moons of the planets appear much more interesting. Many of the moons display terrestrial planet like features. Most scientists believe that Jupiter’s moon Europa and Saturn’s moon Titan are the best candidates for finding other life in the Solar system.

Chapter 8: Moons, Rings, and Pluto

Depending on your definition of what a moon is Jupiter has 16, Saturn has 18, Uranus has 15, Neptune has 8 Since many of the moons reflect a lot of light they must be covered with highly reflective material or ice. While Saturn is best known for its rings, all the Jovian planets have ring systems. Pluto is considered as a separate case since it does not fall neatly into either terrestrial or Jovian categories.

Chapter 8: Moons, Rings, and Pluto Jupiter’s most interesting moons are its largest and were first seen by Galileo and are called the Galilean satellites in his honor.

Chapter 8: Moons, Rings, and Pluto Io reminds me of a fresh Pizza. Its surface must be young since we don’t see any craters caused by impact. We do see volcanic craters though and have even photographed several volcanoes in action. Given its small size, Io should be geologically dead. It is kept alive by the tidal heating due to Jupiter’s tides. The orange color is due to compounds of sulfur. The other moons prevent Io from being synchronous which would have prevented the tides from heating up the moon.

Chapter 8: Moons, Rings, and Pluto Europa is quite different from Io, although it too has a young surface as evidenced by few craters. Its surface displays a vast network of criss-crossed lines. We think Europa has vast oceans of liquid water which is frozen on the surface and became cracked by Jupiter’s tidal forces. Because of the tidal forces inside Europa, many think the underground oceans are still liquid. This we think may be a good place to look for life.

Chapter 8: Moons, Rings, and Pluto Ganymede is the largest moon in the solar system. It appears to be moonlike in many aspects and has several craters and “ripples” from the largest impacts that looks like water may have played a role in its past.

Chapter 8: Moons, Rings, and Pluto Callisto Callisto although similar to Ganymede, has fewer craters and fault lines. Its largest feature is concentric rings around two large basins which resembles “ripples” made when a stone hits the water. Callisto is a frozen, dead moon with a surface older than Ganymede’s.