1. Moons Jupiter is known to have at least 64 moons at the time this textbook was written. Most of them have synchronous orbits.

2. There are four Galilean moons which are about the size of Earth’s moon
There are four Galilean moons which are about the size of Earth’s moon. From closest to the planet to farthest they are: Io, Europa, Ganymede, and Callisto.

3. Within the orbit of Io there are four smaller moons.

4. Beyond Callisto there are eight smaller moons
Beyond Callisto there are eight smaller moons. The inner four of these eight have eccentric, inclined orbits. The outer four are fairly eccentric and retrograde.

5. The four small inner moons

6. Amalthea, the third moon

7. Thebe, the fourth moon

8. Each group probably represents a single body that was broken apart into the smaller moons that are present today.

9. Io - the densest, most geologically active object in the solar system.

13. Voyager 1 found eight erupting volcanoes
Voyager 1 found eight erupting volcanoes. Voyager 2 passed by four months later and found that six of the eight were still erupting.

18. Io’s surface is exceptionally smooth, any cracks are filled in by molten lava. It has a thin atmosphere of SO2.

19. Io’s volcanic activity produces the Io Plasma Torus, a donut-shaped region of energetic heavy-ions that follows Io’s orbital track.

21. The Io plasma torus encircles Jupiter and has lethal radiation levels.

22. The source of Io’s energy is Jupiter’s pull of gravity
The source of Io’s energy is Jupiter’s pull of gravity. It pulls more on the part of Io that is close to Jupiter and less on the part further away.

23. Europa’s gravitational pull on Io causes Io’s orbit to be non-circular and non-synchronous.

24. This difference in pull causes internal upheavals in Io and this friction produces the excess energy that causes the volcanic activity.

26. Europa - Networks of crisscrossing lines over bright clear fields of water ice. The lines may be cracks in the ice. Europa has few craters.

30. Ganymede & Callisto - Both have much ice throughout
Ganymede & Callisto - Both have much ice throughout. Ganymede is the largest moon in the solar system. It is larger than the planets Mercury and Pluto.

31. Ganymede has many impact craters (maybe even highlands and maria)
Ganymede has many impact craters (maybe even highlands and maria). It also has grooves and ridges.

36. Callisto has a series of concentric ridges surrounding two large basins.

38. Callisto Valhalla impact crater

39. Callisto Scarp

40. Jupiter has rings. They are not as large or prominent as those of Saturn.

41. They were discovered by the Voyager missions, but were predicted by many astronomers.

45. Shoemaker-Levy 9 impacts

51. G impact projected on Earth