1. Moons of Jupiter
The bodies in orbit around Jupiter make up a miniature version of the Solar System _
The four largest moons, the Galilean moons, are much larger than the others and are some of the most interesting bodies in the Solar System

2. The Innermost Moons
The four innermost moons of Jupiter are small and irregularly shaped
All orbit very close to Jupiter, within 250,000 km of Jupiter's cloud tops _
Amalthea
Thebe
Metis
Adrastea
~40 km
~20 km
~100 km
~260 km

3. The Galilean Moons
The next four moons in orbit around Jupiter are the large Galilean moons _
Ganymede is the largest moon in the Solar System and is actually larger than Mercury
We will talk about each of these worlds in more depth later Io
Europa
Ganymede
Callisto

4. The Others
Over the past decade, technology for Earth-based telescopes has increased enough to spot many small moons around Jupiter _
The current count is ~63, but better technology will keep this number increasing
Can you find the moon?

5. Moons or Captured Asteroids?
While the four Galilean moons have roughly circular orbits, most of the others are highly eccentric
It is believed that the majority of these moons are actually asteroids or comets captured by Jupiter's gravity _

6. A Mini Solar System?
The early formation of Jupiter may have mimicked the formation of the Solar System as a whole _
The larger Galilean moons would have slowly grown and accreted much like the inner planets of the Solar System
Artist conception of an early Jupiter

7. A Mini Solar System?
Io, the closest to Jupiter of the Galilean moons, has a large core made of iron and iron sulfide _
As distance from Jupiter increases, the cores become smaller and the material becomes less dense and more icy

8. Io Io orbits Jupiter at a distance of 422,000 km _
Detailed images from Galileo showed a 'pizza crust' like surface
Surprisingly, the Voyager probes and Galileo both observed dozens of active volcanoes on the surface

9. Volcanism on Io
The eruptions appear to be mainly sulfur compounds, though some molten rock may be present _
The surface is so young that essentially no impact craters exist
A thin atmosphere of sulfur dioxide is present due to the volcanic eruptions

10. Source of Volcanism _
Io's close proximity to Jupiter creates huge amounts of gravitational stress
Interactions with other moons, mainly Europa and Ganymede, add to the constant squeezing of Io

11. Io's Plasma Torus _
Many atoms are stripped from Io's atmosphere (mainly sulfur) and swept out around Jupiter
This forms a thick ring of energized particles around Jupiter

12. Europa _ Europa is 0.65 times as massive as the Moon
Europa's surface appears completely different from its neighbor, Io
The light colored surface has relatively few craters and many large cracks

13. A Water Ice Surface _
The cracks form in areas where the crust has split apart, allowing material from below to rise to the surface
Like Io, tidal interactions with Jupiter and other moons generate interior heat

14. A Vast, Living Ocean?
Many pieces of evidence lead to the belief that Europa may have a huge ocean underneath the ice layer _
Such a large amount of liquid water would provide ideal conditions for life to develop

15. Ganymede Ganymede orbits Jupiter at a distance of 1,070,000 km
It is 2.02 times more massive than our Moon and larger than Mercury _
Ganymede's density reveals that it is made of more ice than the other two, and is much less active
Enhanced color image of Ganymede

16. Surface of Ganymede _
On Ganymede, however, the dark area represent older, more cratered material while the lighter is younger, fresher ice

17. Activity on Ganymede _
Close examination of the surface does reveal evidence for ancient lava flows and possible plate movement
Ice wrinkles and cracks on the surface represent either splits or collision of material in the crust

18. Callisto Callisto orbits Jupiter at a distance of 1,888,000 km
Callisto is 1.46 times more massive than the Moon _
Like Ganymede, Callisto has a large amount of ice throughout the surface and interior

19. Callisto Surface Features
Two large craters show a rippling pattern around them
This was most likely caused by a melting then quick re-freezing after impact _
Callisto has not evolved since its initial formation, making it one of the oldest surfaces in the Solar System

20. Future Visits? _
The mission ended in 2003 when the spacecraft was intentionally crashed into Jupiter
There is a lot of talk about future missions to the Galilean moons, especially Europa
Funding is currently being concentrated toward manned spaceflight to the Moon and Mars

21. Cool Pic Io
Europa