LECTURE 19: MOONS OF THE JOVIAN PLANETS
- How did the Jovian planets get their moons?
- What makes Io the most volcanic world in the solar system?
- What makes Europa one of the most likely sites for life in the
- What are the key differences between the inner Galilean
satellites (Io, Europa) and the outer ones (Ganymede, Callisto)?
- What are the unique properties of Saturn's moon Titan?
- The Jovian planets all have many moons.
- Large ones (comparable to or bigger than Earth's moon) are:
- Four Galilean satellites of Jupiter.
- Saturn's moon Titan.
- Neptune's moon Triton (smaller than Earth moon).
- Small moons go down to ~ 10 km across (like moons of Mars).
- Unlike Earth's moon, origin of Jovian planet moons thought to be
joint formation (in some cases) or capture (in others).
- Staggering diversity of surface features, shaped by impacts
and by tidal heating from planets.
THE GALILEAN SATELLITES OF JUPITER
Density (kg / m3)
- Period ratio of inner 3 planets is 1:2:4.
- Ganymede is most massive satellite in solar system.
- Densities imply Io, Europa largely rock, Ganymede, Callisto more ice.
- Surfaces of Io, Europa show many signs of geological activity;
Ganymede, Callisto appear relatively quiet.
GALILEAN SATELLITES: DISTINCTIVE PROPERTIES
- Io: Most volcanic world in the solar system.
- See eruptions, constantly changing surface coloration.
- Volcanos powered by tidal heating of moon's interior.
- Jupiter's tidal gravity stretches Io, strongest when Io is closest.
- Regular tugs from Europa and Ganymede move Io in and out,
so Io is constantly flexed, heated.
- Europa: Icy surface, ocean beneath?
- Level surface of water ice, with network of fractures.
- Tidal heating probably responsible for fractures and surface activity.
- Models of structure, magnetic activity suggest a subsurface ocean
of liquid water with dissolved minerals.
- Europa may be likeliest site of ongoing life in solar system
- Ganymede and Callisto: Heavily cratered, icy surfaces.
- Relatively little geological activity, though more than Earth's moon.
- Largest moon in solar system after Ganymede.
- Density suggests mixed rock/ice composition.
- Only moon with substantial atmosphere.
- Opaque haze.
- Surface pressure ~ 1.5 x that of Earth's atmosphere.
- Composition 90% nitrogen, most of rest methane (CH4).
- Surface could have seas of liquid methane and ethane
- Huygens probe, released from Cassini spacecraft, landed on
surface of Titan in January, 2005.
- Images suggest channels carved by flows of liquid
on surface. Methane rain? Still being analyzed.
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Updated: 2005 May 22[dhw]