In Class:
Question to Ponder
What is the order of the Galilean moons from inner (i.e., closest to
Jupiter) to outer?
- a) Callisto, Europa, Io, Ganymede
- b) Io, Callisto, Europa, Ganymede
- c) Io, Europa, Ganymede, Callisto
- d) Io, Ganymede, Europa, Callisto
Europa
- very smooth surface -- almost no craters
- Gets hit just about as often as Ganymede and Callisto, so it must repair
its surface.
- Surface may be water ice overlaying a subsurface ocean
- Impacts make holes through which liquid water floods and then freezes
into a flat surface.
- Celestial zamboni.
- Ice rafts suggest that the icy surface moves around (i.e., it floats on
this subsurface ocean.
- Creates a sort of plate tectonics, though the plates appear to be very
small.
- Because the ocean may be liquid water, and because it's protected from
the nasty stuff in space by the icy crust, many people think that life might
have arisen here.
- NASA and other space agencies have comtemplated missions to go
find out, but it's tough because not only do you have to get to
Europa, but you've got to drill through the crust.
Io
- the "pizza" planet.
- No ice here -- only volcanoes spewing molten sulfur onto the surface.
- Entire surface is repaved on 1 MYr timescales.
- Has high density -- mostly rock.
Tidal Heating
- Interactions between Jupiter's gravity and the gravity of the passing
moons squishes Io's interior.
- Creates frictional heating that makes the interior molten and drives
the volcanoes.
- Europa experiences a similar effect, but because it's farther from
Jupiter, the heating is less.
- Europa's interior is heated so that the ice melts into liquid.
- Ganymed and Callisto are affected to a far lesser degree.
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