GALILEAN MOONS OF JUPITER:
Exploration of remote worlds

Introduction to the Galilean moons

Slide 3

Selected topics on moons,
magnetism, oceans.

Measurements of small changes of the velocity of a spacecraft flying by a moon provides information on the distribution of matter in the interior. 
We know that all the moons are denser near the center, but we don’t know if there are two or three layers
And there is no direct information to show if the matter within these moons is hot or
      cold, solid or liquid.

State of matter

Ganymede’s internal magnetic field:
A surprise!

Slide 8

Source of stable internal magnetic field?

Implications for present state & thermal evolution

Ganymede’s mini- magnetosphere

Ganymede’s mini-magnetosphere controls the motion of energetic charged particles.
  Notice that the red  
  lines connect to
  Ganymede at both
  ends. 
The blue-green lines in the polar regions connect only once.  Their other ends are on Jupiter.
  These lines direct
   energetic charged
          particles to the
          surface near poles.

Impacts of energetic particles guided along the magnetic field damage the ice grains.  Images show differences between polar ice where the field connects to Jupiter and lower latitude ice.

Looking for oceans

"There have been speculations about..."

Chaos (Conamara Region) at Europa

A trip over Europa

If there is a subsurface ocean with some dissolved salts or acids -

Slide 19

Test of induced field

Near surface conductor
is required

Ganymede also shows signs of water-intrusions.  Smooth young terrain appears surrounded by heavily cratered or otherwise ruptured terrain

The Galileo magnetometer found evidence of a layer of melted water beneath Ganymede’s icy surface

You have seen these one of these images before. Here I show the way the magnetosphere appeared on multiple passes as Jupiter’s field rocked back & forth.
G1, G2 occurred in 1996.  The induced field test required a pass with the field pointing the other way.  G28 in May 2000 gave us the opportunity!

But there was a problem.  Ganymede’s fingerprints are almost hidden by its permanent internal field

Ganymede has a strong permanent field.  If there is a global ocean beneath the surface, the poles would rock back and forth just a bit as Jupiter’s field shifts

The most probable values given by our analysis would be expected if:

Why might a melted layer be present somewhere inside of Ganymede?

The inductive response

Probably all three icy moons have buried oceans

Let me beat you to it!

Galileo and Jupiter’s moons