You might think that the moons of a planet are all alike -- but the opposite is true. We want
to study features on the surface, like mountains, valleys, lava flows, and craters. Is the surface
rock or ice -- and what kind? The information helps scientists write the history of each moon,
and figure out why a particular moon looks the way it does today. Galileo's camera gives us
stunning visual images of these strange worlds, with their volcanoes, craters, or icy terrain.
The NIMS
identifies the minerals that make up the surface.
What is the texture of rocks and ice on the surface? Is the surface hard ... or loose.... sandy...
fine-grained.... clumpy? The PPR
determines the size of crystals on the surface by looking at light that has been polarized by these
crystals. Polarization can reveal information about the nature of the object that is reflecting the
light. We take advantage of it on Earth by wearing sunglasses with polarized lenses that give a
"cool" view of brightly lit objects.
What is the environment on the surface of a moon like? Is it hot, or cold? And how hot or
cold? By measuring the infrared light emitted from the surface, NIMS and the PPR can take a
moon's temperature.
Next: Observing Magnetic Fields 
