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The Spacecraft
Observing Surface of Moons

NIMS Observation of Europa
NIMS Observation of Europa

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.

Infrared image of Europa taken with Galileo's PPR instrument
This infrared image of Europa, showing heat radiation, was taken with Galileo's PPR instrument

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.

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Mission Operations