Images of the surfaces of the Galilean satellites, or of any planets in the solar system, reveal a general history of the planet, and the state of the planet's interior through time. For example, volcanoes require a hot interior. If we know from looking at images of a planetary surface that the last period of volcanism was hundreds of millions of years ago, we know that the interior of the planet must have been hot until that time. This type of information helps to constrain models of the interior structure and evolution of the satellites, as well as provide information about their formation.

This set of activities has shown the wealth of information obtainable from the simplest black and white images of a planetary surface. Much of the first wave of reconnaissance of the solar system was done in just this way, with scientists working to understand the little information they had from the early planetary spacecraft. The Galileo spacecraft, which will remain in orbit in the Jovian system until late 1997, not only has a camera capable of taking black and white images of the surfaces of the satellites, but also has a wealth of other instruments to augment this information. The camera has filters in six different colors, allowing color images to be taken and analyzed. This can yield valuable information about the chemical composition of surface materials. Other instruments on Galileo allow it to measure properties of Jupiter and its satellites at a variety of near infrared wavelengths, investigate the radiation and magnetic environments, and obtain more precise measurements of the sizes and densities of the satellites. Galileo's two-year tour through the Jovian system should provide information for scientists to study for years to come.


Sources: Some information in this module was adapted from Craters: A Multi-Science Approach to Cratering and Impacts, by W.K. Hartmann and J. Cain. A Joint Project of the National Science Teachers Association, The Planetary Society, and NASA. Published by the National Science Teachers Association, 1995.

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This module was written by Cynthia Phillips, Dept. of Planetary Sciences, University of Arizona, Tucson AZ, and funded in part by the NASA Spacegrant program.

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