The Comet Nucleus Tour, or CONTOUR, mission was to study two very different comets as they made their periodic visits to the inner solar system. It was the first mission designed to study both the physical and chemical properties of comets.

At each comet flyby, the spacecraft was to get as close as 60 miles to the comet nucleus to capture high resolution pictures, perform detailed compositional analyses of gas and dust, and determine the comet's precise orbit. This information would dramatically improve our knowledge of comet nuclei and their diversity.