Asteroid and comet exploration
Exploration of Venus, Mars, and the Moon have had two major scientific objectives. One was to clarify the processes which control planetary evolution. The fulfillment of this purpose, although far from complete, was eminently successful in generating entirely new perspectives on the growth and differentiation of earth. The second objective, particularly prominent in the planning of the lunar exploration, was to augment the understanding of the virtually unknown preplanetary history of the solar system. This would include the fundamental questions of the origin, emplacement, and state of matter gathered around the sun and some planets. Preplanetary history also inquires into the problems of fractionation, condensation, and non-gravitation aggregation of circumsolar and circumplanetary matter.