Planetary exploration: scientific importance and future prospects

Study of planetary bodies by direct exploration using robotic and manned spacecrafts is a frontier area of research. Many nations are planning missions to the moon during the next two years and to other planets in the coming decades. These plans include establishing permanent human presence on the moon and Mars sample-return mission by 2015. The Indian Space Research Organization is also formulating a long-term plan of planetary exploration. Chandrayaan-1, an unmanned orbiter mission to the moon is in an advanced stage of implementation, slated to be launched in 2008. The possibility of manned space missions is also being debated. I discuss here the scientific merits of missions to various planetary bodies in the solar system and evaluate the priorities. Missions to moon, Mars, Mercury and Galilean satellites of Jupiter appear scientifically most exciting. A direction for future planetary exploration is outlined