Space Science in the Twenty-First Century: Imperatives for the Decades 1995 to 2015 -- Copyright -- Foreword -- Contents -- 1 Introduction -- 2 Scientific Goals and Recommendations -- GOALS OF PLANETARY EXPLORATION -- To understand the origin of the solar system. -- To understand the evolution of the planets. -- To learn what conditions lead to the origin of life. -- To learn how physical laws work in large systems. -- A BALANCED PLANETARY PROGRAM -- A MARS FOCUS -- SUMMARY OF RECOMMENDATIONS -- Scientific Investigations -- Technical Developments -- International Collaboration -- 3 Status of Planetary Science in 1995 -- OVERVIEW -- State of Planetary Exploration as of 1995 -- Scientific Questions as of 1995 -- PLANETARY GEOSCIENCES -- Scientific Objectives for Planetary Geosciences -- Formation -- Interior Structure, Dynamics, and Physical State -- Crustal Evolution -- Planet Morphology and Surface Processes -- Measurement Objectives -- The Inner Solar System -- The Moon -- Mercury -- Venus -- Mars -- Internal Characteristics of the Inner Planets -- Magnetic Fields of the Inner Planets -- Atmospheric-Climatic Connections of the Inner Planets -- Rocky Satellites -- Satellites of Jupiter -- Satellites of Saturn -- Satellites of Uranus and Neptune -- ATMOSPHERES -- Earth, Mars, and Venus -- Titan -- Io and the Plasma Torus -- Jovian Planets -- RINGS -- INTERIORS OF THE GIANT PLANETS -- PLANETARY MAGNETISM -- Generation of Planetary Magnetic Fields -- Earth's Magnetic Field -- Studying Planetary Magnetic Fields -- PRIMITIVE BODIES AND THE ORIGIN OF THE SOLAR SYSTEM -- The Origin of the Sun and Planets -- Search for and Study of Other Planetary Systems -- Asteroids, Small Satellites, and Meteorites -- General Characteristics -- Anticipated State of Knowledge in 1995 -- COMETS -- General Characteristics -- State of Knowledge in 1995.

Questions in Cometary Science -- Comet Measurements and Technical Requirements -- 4 Future Programs -- PROPOSED MISSIONS -- Programs for Planetary Geosciences -- Types of Missions -- Planned Missions -- Programs for the Outer Solar System -- Types of Missions -- Planned Missions -- Future Missions and Programs for Primitive Bodies and the Origin of the Solar System -- A PROGRAM FOR INTENSIVE EXPLORATION OF MARS -- Why Mars? -- Scientific Objectives for a Mars Focus -- Role of Humans in Intensive Mars Exploration -- A Phased Approach -- RECOMMENDATIONS -- Exploration of the Solar System -- Exploration of Mars.