Fundamentals of geophysics The solar system originated more than 4.5 billion years ago from a rotating cloud of molecular hydrogen and interstellar dust surrounding a star that became the Sun. Collisions and coalescence of particles in the dust cloud led to the formation of a solar system with eight planets and countless smaller bodies that has fascinated mankind since prehistoric times. Our knowledge of the solar system exploded in the recent era of space exploration and its complete description deserves a library on its own. This chapter provides brief descriptions of the orbits and physical properties of the major planetary bodies. These exhibit natural phenomena originally studied on Earth such as gravitational and magnetic fields seismicity and tidal motions. They can be understood with geophysical concepts and techniques introduced in later chapters