Planets have excited the minds of man since prehistory. In our own time planetary science has become a rapidly developing area of astronomical research, as the instruments carried by spacecraft have vastly increased our knowledge of planetary surfaces and interiors. the rocky planets of the inner solar system bear countless craters, scars of their encounters with innumerable meteorites, although the active surface of the earth has contrived to erase these features from our own planet. The outer giants, particularly Jupiter, have vigorous atmospheres, while Io, a satellite of Jupiter, has sulphur volcanoes. In this book Alan Cook explains how the mechanical properties of the planets are determined, how planetary materials behave at high pressure, and how celestial mechanics and the quantum physics of highly condensed matter may be combined to determine the general constitution of the planets.