Earth physics: State-of-the-art and main issues

The state of the art and main issues concerning Earth physics are discussed. Many geophysical processes result from the interaction of the various parts of the Earth system, the solid Earth, the atmosphere, the oceans, the liquid core and the solid inner core which exchange energy and angular momentum among themselves. Study of these phenomena on a global or on a local scale provides substantial insight into the properties of the Earth itself. The phenomena associated with the geoid are the rotation about its axis of spin (or its time derivative), the polar motion (mutation and precession), tides, temporal variations in its mass distribution, and its geopotential. These are caused by the deformation of the solid Earth and by the exchanges of angular momentum both between the solid and fluid parts with extraterrestrial bodies. Space geodesy will contribute in a substantial way to understanding of the long term dynamics of the Earth, such as the relative motions between the major tectonic plates, the deformation in active tectonic zones and stress accumulation and release on large faults. The possible contribution of space techniques to research in this field is discussed and recommendations for spaceborne instrumentation are given.