Gravity, rotation, and interior of the terrestrial planets from planetary geodesy: example of Mars

Abstract

Information on planetary interiors can be obtained from planetary geodesy measurements of global parameters such as the gravity field and the rotation variations (including precession). These properties can be derived from radio science experiments in which Doppler shifts of radio signals between the Earth, planetary landers, and orbiters are measured. A radio link between the Earth and one lander on Mars has been successfully used to constrain the rotation and the precession, and consequently to obtain the moment of inertia of the planet, the global mass repartition, and its seasonal variations. A radio link between the Earth and one orbiter has also been used to determine the gravity field and its time variations. In particular, the tidal Love number k 2 has been determined, from which the Martian core has been shown to be at least partially liquid. New missions that involve a space geodesy experiment addressing these topics are presented. A network of landers could probe the interior of the planet through seismic monitoring, magnetic sounding, and measurements of its rotational dynamics by radio science. This would allow the determination of the overall interior structure, including crust, mantle, and core divisions, and the state of the core (liquid/solid, density). Also composition, mineralogy, density, and temperature profiles could be inferred. Information on the interior of terrestrial planets (and large moons) other than Mars has also been determined by using radio tracking of an orbiter. For example, the tidal Love number k 2 of Venus was deduced from Magellan's radio science experiment. Future missions such as Messenger and BepiColombo have dedicated onboard planetary geodesy instruments and will provide improved information on the interior of Mercury from Doppler measurements. © Springer-Verlag Berlin Heidelberg 2007.