The interior structure of terrestrial planets : an application to Mars

(eng) The Earth's interior structure is well known from seismic experiments. From them we precisely know the size and state of the core and the density and rheological properties within the planet. This information, complemented with rock sample analysis, has been used to constrain the thermal state of the Earth and deduce the composition of the mantle and the core. By contrast, we know very little about the interior structure of other terrestrial planets. Our knowledge is limited to the bulk properties - such as the average densities and moment of inertia (except Venus) - and the fact that they all have at least a partially liquid core. Their composition and thermal state are only weakly constrained. With the aim of elucidating the interior structure, we construct detailed interior structure models applicable to terrestrial planets. We then show how knowledge of the model parameters can be inferred from the data provided by space missions, earth-bound measurements, and laboratory experiences from high pressure physics. As a case study, we infer the model parameters for two different data sets related to the planet Mars. The main aim of the first study is to constrain the state, size, and composition of the core by using existing geodesy data. In this study we do not infer the thermal state and mineralogy of the mantle but use results that have been obtained from independent studies relating to the thermal evolution and composition of Mars. The objective of the second study is to ascertain whether the mineralogy and the thermal state of the Martian mantle can be inferred by combining geodesy, seismic, and magnetic induction data. The first study shows that Mars has no solid inner core and that the liquid core contains a large fraction of sulfur. The absence of a solid inner is in agreement with the absence of a global magnetic field. We estimate the radius of the core to be 1616 +/-137 km and its sulfur concentration to be 12+/-6wt%. We also show that it is possible for Mars to have a thin layer of perovskite at the bottom of the mantle. The second study shows that the temperature of the mantle and its mineralogical composition can be determined with a high confidence. The robustness of our method is also tested by using incomplete and missing data sets.