Encadrant : Mark Wieczorek

Lieu : Laboratoire Lagrange (Mont Gros)

Site web : http://www.ipgp.jussieu.fr/ wieczor/

Résumé du projet :

The strong, outermost portion of a planet is conventionally referred to as the lithosphere. When loads are emplaced on the lithosphere, such as in the form of volcanoes, magmatic intrusions, or plumes, the lithosphere flexes, with the amount of flexure being controlled by the lithospheric strength. The mass of the load and the associated lithospheric deflections give rise to both gravitational anomalies and topographic relief. By using gravitational and topographic data acquired from orbiting spacecraft, it is possible to place constraints on not only the density of the load, but also on the thickness of the lithosphere and how it varies laterally across the surface of a planet.

The thickness of the lithosphere is often quantified by the thickness of an equivalent elastic shell that overlies an inviscid fluid. The elastic thickness is an important quantity for understanding a planet as it is controlled by the planet’s internal temperature profile at the time the load was emplaced. Given that the thermal evolution of a planet varies in both space and time, maps of the elastic thickness can be used to constrain the evolution of the planet. Heat flow estimates obtained from gravity and topography data can be compared with in situ measurements, and the density of volcanic loads can be compared with estimates based on remote sensing data, samples, or meteorites.

This M2 topic aims to investigate the lithosphere of Mars using global gravity and topography data determined by recent and historical spacecraft missions. The results will be interpreted using recent thermal evolution models of the planet. Though such investigations were performed previously, this project will make several important new contributions.

First, modern multitaper spectral analysis techniques developed in spherical coordinates will be employed. Second, improved lithospheric loading models will be used. Whereas most previous models have made the simplifying assumption that the surface and subsurface loads were either perfectly in phase, or statistically uncorrelated, we will develop a model that takes into account a statistical correlation of the two loads. Third, this work will make use of the most recent gravity and topographic models of Mars. The gravity field of Mars has been improved substantially since many of the initial works were published, and higher resolution gravity models should allow for improved estimation of the elastic thickness.