Ph Defense

Shivangi SHARAN

"The interior of planets as characterised by their magnetic fields : the Jovian and Martian cases"

Monday, January 30th at 2 p.m. - LPG - Building 4 - Faculty of Science and Technology - Nantes University

Abstract : We study the magnetic field of Mars and Jupiter to obtain information about their interior from them. There are internal and external sources of magnetic field around a planet which can be modelled using Spherical Harmonics (SH). The internal sources are the dynamo, crust and induced fields while the external sources are produced outside the planet due to interaction with solar phenomena. For Jupiter, we work with the internal dynamo field using Juno satellite data while for Mars, we work with the induced fields using data of two satellites, MGS and MAVEN.

Jupiter’s dynamo field is produced due to convection in the conducting liquid metallic hydrogen and undergoes changes with respect to time called secular variations (SV). We model the internal field and its changes up to SH degree 16 and 8 respectively. From them, we decipher the depths of field generation at 0.83 times the radius of the planet. The SV varies at a rate of about 0.6% per year and is dominantly produced by the advective movements of the fluid. The field maps display two prominent flux patches while the SV maps display zonal and non-zonal features.

Mars presently does not possess a dynamo but is governed by crustal fields that are at least twice the order of magnitude than that observed on Earth. The residual fields obtained after removal of the static crustal fields are of the order of 10 2 nT. Their analysis provides a 27 days trend that can be used to obtain magnetic indices. The residual fields are then modelled up to SH degree 3 for its two components- the externally inducing and the internally induced fields. From them, we get some information about the conductivity of the interior using Bayesian inversion.

PhD supervisor : Benoit LANGLAIS, CNRS researcher