The magnetic fields of terrestrial Exoplanets

Mahesh Herath ( Université McGill )

The ability to generate a sustainable magnetic field is an important aspect of planetary habitability. In this work, we outline the deployment of a planetary interior structure model to determine the optimal conditions that could potentially generate magnetic fields in terrestrial Exoplanets. An assumption was made that the magnetic field is created in a manner similar to that of the Earth’s, where convection from the release of light elements during the formation of a solid Iron inner core inside a liquid Iron outer core leads to the emergence of a geodynamo. The models were tested on planet masses ranging from 1 Mearth to 6 Mearth, with their core mass fractions (CMF's) varied from 16 percent to 70 percent. The simulations predict that planets between 1 Mearth and 3 Mearth generate their strongest and longest  lasting fields at CMF's between 30 percent and 50 percent while the field gets damped at CMF's above 50 percent. Planets with masses between 4 Mearth and 6 Mearth have their strongest fields for CMF’s between 16 percent and 50 percent. Planet masses between 2 Mearth and 4 Mearth, with CMF's between 30 percent and 50 percent showed the most stable magnetic fields over all the simulations. It was also noted that while CMF’s above 50 percent would damp any emerging geodynamos, a slight increase in the thermal conductivity of the core-mantle-boundary layer would solve that problem and generate sustainable magnetic field over several billion years. This showed overall that planetary masses, CMF’s and the thermal conductivity of the deep interior layers are important aspects in the evaluation of a rocky planet’s ability to have a magnetic field.