Turbulence and its transport in astrospheres

Project Description: 

The radiation environment of an exoplanet, situated as it is within the astrosphere of its host star, this region being that dominated by plasma originating from said star, can play a significant role in its potential habitability. Galactic cosmic rays and stellar energetic particles have increasingly been recognised as playing a considerable role in this radiation environment, and as such their transport within astrospheres often vastly different to our own heliosphere has become the subject of considerable recent study. This transport, however, depends strongly on these particle’s diffusion coefficients, which in turn depend on the turbulence properties of astrospheric magnetic fields. Here, alas, lies the rub: although considerable observations, and magnetohydrodynamic simulations, exist for the large-scale plasma parameters (such as e.g. the stellar winds) of exoplanet-hosting astrospheres, no observations exist for turbulence parameters. This is no surprise, as it is difficult to resolve something relatively small at great interstellar distances. One approach to modelling these essential model input parameters, which are also of great interest to the broader community in and of themselves, would be to use turbulence transport models (TTMs) derived in the heliospheric context. Of these, several have been proposed, which sometimes make very different predictions in the heliosphere. The aim here is to investigate the predictions of three different TTMs in an astrospheric context, in order to calculate and compare resulting diffusion coefficients from theory, thereby to ascertain whether their use could in principle lead to different conclusions when employed in an energetic particle transport model. These models would be the simplified single component model of Zank et al. (1996), and the more complex two-component model of Adhikari et al. (2017). The first of these you will code and solve yourself, while for the latter you will be provided with a pre-existing, FORTRAN-based solver. These you will adapt to the astrosphere of kappa Ceti, and compare with the results computed with a separate TTM by Engelbrecht et al. (2026). A standard set of diffusion coefficients will then be calculated from first principles, and again compared with prior work. Note that advanced programming and mathematical skills are imperative for this mission.(NWU)Advanced mathematical AND programming skills.

Supervisor

North-West University (NWU)

Co-Supervisor