Current limitations in chemical abundance measurements for M dwarfs and implications for exoplanet characterisation

Planets are assembled from the same material as their parent stars. Therefore, stellar chemical abundance measurements provide important constraints on the formation, composition, and interior structure of exoplanets. M dwarfs are the most prolific hosts of low-mass, rocky, potentially habitable exoplanets. However, owing to the complexity of their atmospheres (which are marred by molecular absorption), elemental abundances of M dwarfs are notoriously difficult to measure. For key rock-forming elements, state-of-the-art abundance precisions attainable from high-resolution spectroscopy of M dwarfs can be up to an order of magnitude poorer than that for sun-like stars. This would mean a comprehensive characterisation of planets around M dwarfs may be more elusive. We explore examples of consequences for uncertainties in exoplanet modelling, such as condensation sequences, bulk compositions, and core-mantle fractions. We discuss what is required from the stellar science community to make progress.