Elemental abundance retrievals in planet-forming disks: links to embedded protoplanets

In the 2020s, the exoplanet field will move increasingly towards planetary composition studies. One of the key aspects is to link planetary elemental abundances to their formation history in disks. Measurements of gas-phase elemental abundance ratios (e.g., C/O) in planet-forming disks are needed for formation models to reliably predict planetary chemical compositions. This is increasingly timely, with the growing interest in chemical diagnostics of planet formation, biomarkers, and rapid progress in exoplanet atmospheric retrieval data and methods. In planet-forming disks so far, elemental abundance measurements have been done with very coarse spatial resolution (average abundance ratios over 10s-100s of au scales) and through a cumbersome process of running a handful (maximum of order 100) complicated models to be fitted, essentially by hand, to a variety of continuum and line data from (sub-)millimetre telescopes (APEX, IRAM, ALMA, etc.). This means our understanding of degeneracies in the methods, optimal data acquisition, and true uncertainties in the derived abundances in disks is poor compared to the state of the art in exoplanet studies. We are now identifying gaps in disk gas and dust, and associating embedded protoplanets with them, with growing confidence. ALMA is allowing us to obtain unprecedented chemical composition data on ~10au scales. It is quickly becoming essential to adapt our disk-averaged abundance measurement techniques for small scales, to study gas in the vicinity of specific protoplanets and to test increasingly complex but poorly constrained disk elemental composition models. These advances will be key to unlocking the impending flood of JWST and Ariel exoplanet composition data. In this project, you will have an opportunity to exploit new data and develop methods to advance the cutting edge of disk and planet composition links.