Spatially resolving the chemical composition of the planet building blocks

The inner regions (0.1-10 au) of protoplanetary discs are the expected birthplace of telluric planets. In those hot regions, solids can experience cyclical annealing, vapourisation, and recondensation. Hot/warm dust grains emit mostly in the IR, notably in N-band (8–13 ?m). Studying their chemistry with the new MIR VLTI instrument MATISSE, which can spatially resolve those regions, requires detailed dust chemistry models. Using radiative transfer, we derived IR spectra of a fiducial static disc model with different inner-disc (<1 au) dust compositions. The latter were derived from condensation sequences computed at LTE for three initial C/O ratios: 0.4 (subsolar), 0.54 (solar), 1 (supersolar). The three scenarios return very different N-band spectra that MATISSE should be able to discriminate. From that, we propose a first interpretation of N-band 'inner-disc' spectra obtained with the former VLTI instrument MIDI on several YSOs, and show recently obtained MATISSE N-band spectra.