Abstract EANA2025-53

Stars and their accretion disks form from the same molecular cloud. Therefore, the composition of a star can serve as a first approximation of the upper limit of its accretion disk’s composition. Using only the host star’s metallicity and the temperature in the disk related to the distance to the star, our model swiftly estimates the composition of planetary building blocks. Unlike more complex models such as GGChem our model prioritizes speed and simplicity and yet, it agrees well with them for C/O ratio  < 1.  Hence our model provides  a fast, accessible first-order approximation that can be easily integrated into other models (e.g. sophisticated interior structure models). 

As a first demonstration of the the model’s practical application, we estimated the  composition of the TRAPPIST-1 planets. Then, using an interior structure model employing look-up tables created with Perple_X for thermodynamic properties of the silicate mantles, we show that it is possible to predict the core mass fraction and radii for the inner planets, which agree well with the observed values from Agol et al. (2021). The findings suggest that the outer planets should have a maximum water fraction below 20 wt% to match their observed radii.

Here we show first results of parameter study using an improved version of our composition model, now incorporated FastChem for the chemical equilibrium,  to illustrate how strongly the composition of ultra-short-period planets, those orbiting very close to their host star, can differ from that of “Earth-like” planets, and how these compositional variations could affect a planet’s interior structure.