Tidally-distorted, rocky exoplanet interiors and transit lightcurve simulations: Application to GJ 367b using JWST observations

Ultra-short period (USP) rocky exoplanets present an exciting opportunity to constrain planet compositions using a combination of observations and modeling. In previous published work, we computed tidally-distorted, three-dimensional interior structure models of planets with iron cores and silicate mantles to predict a lower limit for the iron content of USP planets, including KOI-1843.03, an exo-Mercury planet candidate with the shortest known orbital period (4.2 hours). We present an improved planet interior structure modeling code coupled to a raytracing module that can compute transit lightcurves for simulated planet shapes. We have also developed an efficient code for approximating transit lightcurves of triaxial ellipsoids, appropriate for use in numerical fitting procedures. We apply this second code to the JWST white lightcurve of GJ 367b, demonstrating its use in conjunction with nested sampling to constrain the shape of GJ 367b. Finally, we combine constraints from lightcurve fitting and interior structure modeling to draw conclusions on the composition of GJ 367b.