Presentation #600.11 in the session Planet Detection - Transits.
The rotation of a planet causes it to bulge at its equator due to centrifugal forces. Saturn, which is about 10% larger around its equator than at its poles, is an example of planetary oblateness in our own Solar System. This oblateness in an exoplanet can manifest as deviations from a perfectly symmetric transit light curve, with the specific shape depending on the exoplanet’s rotation rate, interior structure and spin-orbit alignment. We introduce an open-source semi-analytic transit model that incorporates planetary oblateness implemented in the Jax framework. The implementation is not only faster and more precise than equivalent numerical models, but is also automatically differentiable. Leveraging this differentiability, we investigate the information content of oblateness in transit light curves with Fisher information analysis, which allows us to quantify the sensitivity of the transit light curve to exoplanetary oblateness and spin-orbit alignment. We also quantify the biases in transit parameters when circular planet models are fit to transit light curves of oblate planets. Current and future observations with JWST are precise enough to be able to probe this effect for the first time on Jupiter-like exoplanets which are not tidally synchronized, which will be amenable to constraints from our new model.