Towards Constraints on Morning and Evening Terminators of Distant Worlds with TESS

We present preliminary results on a search for differing morning and evening limbs of giant exoplanets observed in transit with the Transiting Exoplanet Survey Satellite (TESS). Transmission spectroscopy has been one of the most lucrative techniques in allowing us to probe exoplanetary atmospheric compositions. This approach takes advantage of the minute, fractional dimming of stellar light as an orbiting planet passes in front of the host star, where stellar radiation filters through the planet’s gaseous envelope. Driven by atomic and molecular opacities in the atmosphere, this method measures the wavelength-dependent size of the exoplanet to infer its atmospheric composition. A common assumption of this methodology is that the atmosphere is homogeneous, with single gas abundances, cloud composition, and a consistent temperature-pressure profile in its entire limb. These simplifications disregard exoplanets as three-dimensional objects predicted to give rise to differing properties at the limbs, impacting key inferences made through their compositions, such as formation mechanisms and/or interior structures. Building upon previous work that asymmetric limbs could be observationally detected using the ingress and egress of transit, we show the first results of a project that aims to search for these spectral signatures using precise light curves from TESS. Our work, which provides the first constraints on the magnitude of morning and evening limb differences, will prove to be fundamental in vetting the best targets for further characterization with observations from telescopes like the James Webb Space Telescope (JWST). We also discuss ongoing efforts on expanding our approach to a larger (~100 giant exoplanets) sample size, which will enable us to explore population-level effects among transiting gas giant exoplanets.