TRAPPIST-1h as an ExoTitan: The role of assumptions about atmospheric parameters in understanding an exoplanet atmosphere

The TRAPPIST-1 system is home to at least seven terrestrial planets and is a target of interest for future James Webb Space Telescope (JWST) observations. Although several of these planets are located in the traditional habitable zone, where liquid water could exist on the surface, TRAPPIST-1h is interesting to explore as a potentially habitable ocean world analog. In this study we evaluate the observability of a Titan-like atmosphere on TRAPPIST-1h and what role the upper atmosphere can play in influencing JWST observations. The ability for JWST to detect specific species in the atmosphere at TRAPPIST-1h will depend on how far each species extends from the surface. In order to understand the conditions required for detection, we evaluate the input parameters that are used in one-dimensional models to simulate the structure of a Titan-like atmosphere as a function of altitude. These parameters include the surface temperature and pressure, the temperature profile as a function of distance from the surface, the composition of the minor species relative to N2, and the eddy diffusion coefficient. We find from JWST simulated spectra that observations will be most sensitive to surface temperature, temperature gradients, and surface pressure. The importance of temperature gradients to observations show that a simple isothermal scale height is not the ideal method for evaluating transit spectra from exoplanet atmospheres.