PIE in the Sky: Using Planetary Infrared Excess to Retrieve Exoplanet Atmospheres with JWST

To increase the sample size of future atmospheric characterization efforts, we have built on the planetary infrared excess (PIE) technique that has been proposed as a means to detect and characterize the thermal spectra of transiting and non-transiting exoplanets using sufficiently broad wavelength coverage to uniquely constrain the stellar and planetary spectral components from spatially unresolved observations. We performed simultaneous retrievals of stellar and planetary spectra for the archetypal planet WASP-43b in its original and non-transiting configurations to determine the efficacy of the PIE technique for characterizing the planet’s nightside atmospheric thermal structure and composition using typical out-of-transit JWST observations.

We’ll discuss the results of our retrievals using NIRISS, NIRSpec, and/or MIRI instrument modes and provide expected constraints on WASP-43b’s nightside thermal structure and water abundance. We’ll also demonstrate how to break the degeneracy between planet radius and irradiation temperature for Hot Jupiter exoplanets in non-transiting configurations. If the PIE technique can be shown to be an effective means at studying non-transiting exoplanets, we’ll have opened the door for a large population of exoplanets that will be amenable to atmospheric characterization with JWST and other future mission concepts.

This material is based upon work performed as part of NASA’s CHAMPs team.