Atmospheric characterisation of GJ1214b from transit and eclipse observations

Abstract

The atmospheric characterisation of GJ1214 b has so far remained uncertain due to the observed flatness of the transit spectra of this planet that is typically attributed to the presence of hazes or clouds in its atmosphere. Here we combine for the first time transit and eclipse observations obtained with JWST to benefit from both type of constraints and advance on the atmospheric characterisation of GJ1214 b. Our results reveal that photochemical hazes can be produced at high enough mass fluxes in the atmosphere of GJ1214 b to explain both type of observations. These hazes have a drastic impact on the atmospheric thermal structure, which has further ramifications on the emitted radiation of the planet, as well as, its Bond albedo. Clouds of KCL, NaCL and ZnS composition also form in this atmosphere but their opacity is too small to explain the observed flatness of the transit spectrum. We find that metallicities in the range 2000-3000x solar provide atmospheric structures that are closest to the observations for haze mass fluxes in the range of (1-3)x1E-11 g cm-2 s-1. Correspondingly the Bond albedo is within 10-20%. Moreover, sulfur photochemistry produces abundant OCS that has a detectable signature in the transit spectra and should be seaked for in future observations. Sulfur should also participate to the haze formation in this atmosphere, therefore optical properties of such compounds are needed.