Global Chemistry and Thermal Structure Models for the Hot Jupiter WASP-43b and Predictions for JWST

Abstract

The James Webb Space Telescope (JWST) is expected to revolutionize the field of exoplanets. The broad wavelength coverage and the high sensitivity of its instruments will allow characterization of exoplanetary atmospheres with unprecedented precision. Following the Call for the Cycle 1 Early Release Science Program, the Transiting Exoplanet Community was awarded time to observe several targets, including WASP-43b. The atmosphere of this hot Jupiter has been intensively observed but still harbors some mysteries, especially concerning the day-night temperature gradient, the efficiency of the atmospheric circulation, and the presence of nightside clouds. We will constrain these properties by observing a full orbit of the planet and extracting its spectroscopic phase curve in the 5-12 µm range with JWST/MIRI. To prepare for these observations, we performed an extensive modeling work with various codes: radiative transfer, chemical kinetics, cloud microphysics, global circulation models, JWST simulators, and spectral retrieval. Our JWST simulations show that we should achieve a precision of 210 ppm per 0.1 µm spectral bin on average, which will allow us to measure the variations of the spectrum in longitude and measure the night-side emission spectrum for the first time. If the atmosphere of WASP-43b is clear, our observations will permit us to determine if its atmosphere has an equilibrium or disequilibrium chemical composition, providing eventually the first conclusive evidence of chemical quenching in a hot Jupiter atmosphere. If the atmosphere is cloudy, a careful retrieval analysis will allow us to identify the cloud composition.

Equatorial retrograde flow in WASP-43b elicited by deep wind jets?

“…One noteworthy tentative prediction from our simplified WASP-43b simulation is that the night side will emit overall very little flux in the near-to mid-infrared ranges (Figure 7) -even compared to predicted spectra derived from cloudy GCMs that display full superrotation in their simulations (Parmentier et al 2016). This prediction will be testable with observations by JWST/MIRI (Bean et al 2018;Venot et al 2020). There are some shortcomings in these tentative predictions as we will show in the next section.…”

“…WASP-43b appears thus to be a planet that is well suited for comparing different models with each other (see also e.g. Venot et al (2020)). The significance of the lower-boundary treatment has been recently highlighted again for GJ 1214b, a fast rotator (P rot = 1.5 days), where it was found that the dynamics in the deep atmosphere significantly impact the observables in the upper atmosphere (Wang & Wordsworth 2020).…”

“…Such strong horizontal flow convergence will be accompanied by strong vertical mixing of chemical species via the 'chimney'-effect (Zhang & Showman 2018;Parmentier et al 2013). and also Venot et al (2020) investigate the impact of disequilibrium chemistry on WASP-43b but since their simulated 3D atmosphere did not exhibit strong horizontal flow convergence at the morning terminator, the atmospheric flow that they produced, did not show a strong vertical advection chimney. report that zonal quenching is the dominant chemical disequilibrium mechanism, also Venot et al (2020) suggest that the chemical composition is homogenized with longitude (via zonal flow) to that of the dayside.…”

“…Right: Day-side and night-side spectrum of WASP-43b predicted by the 3D climate model of Parmentier et al (2016) with full superrotation (from Venot et al (2020), with permission of V. Parmentier). Their day-side thermal emission is very similar to the emission derived from our model with equatorial retrograde flow for λ = 5 − 12 micron for the cloud-free and MnS cloud case.…”

“…It would be very interesting to use WASP-43b as another benchmark case for dynamics to compare the results of different dynamical solvers, grids and lower boundary prescriptions and to see if and under which they condition they may yield retrograde flow at the equator. Furthermore, Venot et al (2020) showed that WASP-43b is generally an ideal benchmark case also for retrieval models. So far, only HD 209458b was used for such a benchmark exercise (Heng et al 2011) and only for prograde equatorial flow, that is, superrotation.…”