Abstract
Aims.We study the effect of disequilibrium processes (photochemistry and vertical transport) on mixing ratio profiles of neutral species and on the simulated spectra of a hot Jupiter exoplanet that orbits stars of various spectral types. We additionally address the impact of stellar activity that should be present, to various degrees, in all stars with convective envelopes.Methods.We used the VULCAN chemical kinetic code to compute number densities of species in irradiated planetary atmospheres. The temperature-pressure profile of the atmosphere was computed with the HELIOS code. We also utilized theτ-REx forward model to predict the spectra of planets in primary and secondary eclipses. In order to account for the stellar activity, we made use of the observed solar extreme ultraviolet (XUV) spectrum taken from Virtual Planetary Laboratory as a proxy for an active sun-like star.Results.We find large changes in the mixing ratios of most chemical species in planets orbiting A-type stars, which radiate strong XUV flux thereby inducing a very effective photodissociation. For some species, these changes can propagate very deep into the planetary atmosphere to pressures of around 1 bar. To observe disequilibrium chemistry we favor hot Jupiters with temperaturesTeq= 1000 K and ultra-hot Jupiters, withTeq≈ 3000 K,which also have temperature inversion in their atmospheres. On the other hand, disequilibrium calculations predict no noticeable changes in spectra of planets with intermediate temperatures. We also show that stellar activity similar to that of the modern Sun drives important changes in mixing ratio profiles of atmospheric species. However, these changes take place at very high atmospheric altitudes and thus do not affect predicted spectra. Finally, we estimate that the effect of disequilibrium chemistry in planets orbiting nearby bright stars could be robustly detected and studied with future missions with spectroscopic capabilities in infrared such asJames WebbSpace Telescope and ARIEL.
Highlights
Since the moment of their birth and the accretion of first atmospheres, the evolution of planets is closely related to the evolution of their host stars through a wealth of different processes that are usually summarized under a single definition of the star-planet interaction
Studying the impact of disequilibrium chemistry, we investigate the impact of stellar activity on atmospheres of hot Jupiters (HJs) orbiting young sun-like stars that maintain a high level of XUV radiation during early stages of their evolution
These temperatures correspond to typical conditions found in HJs (Teq 2000 K) and ultra-hot Jupiters (UHJ) (Teq > 2000 K); we note that the classification of UHJ in terms of their temperatures is a matter of debate
Summary
Since the moment of their birth and the accretion of first atmospheres, the evolution of planets is closely related to the evolution of their host stars through a wealth of different processes that are usually summarized under a single definition of the star-planet interaction. Stellar radiation shapes the temperature distribution in planetary atmospheres; stellar activity produces strong nonthermal radiation, such as X-ray and ultraviolet (UV) to extreme ultraviolet (XUV), and energetic particle flux (coronal mass ejections; CME), which all drive atmospheric chemistry out of equilibrium and eventually control processes of atmospheric erosion (Johnstone et al 2019; Dwivedi et al 2019). Among all these processes, stellar radiation is of particular interest because it acts on the atmosphere of every planet and its impact on, for example, atmospheric composition could directly be studied by analyzing the spectra of the planetary atmosphere
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call