Converting the sub-Jovian desert of exoplanets to a savanna with TESS, PLATO, and Ariel

Abstract

ABSTRACT There is a lack of exoplanets with sizes similar to Neptune orbiting their host stars with periods ≲3 d – hence the name ‘sub-Jovian/Neptune desert’. Recently, several exoplanets have been confirmed to reside in the desert, transforming it into a ‘savanna’ with several ‘giraffe’ planets (such as LTT 9779 b and TOI-674 b). The most prominent scenarios put forward for the explanation of the formation of the desert are related to the stellar irradiation destroying the primary atmosphere of certain specific exoplanets. We aim to present three targets (LTT 9779 b, TOI-674 b, and WASP-156 b) that, when observed at wide wavelength ranges in infrared (IR), could prove the presence of these processes, and therefore improve the theories of planetary formation/evolution. We simulate and analyse realistic light curves of the selected exoplanets with PLATO/N-CAM and the three narrow-band filters of Ariel (VISPhot, FGS1, and FGS2) based on TESS observations of these targets. We improved the precision of the transit parameters of the three considered planets from the TESS data. We find that the combination of the three narrow-band filters of Ariel can yield an inner precision of ${\lesssim}1.1\ \hbox{per cent}$ for the planetary radii. Data from the three telescopes together will span decades, allowing the monitoring of changes in the planetary atmosphere through radius measurements. The three selected ‘giraffe’ planets can be golden targets for Ariel, whereby the loss of planetary mass due to stellar irradiation could be studied with high precision, multiwavelength (spectro-)photometry.