Planetary radius as a function of the stellar irradiation received by the planet (based on Fulton et al. 2017). TOI-402.01 stands just below the radius gap while TOI-402.02 stands above. The GJ 9827 system is added here as it represents, with TOI-402, probably the best system to understand the radius gap through exoplanetology comparison. HD 97658b is also added for a direct comparison with TOI-402.02 as they are supposed to have water-rich composition and, furthermore, a search for photo-dissociation of water has been undertaken on HD 97658b by Bourrier et al. (2017). The data at the origin of this diagram have been extracted from the NASA exoplanet archive (https://exoplanetarchive.ipac.caltech.edu).