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Target RA (J2000): 145.827866 and deg Target Dec (J2000): 15.00436 and deg Gaia GMag: 10.5 Programme ID: CH_PR140068 Programme Manager: EGGER PI of observing programme: Benz Title of programme: Axis 1 - Constraining the abundance of water in hot planets (HotWatermelon) Abstract: Planets located close enough to their star experience evaporation which leads to a dichotomy in the possible gas content of these objects. These planets either contain more than around one percent of gas (in mass) or no gas at all (see Owen and Wu 2017). This dichotomy when expressed in term of mass-radius relation implies the existence of a region in the mass-radius diagram of hot planets where dry planets cannot exist. We propose to observe planets that could lie in this region with CHEOPS. Combining a precise radius and mass will allow us to identify planets in this forbidden region hence showing that they have to contain volatiles most likely water. Our data combined with future JWST observations will also constrain the efficiency of evaporation. [truncated! Please see actual data for full text]