2365178

Target RA (J2000): 137.671341 and deg Target Dec (J2000): -45.09752 and deg Gaia GMag: 10.6 Programme ID: CH_PR230035 PI of observing programme: Merin Title of programme: Dynamical masses and bulk compositions of newly-found TESS and ASTEP-confirmed sub-Neptunes Abstract: The Sub-Neptunes recently detected by the TESS Kepler and K2 surveys continue to challenge our understanding of planetary systems in particular in relationship to the radius valley. Their physical nature also constitutes a mystery with their bulk compositions still allowing them to be either rocky water worlds or gas-giants (e.g. Rogers and Seager 2010) possibly in connection to photoevaporation of their initial atmospheres as they migrate towards the stars (e.g. Owens and Wu 2013) or due to core-powered mass-loss (e.g. Rogers et al. 2021). We request high-quality CHEOPS observations to dynamically determine the planet masses and radii via transit timing variation (TTV) measurements to identify prime targets for atmospheric follow-up characterisation with JWST to put constraints on their formation histories and to search for further non-transiting and still undetected long-period planets via the TTVs. The five planets are the unique best targets for this science case in CHEOPS AO-03 to our knowledge (observable both by CHEOPS and ASTEP not observed by CHEOPS yet and not in the CHEOPS Reserved Target List). [truncated! Please see actual data for full text]