TOI-5789.01 planet candidate HARPS-N RVs

It is still unclear, however, what their most likely composition is, that is whether they are predominantly gas dwarfs or water worlds. The sub-Neptunes orbiting bright host stars are very valuable because they are suitable for atmospheric characterization, which can break the well-known degeneracy in planet composition from the planet bulk density, when combined with a precise and accurate mass measurement.

Here we report on the characterization of the sub-Neptune TOI-5789 c, which transits in front of the bright (V=7.3mag and K_s_=5.35mag) and magnetically inactive K1V dwarf HIP 99452 every 12.93 days, thanks to TESS photometry and 141 high-precision radial velocities obtained with the HARPS-N spectrograph. We find that its radius, mass, and bulk density are R_c_=2.86^+0.18^_-0.15_R_{Earth}_, M_c_=5.00+/-0.50M_{Earth}_, and {rho}_c_=1.16+/-0.23gcm^-3^, and we show that TOI-5789c is a promising target for atmospheric characterization with both JWST and, in the future, Ariel.