Young sub-Neptunes orbiting TOI-2076 light curves

CHEOPS observations revealed a clear detection for TOI-2076 c at P=21.01538^+0.00084^_-0.00074_d, and allowed us to rule out three of the most likely period aliases for TOI-2076 d. Ground-based photometry further enabled us to rule out remaining aliases and confirm the P=35.12537+/-0.00067d alias. These observations also improved the radius precision of all three sub- Neptunes to 2.518+/-0.036, 3.497+/-0.043, and 3.232+/-0.063 R_{Earth}_.

Our observations also revealed a clear anti-correlated TTV signal between planets b and c likely caused by their proximity to the 2:1 resonance, while planets c and d appear close to a 5:3 period commensurability, although model degeneracy meant we were unable to retrieve robust TTV masses. Their inflated radii, likely due to extended H-He atmospheres, combined with low insolation makes all three planets excellent candidates for future comparative transmission spectroscopy with JWST.