Unbiasing the density of TTV-characterised sub-Neptunes in multi-planetary systems: re-analysis of 34 Kepler planets

Transit Timing Variations (TTVs) can provide useful information on compact multi-planetary systems observed by transits, by putting constraints on the masses and eccentricities of the observed planets. This is especially helpful when the host star is not bright enough for radial velocity follow-up. However, in the past decades, numerous works have shown that TTV-characterised planets tend to have a lower density than RV-characterised planets. Re-analysing 34 Kepler planets in the super-Earth to sub-Neptunes range using the RIVERS approach, we show that at least part of these discrepancies was due to the way transit timings were extracted from the light curve. We recover robust mass estimations for 23 of the planets and compare them to the RV-characterised population. Our analysis typically shifts the planets from a surprisingly low density in the mass/radius diagram to a new density and composition which is closer to the bulk of known exoplanets. These results are especially important to obtain an unbiased view of the compact multi-planetary systems detected by Kepler, TESS, and the upcoming PLATO mission.