Transit timings variations in the three-planet system: TOI-270

ABSTRACT We present ground- and space-based photometric observations of TOI-270 (L231-32), a system three transiting planets consisting one super-Earth two sub-Neptunes discovered by TESS around bright (K-mag = 8.25) M3V dwarf. The orbit near low-order mean-motion resonances (5:3 2:1) are thus expected to exhibit large transit timing variations (TTVs). Following an extensive observing campaign using eight different observatories between 2018 2020, we now report clear detection TTVs for c d, with amplitudes ∼10 min super-period ∼3 yr, as well significantly refined estimates the radii mean orbital periods all planets. Dynamical modelling alone puts strong constraints on mass ratio d their eccentricities. When incorporating recently published from radial velocity observations, obtain masses $M_{\mathrm{b}}=1.48\pm 0.18\, M_\oplus$, $M_{\mathrm{c}}=6.20\pm 0.31\, $M_{\mathrm{d}}=4.20\pm 0.16\, M_\oplus$ b, c, respectively. also detect small but significant eccentricities : eb 0.0167 ± 0.0084, ec 0.0044 0.0006, ed 0.0066 0.0020. Our findings imply Earth-like rocky composition inner planet, cores additional He/H2O atmosphere outer two. is best constrained systems planets, it remains excellent target atmospheric characterization.