Influence of equilibrium tides on transit-timing variations of close-in super-Earths I. Application to single-planet systems and the case of K2-265 b

With the current growth in the discovery of close-in low-mass exoplanets, recent works have been published with the aim to discuss the influences of planetary interior structure parameters on both the shape of transit light curves as well as variations in the timing of transit events of these planets. One of the main aspects explored in these works is the possibility that the precession of the argument of periapsis caused by planetary tidal interactions may lead to unique effects on the transit light curves of the exoplanets, such as the so-called transit-timing variations (TTVs). In this work, we investigate the influence of planetary tidal interactions on the transit-timing variations of short-period low-mass rocky exoplanets. For this purpose, we employed the recently developed creep tide theory to compute tidally induced TTVs. We implemented the creep tide in the recently-developed Posidonius N-body code, thus allowing for a high-precision evolution of the coupled spin-orbit dynamics of planetary systems. As a working example for the analyses of tidally induced TTVs, we applied our version of the code to the K2-265 b planet. We analyzed the dependence of tidally induced TTVs with the planetary rotation rate, uniform viscosity coefficient, and eccentricity. Our results show that the tidally induced TTVs are more significant in the case where the planet is trapped in nonsynchronous spin-orbit resonances, in particular the 3/2 and 2/1 spin-orbit resonant states. An analysis of the TTVs induced separately by apsidal precession and tidally induced orbital decay has allowed for the conclusion that the latter effect is much more efficient at causing high-amplitude TTVs than the former effect by 2-3 orders of magnitude. We compare our findings for the tidally induced TTVs obtained with Posidonius with analytical formulations for the transit timings used in previous works, and we verified that the results for the TTVs coming from Posidonius are in excellent agreement with the analytical formulations. These results show that the new version of Posidonius containing the creep tide theory implementation can be used to study more complex cases in the future. For instance, the code can be used to study multiplanetary systems, in which case planet-planet gravitational perturbations must be taken into account in addition to tidal interactions to obtain the TTVs.