Nonzero eccentricities of warm Neptunes
Close-in planets (with orbital periods less than a few days) undergo strong tidal dissipation that should circularise their orbits in a timescale shorter than the age of the system. However, most Neptune-mass planets in this kind of orbits present nonzero eccentricity, typically around 0.15. In this talk we discuss some mechanisms that can oppose to gravitational tides, namely, thermal atmospheric tides, evaporation of the atmosphere, and excitation from a distant companion. We show the limitations of these different mechanisms and how some of them could, depending on specific properties of the observed planetary systems, account for the nonzero eccentricities presently observed.