  We analyze the long-term tidal evolution of a single-planet system through
the use of numerical simulations and averaged equations giving the variations
of semi-major axis and eccentricity of the relative orbit. For different types
of planets, we compute the variations due to the planetary and stellar tides.
Then, we calculate the critical value of the eccentricity for which the stellar
tide becomes dominant over the planetary tide. The timescales for orbital decay
and circularization are also discussed and compared.
