On the Survival of Short-Period Terrestrial Planets

The currently feasible method of detection of Earth-mass planets is transit photometry, with detection probability decreasing with a planet's distance from the star. The existence or otherwise of short-period terrestrial planets will tell us much about the planet formation process, and such planets are likely to be detected first if they exist. Tidal forces are intense for short-period planets, and result in decay of the orbit on a timescale which depends on properties of the star as long as the orbit is circular. However, if an eccentric companion planet exists, orbital eccentricity ($e_i$) is induced and the decay timescale depends on properties of the short-period planet, reducing by a factor of order $10^5 e_i^2$ if it is terrestrial. Here we examine the influence companion planets have on the tidal and dynamical evolution of short-period planets with terrestrial structure, and show that the relativistic potential of the star is fundamental to their survival.