Orbital effects of non-isotropic mass depletion of the atmospheres of evaporating hot Jupiters in extrasolar systems

Abstract

We analytically and numerically investigate the long-term, i.e. averaged over one full revolution, orbital effects of the non-isotropic percent mass loss \dot m/m experienced by several transiting hot Jupiters whose atmospheres are hit by severe radiations flows coming from their close parent stars. The semi-major axis a, the argument of pericenter \omega and the mean anomaly M experience net variations, while the eccentricity e, the inclination I and the longitude of the ascending node remain unchanged, on average. In particular, a increases independently of e and of the speed Vesc of the ejected mass. By assuming |\dot m| <= 10^17 kg yr-1, corresponding to |\dot m/m| <= 10^-10 yr-1 for a Jupiter-like planet, it turns out \dot a = 2.5 m yr^-1 for orbits with a = 0.05 au. Such an effect may play a role in the dynamical history of the hot Jupiters, especially in connection with the still unresolved issue of the arrest of the planetary inward migrations after a distance a >= 0.01 au is reached. The retrograde pericenter variation depends, instead, on e and V_esc. It may, in principle, act as a source of systematic uncertainty in some proposed measurements of the general relativistic pericenter precession; however, it turns out to be smaller than it by several orders of magnitude.