Evidence of energy-, recombination-, and photon-limited escape regimes in giant planet H/He atmospheres
M. Lampón, M. López-Puertas, S. Czesla, A. Sánchez-López, L. M. Lara, M. Salz, J. Sanz-Forcada, K. Molaverdikhani, A. Quirrenbach, E. Pallé, J. A. Caballero, Th. Henning, L. Nortmann, P. J. Amado, D. Montes, A. Reiners, I. Ribas
Abstract
Hydrodynamic escape is the most efficient atmospheric mechanism of planetary mass loss and has a large impact on planetary evolution. Three hydrodynamic escape regimes have been identified theoretically: energy-limited, recombination-limited, and photon-limited. However, no evidence of these regimes had been reported until now. Here, we report evidence of these three regimes via an analysis of a helium I triplet at 10 830 Å and Ly α absorption involving a 1D hydrodynamic model that allows us to estimate hydrogen recombination and advection rates. In particular, we show that HD 209458 b is in the energy-limited regime, HD 189733 b is in the recombination-limited regime, and GJ 3470 b is in the photon-limited regime. These exoplanets can be considered as benchmark cases for their respective regimes.