Free access article

A&A 418, L1-L4 (2004)
DOI: 10.1051/0004-6361:20040106

Letter

Atmospheric escape from hot Jupiters

A. Lecavelier des Etangs¹, A. Vidal-Madjar¹, J. C. McConnell² and G. Hébrard<sup>1

1</sup>  Institut d'Astrophysique de Paris, CNRS, 98bis boulevard Arago, 75014 Paris, France
²  Department of Earth and Atmospheric Science, York University, North York, Ontario, Canada

(Received 10 November 2003 / Accepted 4 March 2004)

Abstract
The extra-solar planet HD 209458b has been found to have an extended atmosphere of escaping atomic hydrogen (Vidal-Madjar et al. 2003), suggesting that "hot Jupiters" closer to their parent stars could evaporate. Here we estimate the atmospheric escape (so called evaporation rate) from hot Jupiters and their corresponding life time against evaporation.

The calculated evaporation rate of HD 209458b is in excellent agreement with the H I Lyman- observations.

We find that the tidal forces and high temperatures in the upper atmosphere must be taken into account to obtain reliable estimate of the atmospheric escape. Because of the tidal forces, we show that there is a new escape mechanism at intermediate temperatures at which the exobase reaches the Roche lobe. From an energy balance, we can estimate plausible values for the planetary exospheric temperatures, and thus obtain typical life times of planets as a function of their mass and orbital distance.

Key words: star: individual: HD 209458 -- stars: planetary systems

Offprint request: A. Lecavelier des Etangs, lecaveli@iap.fr

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