Vol. 547
In section 10. Planets and planetary systems

Hint of a transiting extended atmosphere on 55 Cancri b

by D. Ehrenreich, V. Bourrier, X. Bonfils, A. Lecavelier des Etangs, et al., A&A 547, A18


55 Cnc is known to host (at least) five planets. 55 Cnc e and 55 Cnc b are the two planets closest to their star. Planet 55 CnC e is a hot super-Earth with a mass of 7.8 Mearth and a semi-major axis of 0.0152 AU. The authors use HST STIS Lyman alpha and Chandra ACIS-S X-ray observations to look for signs of evaporation of these planets. No signal is found for planet 55 CnC e, but the detection of a strong Ly alpha absorption at inferior conjunctions of 55 Cnc b indicates that this planet may be losing mass in a way that is comparable to planets such as HD 209458 b and HD 189733 b, which are in an orbit much closer to their star. This is surprising from a theoretical point of view and calls for additional observations of this intriguing system, and possibly also for new theories for the structure and evolution of exoplanetary exospheres.