Following re-analysis of Hubble Space Telescope observations of primary transits of the extrasolar planet HD 209458b at Lyman \alpha , Ben-Jaffel ( 2007 , BJ007 ) claims that no sign of evaporation is observed .
Here we show that , in fact , this new analysis is consistent with the one of Vidal-Madjar et al .
( 2003 , VM003 ) and supports the detection of evaporation .
The apparent disagreement is mainly due to the disparate wavelength ranges that are used to derive the transit absorption depth .
VM003 derives a ( 15 \pm 4 ) % absorption depth during transit over the core of the stellar Lyman \alpha line ( from -130 km/s to +100 km/s ) , and this result agrees with the ( 8.9 \pm 2.1 ) % absorption depth reported by BJ007 from a slightly expanded dataset but over a larger wavelength range ( \pm 200 km/s ) .
These measurements agree also with the ( 5 \pm 2 ) % absorption reported by Vidal-Madjar et al .
( 2004 ) over the whole Lyman \alpha line from independent , lower-resolution data .
We show that stellar Lyman \alpha variability is unlikely to significantly affect those detections .
The H i atoms must necessarily have velocities above the escape velocities and/or be outside the Roche lobe , given the lobe shape and orientation .
Absorption by H i in HD 209458b ’ s atmosphere has thus been detected with different datasets , and now with independent analyses .
All these results strengthen the concept of evaporating hot-Jupiters , as well as the modelization of this phenomenon .