The orbital distance at which close-in exoplanets maintain their initial mass is investigated by modelling the maximum expected thermal and nonthermal mass loss rates over several Gyr .
Depending on an exosphere formation time and the evolution of the stellar X-ray and EUV flux we expect that thermal evaporation at orbital distances < 0.05 AU may be an efficient loss process for hydrogen-rich exoplanets with masses < 0.25 M _ { Jup } .
Our results indicate that nonthermal mass loss induced by Coronal Mass Ejections of the host star can significantly erode weakly magnetized short periodic gas giants .
The observed exoplanets Gliese 876d at 0.0208 AU with a mass of \sim 0.033 M _ { Jup } and 55 Cnc e at 0.045 AU with a mass of \sim 0.038 M _ { Jup } could be strongly eroded gas giants , while HD69830b , at 0.078 AU , HD160691d at 0.09 AU and HD69830c at 0.18 AU belonged most likely since their origin to the Neptune-mass domain .
The consequences for the planetary population predicted in paper I ( Wuchterl et al .
2006 ) for CoRoTs first field are : ( 1 ) for orbital distances < 0.05 AU ( orbital periods < 4 days ) weakly magnetized or highly irradiated gas giants may loose a large fraction of their initial mass and completely loose their gas envelopes .
( 2 ) Observed planetary mass spectra at these periods that resemble the initial ones would indicate a major effect of magnetic field protection and so far unknown thermospheric cooling processes .
( 3 ) At distances > 0.05 AU the impact of loss processes is minor and the observed mass spectra should be close to the initial ones .