Hi All

Mass loss would cause the expansion of the Sun-planet system to conserve angular momentum, but the mass-ratio involved is too low for the expansion to be very much. Contrary to Nick's statement the exosphere of a gas-giant can expand dramatically even at moderate distances from a star, causing bulk loss of mass - but not enough to strip the planet to its core, unlike planets closer in.

There is quite a literature about atmospheric loss that is worth looking at. Search the Astrophysical Database Server here...

ADS

...search for surnames Lammer, Selsis, Guinan over the last ~ 3 years and you will find quite a few papers, some of which are available on-line after a Google search.

Adam