Are the planets discovered around other stars gas giants like Jupiter, or are the big balls of rock?

Calculations seem to suggest that a gaseous planet like a 'Jupiter' can exist at amazingly close distances to its star, at least to the orbit of Mercury. The gravity fields of these giant planets are so strong that they can restrain much of the evaporation of their atmospheres by the shear force of their gravity. The outer layers of their atmospheres would have to be at temperatures in excess of 1000 Kelvins.

I know of no physical reason why the planets cannot be massive, airless, rocky bodies several times the mass of Jupiter. Until detailed spectroscopic studies can be performed, we will not know what their atmospheres and compositions may be like. Right now, only poorly validated theoretical models provide any guidance, and they have only been validated in ONE planetary system...ours!