Allow me to specify (Score 5, Informative)

Ok, it isn't the mass that is surprising, it is the volume. Larger (in mass) exoplanets have been found, sometimes they fall in to the category of Brown Dwarfs. But TrES-4 is hardly massive. According to the article, the density is .2 g/mL and the volume is 1.7 times that of Jupiter. That gives a mass of 1.7*(1.43128*10^15 km^3) * .2 g/mL = 4.866352 * 10^26 kg. Jupiters mass is 1.8986*10^27 kg. That means TrES-4's mass is only about one quarter the mass of Jupiter ((4.866352 * 10^26 kg)/ (1.8986*10^27 kg)= 0.256312651)