^ Energy? Hmm. I confess they look more "solid" to me, like crystal. Or maybe changeling material in transition.
I attribute that to the limitations of CGI textures; computer art is better at conveying solid and liquid surfaces than more gaseous or intangible things. "Watery" may have been the closest available skin for what they had in mind, but the surrounding glow and the blue lightning extending around the
Defiant suggest something more energy-based -- at least, by the standards of Trek/sci-fi, where "energy" and gas and plasma and glowy swirly things in general tend to be lumped together. Anyway, one can't take cover details too literally; better to focus on the general impression.