Here's a question for the professionals out there. I'm relatively well-educated with regard to planetary science and basic physics (from an advanced amateur's perspective, anyway), and I've always been bothered by the oft-repeated statement that the gas giant planets lack any definite solid (or liquid) surface. It seems to me that there should at the very least be a zone of phase change, where the gaseous atmosphere changes phase to either solid or liquid (rain/snow equivalent?), and while this may occur at a depth and pressure such that the gas phase has a really high viscosity, I would find it difficult not to interpret this interface as a surface which could be a target by a really robust lander. Am I missing something with regard to the physics here? For example I could envision the phase transition being glass-like, so that the viscosity just smoothly transitions between one phase and the other, without a discontinuity, yet at least in the case of H20, I know that this isn't the case. So what is really going on here? It almost seems like this region is so far beyond the realm of familiar physics that the typical scientist gives up in despair and provides a simplistic non-answer. Clearly Uranus or Neptune would have the most easily accessible surfaces - and according to planetary models similar to those shown on this page:
it looks like those surfaces will be water overlain by H2 gas. Looks like one heck of a planetery ocean, assuming that the water isn't hot ice at these pressures.