A design similar to Fuller's "Cloud Nine" might permit habitation in the upper atmosphere of Venus, where at ground level the temperature is too high and the atmospheric pressure too great. As proposed by Geoffrey A. Landis, the easiest planet (other than Earth) to place floating cities at this point would appear to be Venus. Because the thick carbon dioxide atmosphere is 50% denser than air, breathable air (21:79 Oxygen-Nitrogen mixture) is a lifting gas in the dense Venerean atmosphere, with over 60% of the lifting power that helium has on Earth. In effect, a balloon full of human-breathable air would sustain itself and extra weight (such as a habita) in midair. This means that any large structure filled with air would float on the carbon dioxide, with the air's natural buoyancy counteracting the weight of the structure itself.