Colonization of Venus
Venus's atmosphere is made mostly out of carbon dioxide, which, after filtering from sulfuric acid, can be used to grow food. Because nitrogen and oxygen are lighter than the carbon-dioxide that makes the atmosphere, breathable-air-filled balloons will float at a height of about . At this height, the temperature is a manageable ; or if we could get higher (see ).
Atmosphere of Uranus
In January 1986, the "Voyager 2" spacecraft flew by Uranus at a minimal distance of 107,100 km providing the first close-up images and spectra of its atmosphere. They generally confirmed that the atmosphere was made of mainly hydrogen and helium with around 2% methane. The atmosphere appeared highly transparent and lacking thick stratospheric and tropospheric hazes. Only a limited number of discrete clouds were observed.