Atmosphere of Uranus at the solstice of 1986, when "Voyager 2" passed by the planet, they were concentrated near the sunlit pole, making it dark in ultraviolet light. The outermost layer of the Uranian atmosphere, extending for thousands of kilometres, is the thermosphere/exosphere, which has a uniform temperature of around 800 to 850 K. This is much higher than, for instance, the 420 K observed in the thermosphere of Saturn. The heat sources necessary to sustain such high temperatures are not understood, since neither solar FUV/EUV radiation nor auroral activity can provide the necessary energy. The weak cooling efficiency due to the depletion
Far-infrared astronomy Earth's atmosphere is opaque over most of the far-infrared, so that ground-based observations are limited to submillimetre wavelengths using high-altitude telescopes such as the James Clerk Maxwell Telescope, the Caltech Submillimeter Observatory, the High Elevation Antarctic Terahertz Telescope and the Submillimeter Array. Most far-infrared astronomy is performed by satellites such as the Herschel Space Observatory, Spitzer Space Telescope, IRAS, and Infrared Space Observatory. Upper-atmosphere observations are also possible, as conducted by the airborne SOFIA telescope. On 22 January 2014, European Space Agency scientists reported the detection, for the first definitive time, of water vapor on the dwarf planet, Ceres, largest