Uranus in the upper clouds consists of the same molecules that give rotten eggs their toxic odor, according to a new study. Using a spectrograph at the Gemini North Telescope in Hawaii, Fletcher and his colleagues tracked the chemical composition of the gas in Uranus upper clouds. This is not entirely surprising: observations in the 1990s showed the presence of ammonia, a gas with a similar smell to rotten eggs. However, this gas has not yet been unambiguously detected, according to the study authors. The hydrogen sulfide clouds on Uranus set it apart from the gas giants Jupiter and Saturn, whose skyscrapers are largely made of ammonia. These clouds are not only smelly but can also help capture details about the early solar system.