Hydrogen sulfide, the gas that gives rotten eggs their distinctive odor, permeates the upper atmosphere of the planet Uranus – as has been long debated, but never definitively proven. Scientists discovered evidence of “the noxious gas swirling high in the giant planet’s cloud tops” after observing how sunlight bounced off Uranus’ atmosphere, according to a news release from the Gemini Observatory, a high-power telescope located on top of Hawaii’s Mauna Kea volcano. Hopefully, the proposed spacecraft will be unmanned like its predecessor, Voyager 2, because Orton said the probe will be expected to plunge through Uranus’ pungent clouds. "They found hydrogen sulfide, the odiferous gas that most people avoid, in Uranus's cloud tops," according to a press release from Gemini Observatory, a high-power telescope atop a Hawaiian volcano. Researchers confirmed Monday the seventh planet from the sun has an upper atmosphere full of one of the smelliest chemicals known to humans, hydrogen sulfide, according to a study published by Nature Astronomy. Astronomers have long debated the composition of Uranus’s clouds and whether hydrogen sulfide or ammonia dominate the cloud deck, but lacked definitive evidence either way. Leigh Fletcher, a member of the research team from the University of Leicester in the UK, adds that the differences between the cloud decks of the gas giants (Jupiter and Saturn), and the ice giants (Uranus and Neptune), were likely imprinted way back during the birth of these worlds. Leigh Fletcher, who also worked on the study, said: “During our Solar System’s formation the balance between nitrogen and sulphur (and hence ammonia and Uranus’s newly-detected hydrogen sulfide) was determined by the temperature and location of planet’s formation.”

The researchers also speculated about what the effects of the levels of hydrogen sulphide around Uranus would be on humans. "If an unfortunate human were ever to descend through Uranus's clouds, they would be met with very unpleasant and odiferous conditions," Patrick Irwin, a physicist at the University of Oxford who led the new study, said in the press release. Irwin said atmospheric conditions on Uranus, which include temperatures of negative 200 degrees Celsius and a mixture of hydrogen, helium, and methane, would almost certainly be fatal to humans — long before the bad odor would be a factor.
Scientists using infrared spectroscopy data from the Gemini North telescope have established the presence of hydrogen sulfide in the clouds of Uranus.