No joke: Uranus smells terrible

Uranus smells like rotten eggs, and that is not a joke. A new study finds that the seventh planet from the sun has an upper atmosphere flush with hydrogen sulfide.

Hydrogen sulfide is a gas best known for its repulsive smell; the gas emanates from sewers and volcanoes on Earth, explaining why some hot springs, which are fed by geothermally heated water, smell like breakfast gone bad. Astronomers have now discovered that the gas is common in the cloud tops of Uranus.

That hydrogen sulfide composition is different than what is found in the upper atmospheres of Uranus’ fellow giant planets Jupiter and Saturn, where ammonia dominates, said Leigh Fletcher, a study co-author and senior research fellow in planetary science at the University of Leicester in England. Ammonia is made of nitrogen bonded with hydrogen, while hydrogen sulfide is hydrogen bonded with sulfur.