Uranus Stinks

Uranus

No Joke: Uranus Smells Terrible, Study Says

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.
. . .
"If an unfortunate human were to ever descend through Uranus' clouds, they would be met with very unpleasant and odiferous conditions," study co-author Patrick Irwin, a professor of planetary physics at the University of Oxford, said in the statement. That is, they would if that person miraculously lived to take a whiff.

"Suffocation and exposure in the negative 200 degrees Celsius [minus 328 degrees Fahrenheit] atmosphere made of mostly hydrogen, helium and methane would take its toll long before the smell," Irwin added.

On the other hand, hydrogen sulfide is remarkably toxic, more toxic than hydrogen cyanide and for a similar reason, it binds cytochromes, and blocks cellular respiration. The only reason that isn't terribly well known is that the smell is so powerful and obnoxious it usually drives people away before they get a significant dose. However, the nose gets saturated by the odor, and that sometimes allows people to get poisoned.

Hydrogen sulfide is also the smell of "black mud", the result of the anaerobic decomposition of organic matter in the presence of sulfate, in a process called sulfate reduction, by sulfate reducing bacteria.

Georgia helped study the role sulfate reducing bacteria in the methylation of mercury. It turns out that many, but not all sulfate reducing bacteria can produce methyl mercury, the toxic form that accumulates in fish, and most of the methyl mercury in the environment is produced by them. Consequently, she and the lab she worked for, spent a lot of time visiting, sampling and measuring muddy environments with that nasty rotten egg odor. We jokingly called it the smell of money.