The cloud tops of Uranus smell like rotten eggs, according to a new study of the 7th planet in our Solar System.


This rotten egg smell is a result of the presence of hydrogen sulphide high in Uranus’s cloud deck.

In contrast, the cloud tops of gas giants Jupiter and Saturn feature ammonia, but no hydrogen sulphide.

Hydrogen sulphide is the chemical that gives rotten eggs their smell, and has long thought to be present in Uranus’s upper atmosphere, but this latest study seems to have proven the theory correct.

Scientists came to the conclusion by analysing sunlight reflecting off a region above the visible cloud layer in Uranus’s atmosphere.

The 8-metre Gemini North telescope on Hawaii's Mauna Kea was used to split this light, revealing the presence of the foul-smelling chemical.

The discovery could shed light on the formation and evolution of the planets in our Solar System.

For example, the difference between the clouds on Jupiter and Saturn and those above Uranus could be related to how the Solar System formed.

“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,” says Leigh Fletcher, a member of the team from the University of Leicester.

The content of chemicals in the gases of the planets could also reveal clues about the migration of planets in the early Solar System, as it is thought that the giant planets likely migrated from where they initially formed.

"We've strongly suspected that hydrogen sulphide gas was influencing the millimeter and radio spectrum of Uranus for some time, but we were unable to attribute the absorption needed to identify it positively.


Now, that part of the puzzle is falling into place as well," says Glenn Orton of NASA's Jet Propulsion Laboratory, who was involved in the study.


Iain Todd BBC Sky at Night Magazine
Iain ToddScience journalist

Iain Todd is BBC Sky at Night Magazine's Content Editor. He fell in love with the night sky when he caught his first glimpse of Orion, aged 10.