Why does Uranus smell of farts?

Credits: Hubble/ NASA/ ESA/ L. Lamy/ Observatoire de Paris

Let the puns start rolling in….. Astronomers have long suspected it, but now they have proof: Uranus stinks. Researchers have in fact announced having detected hydrogen sulphide, the gas that gives rotten eggs – and farts – their distinctive aroma. 

Despite years of observation, the composition of the clouds of Uranus has long remained difficult to discern. After all, more than three billion kilometers separates us from the seventh planet in our solar system. We know however that there is methane in the atmosphere: it is odourless, but gives Uranus its pretty bluish colour. Thanks to the Voyager 2 probe, we also know that there is hydrogen and helium present. But the concentration of other compounds, such as water, ammonia and hydrogen sulphide, is more difficult to determine. Uranus is in fact covered in a cloudy layer, and the gas forming these clouds is hidden underneath – only a small quantity persists above the clouds.

However, observation techniques and equipment are constantly improving. An international team of astronomers recently used the powerful Gemini telescope to scrutinise Uranus. Led by physicist Patrick Irwin from Oxford, the research team used an 8 meter telescope’s Near-Infrared Integral Field Spectrometer (NIFS) to carry out the most detailed ever spectroscopic analysis on Uranus’s clouds.

After having sampled reflected sunlight in an area just above the visible cloud layer, the researchers detected the presence of the famous hydrogen sulphide. In small quantities, certainly, but the gas is well and truly present. The researchers equally distinguished Uranus from the inner gas planets inside our solar system – Jupiter and Saturn – which have plenty of ammonia in their atmospheres, but no hydrogen sulphide above the clouds. Finally, this new work can provide us with  few hints about Neptune, which is similar to Uranus in terms of composition, but which is even further away.

In addition, this new study could teach us more about how our solar system was formed in the first place. “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”, explained scientist Leigh Fletcher of the University of Leicester. This means that the gas giants Jupiter and Saturn were probably formed far away from Uranus and Neptune – and they would all have been formed apart from planets with rocky interiors such as Mercury, Venus, Earth and Mars.

The next generation of terrestrial and space telescopes, such as the Giant Magellan telescope and the James Webb spatial telescope, could be able to obtain a few more details regarding the atmospheric compositions of these planets. However, for a truly detailed analysis, a space probe would need to be sent to study Uranus. This could be the case in 2030, but nothing has yet been confirmed.

You can find all the details of this study in the journal Nature Astronomy.