Uranus smells like eggy farts, scientists confirm

Thomas McMullan Read more April 24, 2018

Uranus is home to clouds of hydrogen sulphide and the gas gives the distant planet a distinct “rotten eggs” aroma, a report has confirmed.

Uranus smells like eggy farts, scientists confirm

The composition of Uranus’ atmosphere has been the source of long-running debate, but a team of international scientists now says it has evidence for hydrogen sulphide high in the ice giant’s cloud tops.

The findings were discovered using the Near-Infrared Integral Field Spectrometer (NIFS) instrument on the 8-metre Gemini North telescope, on Hawaii’s Mauna Kea summit, and published in the journal Nature. A team, led by Patrick Irwin from the University of Oxford, used the telescope to spectroscopically dissect the infrared light from the seventh planet in the solar system, pinpointing exactly how its atmosphere absorbs infrared light from the sun.

This “absorption-line data” allows the team to glean the composition of Uranus’ clouds. Scientists have hypothesised for decades about whether these clouds are made from hydrogen sulphide (H₂S) or ammonia (NH₃). “Now, thanks to improved hydrogen sulfide absorption-line data and the wonderful Gemini spectra, we have the fingerprint which caught the culprit,” said Irwin in a statement.

“This work is a strikingly innovative use of an instrument originally designed to study the explosive environments around huge black holes at the centres of distant galaxies,” said Chris Davis, of the US National Science Foundation. “To use NIFS to solve a longstanding mystery in our own solar system is a powerful extension of its use.”

The composition of Uranus’ cloud deck is markedly different to those of the inner gas giants, Jupiter and Saturn. The upper clouds of those planets are instead made up of ammonia ice. Leigh Fletcher, a member of the research team from the University of Leicester in the UK, noted that this difference can likely be traced back to the birth of these distant worlds:

“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 reason why it has taken so long for experts to find evidence for Uranus’ composition has a lot to do with how the planet formed. According to Fletcher, when a cloud deck forms by condensation, it locks the cloud-forming gas in a deep internal reservoir, hidden beneath the levels that astronomer can usually see with telescopes. “Only a tiny amount remains above the clouds as a saturated vapour,” said Fletcher. “And this is why it is so challenging to capture the signatures of ammonia and hydrogen sulfide above cloud decks of Uranus.

“The superior capabilities of Gemini finally gave us that lucky break.”

The discovery helps us understand more about Uranus’ birth and evolution, including the possibility that it migrated from where it originally formed to its current location. It may not smell particularly nice, but it could help unravel the secrets of our solar system’s formation. Besides, even if you were to travel to Uranus, you’d suffocate and freeze to death long before you had a chance to smell anything.