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Professor Patrick Irwin, Physics Fellow at St Anne's, along with other global collaborators has spectroscopically dissected the infrared light from Uranus captured by the eight-meter Gemini North telescope on Hawaii's Maunakea. They found hydrogen sulphide, the odiferous gas that most people avoid, in Uranus’s cloud tops. The long-sought evidence is published in the journal Nature Astronomy.

The Gemini data, obtained with the Near-Infrared Integral Field Spectrometer (NIFS), sampled reflected sunlight from a region immediately above the main visible cloud layer in Uranus's atmosphere. Professor Irwin said: 'While the lines we were trying to detect were just barely there, we were able to detect them unambiguously thanks to the sensitivity of NIFS on Gemini, combined with the exquisite conditions on Maunakea. Although we knew these lines would be at the edge of detection, I decided to have a crack at looking for them in the Gemini data we had acquired.'

Astronomers have long debated the composition of these clouds and these results could help to shed light on how the outer planets formed as differences between Uranus and Jupiter and Saturn are analysed. 

While the results set a lower limit to the amount of hydrogen sulfide around Uranus, it is interesting to speculate what the effects would be on humans even at these concentrations. Professor Irwin said: 'If an unfortunate human were ever to descend through Uranus's clouds, they would be met with very unpleasant and odiferous conditions. However, suffocation and exposure in the -200C atmosphere made of mostly hydrogen, helium and methane would take its toll long before the smell.'

Adapted from the Gemini Observatory Press Release: https://www.gemini.edu/node/21050. 

Photo credit: This image of a crescent Uranus, taken by Voyager 2 on January 24th, 1986, reveals its icy blue atmosphere. Despite Voyager 2’s close flyby, the composition of the atmosphere remained a mystery until now. Image credit: NASA/JPL

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