Uranus stinks. No, really, it does

Uranus, as viewed by NASA’s Voyager 2 spacecraft. Image: NASA

In case anyone is wondering, Uranus smells.

Astronomers using the 8-meter Gemini North telescope in Hawaii spectroscopically dissected infrared light reflected from the cloud tops of the seventh planet and detected noxious hydrogen sulphide, a gas familiar to anyone who’s ever encountered rotten eggs.

The composition of Uranus’ atmosphere has long been a bit of a mystery with astronomers debating whether ammonia or hydrogen sulphide dominates. But now, using the Near-Infrared Integral Field Spectrometer with Gemini North, Patrick Irwin from the University of Oxford and a team of collaborators have found definitive traces of the odiferous gas just above the visible cloud tops.

“Thanks to improved hydrogen sulphide absorption-line data and the wonderful Gemini spectra, we have the fingerprint which caught the culprit,” Irwin said in a statement.

While the observation was extremely challenging, “we were able to detect them unambiguously thanks to the sensitivity of NIFS on Gemini, combined with the exquisite conditions on Maunakea,” Irwin said. “Although we knew these lines would be at the edge of detection, I decided to have a crack at looking for them.”

The detection of hydrogen sulphide in the atmosphere of Uranus – and, presumably, Neptune’s – stands in contrast to the atmospheres of the inner gas giants Jupiter and Saturn where ammonia dominates and hydrogen sulphide is absent.

Leigh Fletcher, a collaborator from the University of Leicester, said the differences likely were established during the birth of the solar system due to temperature variations that dictated chemical abundances and the presumed migration of planets from their birthplaces to their current orbits.

The Uranus observations may shed light on the planet’s history and evolution and help refine migration models.

As for how strong the rotten egg smell might be to an astronaut descending on Uranus, Irwin said “they would be met with very unpleasant and odiferous conditions.”

Not to worry, he added. “Suffocation and exposure in the negative 200 degrees Celsius atmosphere made of mostly hydrogen, helium, and methane would take its toll long before the smell.”