Planet Uranus smells like rotten eggs

The planet Uranus has clouds made up of hydrogen sulphide, the gas that gives rotten eggs their unpleasant smell, a study has found. This discovery is significant as it may help scientists and astronomers understand how the early solar system was formed and how it evolved over time, researchers said.

Based on sensitive spectroscopic observations with the Gemini North telescope, scientists, including those from the University of Leicester in the UK, have uncovered the noxious gas swirling high above the giant planet's cloud tops. This result, published in the journal Nature Astronomy, resolves a stubborn, long-standing mystery of one of our neighbours in space, researchers said. Even after decades of observations, and a visit by the Voyager 2 spacecraft, Uranus has held on to one critical secret - the composition of its clouds.

Patrick Irwin from the University of Oxford, UK and colleagues spectroscopically dissected the infrared light from Uranus captured by the 8-metre Gemini North telescope on Hawaii’s Maunakea. They found hydrogen sulphide, the odiferous gas that most people avoid, in Uranus’s cloud tops.

Scientists have long debated the composition of Uranus’s clouds and whether hydrogen sulphide or ammonia dominate the cloud deck, but have lacked definitive evidence either way. “Now, thanks to improved hydrogen sulphide absorptionline data and the wonderful Gemini spectra, we have the fingerprint which caught the culprit,” said Leigh Fletcher from the University of Leicester.

The spectroscopic absorption lines (where the gas absorbs some of the infrared light from reflected sunlight) are especially weak and challenging to detect, according to Irwin.