It's a punchline that sends every 12-year-old boy into a fit of giggles. Now it has been proven to be true. Uranus stinks!

Scientists using a huge telescope on Hawaii's Mauna Kea volcano found the seventh planet from the sun is surrounded by clouds made up of hydrogen sulfide, the gas that smells like rotten eggs and bad flatulence.

The study by scientists from the California Institute of Technology, University of Oxford and the University of Leicester was published in the journal Nature Astronomy.

"If an unfortunate human were ever to descend through Uranus' clouds they would be met with very unpleasant and odiferous conditions," Patrick Irwin of the University of Oxford wrote.

Not that they would live long enough to sniff it. "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," Irwin wrote.

Despite previous observations by ground telescopes and the Voyager 2 spacecraft, scientists had failed to determine the composition of Uranus' atmosphere.

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The new data was obtained by using a spectrometer on the Gemini North telescope in Hawaii. It should help scientists better understand the formation of Uranus and other outer planets. VOA