Uranus isn’t the most popular place in the Solar System. It’s a cold, harsh world, and it hasn’t been studied nearly as much as some of our other planetary neighbors like Jupiter, Saturn, and of course Mars. In fact, despite many years of observations, scientists long wondered exactly what its frosty atmosphere is composed of. Thanks to a new research effort led by Patrick Irwin of the University of Oxford, we now have a pretty good idea of what Uranus actually smells like, and it isn’t pleasant.

By studying the planet’s clouds with a spectrometer, the research team was able to determine that the atmosphere contains hydrogen sulfide, which happens to be the putrid gas that rotten eggs give off. Uranus is one seriously smelly place.

The research, which was published in Nature Astronomy, focused on the reflection of sunlight after it bounced off of the clouds of Uranus. By measuring the wavelengths of the light that were reflected, the team could determine that the noxious gas was abundant. The team used the Gemini North telescope, located in Hawaii, to make the observations, and noted that such a discovery was only possible thanks to more advanced data related to the gas’s absorption of infrared light.

“The detection of hydrogen sulfide high in Uranus’s cloud deck (and presumably Neptune’s) contrasts sharply with the inner gas giant planets, Jupiter and Saturn, where no hydrogen sulfide is seen above the clouds, but instead ammonia is observed,” the researchers explain in a statement announcing the discovery. “The bulk of Jupiter and Saturn’s upper clouds are comprised of ammonia ice, but it seems this is not the case for Uranus. These differences in atmospheric composition shed light on questions about the planets’ formation and history.”

As for what might happen if a human were to attempt to endure the foul clouds of Uranus, it’s not a pretty picture. “If an unfortunate human were ever to descend through Uranus’s clouds, they would be met with very unpleasant and odiferous conditions,” Irwin explains. “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.”

Note to self: Steer clear of Uranus.