Image: Ryan F Mandelbaum/NASA/Walter Baxter

Scientists have lots of questions about Uranus. Why does Uranus look the way it does, why did Uranus form the way it did, why does Uranus differ so much from other gas giants, like Jupiter and Saturn? But I had a more important question.

What does Uranus smell like?

The question is actually harder to answer than it seems—it’s unlikely we’d ever be able to sniff Uranus. “It’s so cold that there’s not much” in the way of the compounds that we can smell, Jonathan Fortney, director of the Other Worlds Laboratory at the University of California, Santa Cruz, told Gizmodo. “A lot of the things you’d normally think of as volatile gasses,” the smelly ones, “have frozen out of the clouds.”

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Also, if you went to Uranus to try to smell its atmosphere, you’d die. “You wouldn’t want to be in that atmosphere trying to breathe,” Mark Hofstadter, Planetary Scientist at NASA’s Jet Propulsion Laboratory, told Gizmodo. “There’s probably not enough oxygen in these atmospheres to support us.”

We’d have to bring samples of the atmosphere back to Earth, something we’ve only managed to accomplish for a much closer celestial body, the Moon. But if we did bring a little bit of Uranus back home, we’d find a slew of molecules, both smelly and non-smelly, in its toxic air. Mostly, there would be hydrogen, helium and methane from the outermost layers of gas. But deeper inside are traces of other gases, said Hofstadter. There’s hydrogen sulfide, ammonia, methane, and carbon dioxide. There might even be a little bit of phosphine. Deeper down is a metallic sea of liquid ammonia, water and methane, said Fortney. We’ve learned this by observing the planet with spectroscopes, which detect individual wavelengths (colors) of light given off by certain molecules.

“I think the smelliest things are probably... the hydrogen sulfide and the ammonia,” said Hofstadter. The concentrations of those gases are small, less than .8 parts per million of hydrogen sulfide and less than 100 parts per billion for ammonia. However, they can also condense into clouds in the planet’s atmosphere. Stinky clouds.

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Hydrogen sulfide smells like rotten eggs at .01 to 1.5 parts per million, becoming more offensive at 3 to 5 parts per million. Above 30 parts per million, it becomes “sickeningly sweet.”

Hydrogen sulfide gives farts their bad smell.

Then there’s ammonia, whose odor threshold is 5 to 50 parts per million, according to a very silly US Department of Labor Occupational Safety and Health Administration document. Ammonia smells like ammonia—you can easily pick it out of cleaning fluids and cat pee.

And human urine, if it’s too concentrated.

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Other gases might offer scents, but none would improve Ur-stinky-anus’s case. Phosphine is usually odorless, but impurities can make it smell like garlic and decaying fish, according to the Center for Disease Control and Prevention. Should some of the methane, a carbon atom with four hydrogens attached, turn into ethane, which has two carbon atoms, and somehow stick itself to a sulfur atom, you’d end up with ethanethiol. Ethanethiol smells like garlic and skunks, according to the National Center for Biotechnology Information’s PubChem database.

To be fair, the other gas giants probably smell similar, said Fortney. “They’d smell similar but not as strongly. There’s more hydrogen and helium and less of the volatile mixture” in the other gas giants.

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So that’s it, there’s no way around it. Uranus smells like piss and farts.