Two pictures of Uranus.
Image: ESA/Hubble (Wikimedia Commons)

I’m sick and tired of Uranus jokes. It’s time to get serious about Uranus, because there is some really serious science surrounding Uranus’s mysteries. And wow, is Uranus mysterious.

Following some of our very serious informed speculation, scientists have directly observed a molecule in the planet’s deep atmosphere that confirms Uranus’s stench. That molecule is hydrogen sulfide, and it’s important for more reasons than just determining the planet’s scent.

“It adds another piece of information about the planets and how they form,” study author Patrick Irwin from the University of Oxford told Gizmodo. “Uranus and Neptune formed in a colder part of the solar nebula,” the early stage of our solar system when it was just our young sun and lots of dust, “than Jupiter and Saturn.”

Scientists have long assumed that cloud tops near the giant green planet’s surface contained hydrogen sulfide and ammonia, but that hypothesis has been based on inference rather than direct observations. Scientists figured these molecules were there based on an unexplained absence of certain wavelengths of light. It’s like guessing something’s identity based on a warped version of the shadow it casts without really looking at it.

The team peered deep into Uranus’s atmosphere, at and below the part we might call its “surface,” using the Gemini-North’s Near-infrared Integral Field Spectrometer in Hawaii. They report that they’ve directly detected the molecule at around 0.4-0.8 parts per million as ice in its cloud tops. They measured more hydrogen sulfide than ammonia, and also the exact concentration of hydrogen sulfide required to produce a rotten-egg fart smell. They published their paper today in Nature Astronomy.

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Irwin confirmed that visiting astronauts would notice the stench as they descended into the planet’s atmosphere. Things would get more dangerous once they got below the hydrogen sulfide cloud deck, where they’d experience the coldest atmosphere in the solar system and probably die.

This observation is actually important for understanding the composition of the dust disk that formed the Sun, as well as why Jupiter and Saturn formed into gas giants but Uranus and Neptune remained slightly smaller ice giants. The researchers found less ammonia than expected, probably due to where Uranus formed in the disk of dust—someplace with just the right temperature and composition to make a planet like Uranus, explained Imke de Pater from the University of California, Berkeley in a commentary.

Perhaps one day human astronauts will be lucky enough to sniff Uranus directly!

[Nature Astronomy]

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