Image copyright NASA Image caption The discovery confirms a long-held idea about Uranus' atmosphere 
 
 The planet Uranus has clouds made up of hydrogen sulphide, the gas that gives rotten eggs their unpleasant smell. 
 
 The possibility of this gas being present in the atmosphere of the seventh planet had long been debated, but has now been confirmed for the first time by observations at a telescope on Hawaii. 
 
 The malodorous gas was detected high above the giant planet's cloud tops. 
 
 The findings could shed important new light on how the outer planets formed. 
 
 A team of researchers have published their results in the journal Nature Astronomy. 
 
 Despite previous observations by ground telescopes and the Voyager 2 spacecraft, the composition of Uranus' atmosphere had remained unclear. 
 
 Scientists have long wondered whether hydrogen sulphide (H₂S) or ammonia (NH₃) dominate the ice giant's cloud deck, but have lacked definitive evidence either way. 
 
 The data were obtained with the Near-Infrared Integral Field Spectrometer (NIFS) instrument on the Gemini North telescope on Hawaii's Mauna Kea summit. 
 
 The spectroscopic measurements break infrared light from Uranus into its component wavelengths. Bands in the resulting spectrum known as absorption lines, where the gas absorbs infrared light coming from the Sun, allowed the scientists to "fingerprint" components of Uranus' atmosphere. 
 
 "Now, thanks to improved hydrogen sulphide absorption-line data and the wonderful Gemini spectra, we have the fingerprint which caught the culprit," said co-author Patrick Irwin, from the University of Oxford. 
 
 Image copyright SPL Image caption The detection was made using observations from the Gemini North observatory on Maunakea, Hawaii 
 
 The detection of hydrogen sulphide high in Uranus' cloud deck, sets up a contrast with inner gas giant planets such as Jupiter and Saturn. The bulk of Jupiter and Saturn's upper clouds are instead comprised of ammonia ice. 
 
 The researchers say these differences in atmospheric composition shed light on questions about the planets' formation and history. 
 
 Co-author Dr Leigh Fletcher, from the University of Leicester, said that these differences were probably imprinted early on in the history of these worlds. 
 
 He explained that the balance between different gases in the atmospheres of these planets was probably determined by the conditions where they formed in the early Solar System. 
 
 According to Dr Fletcher, when a cloud deck forms by condensation, it locks away the cloud-forming gas in a deep internal reservoir, hidden away beneath the levels that we can usually see with our telescopes. 
 
 "Only a tiny amount remains above the clouds as a saturated vapour... and this is why it is so challenging to capture the signatures of ammonia and hydrogen sulphide above cloud decks of Uranus," he said. 
 
 "The superior capabilities of Gemini finally gave us that lucky break." 
 
 Glenn Orton, of Nasa's Jet Propulsion Laboratory (JPL) in Pasadena, who worked on the study, said: "We've strongly suspected that hydrogen sulphide gas was influencing the millimetre spectrum of Uranus for some time, but we were unable to attribute the absorption needed to it uniquely. Now, that part of the puzzle is falling into place as well." 
 
 Dr Irwin explained: "If an unfortunate human were ever to descend through Uranus's clouds, they would be met with very unpleasant and odiferous conditions." 
 
 But he added: "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." 

 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. 
 
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 “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] 
 
 

 [/caption] 
 
 Go ahead and say Uranus. Feel free to giggle if you like. I know, I know, it sounds like a dirty word. So what is the proper pronunciation of Uranus. Is there a way to talk about it without having school kids giggle. 
 
 The standard way to pronounce Uranus among astronomers is to put the emphasis on the first syllable “ur” and then say the second part “unus”. This is the standard literary pronunciation. The more common way people have pronounced it is u-ra-nus, with the “ra” sounded like “ray”. 
 
 The truth is that all the different ways of pronouncing Uranus are perfectly fine, even the way that sounds a little dirty. 
 
 We have written many articles about Uranus here on Universe Today. Here’s an article about the rings of Uranus seen edge on. And here’s one about a dark spot in its clouds. 
 
 If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus. 
 
 We have recorded an episode of Astronomy Cast just about Uranus (we even talk about how to pronounce it). You can access it here: Episode 62: Uranus. 
 
 By Fraser Cain - 
 
 Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay. 

 Hydrogen sulfide, the gas that gives rotten eggs their distinctive odor, permeates the upper atmosphere of the planet Uranus - as has been long debated, but never definitively proven. Based on sensitive spectroscopic observations with the Gemini North telescope, astronomers uncovered the noxious gas swirling high in the giant planet's cloud tops. This result resolves a stubborn, long-standing mystery of one of our neighbors in space. 
 
 Even after decades of observations, and a visit by the Voyager 2 spacecraft, Uranus held on to one critical secret, the composition of its clouds. Now, one of the key components of the planet's clouds has finally been verified. 
 
 Patrick Irwin from the University of Oxford, UK and global collaborators spectroscopically dissected the infrared light from Uranus captured by the 8-meter Gemini North telescope on Hawaii's Maunakea. They found hydrogen sulfide, the odiferous gas that most people avoid, in Uranus's cloud tops. The long-sought evidence is published in the April 23rd issue of the journal Nature Astronomy. 
 
 The Gemini data, obtained with the Near-Infrared Integral Field Spectrometer (NIFS), sampled reflected sunlight from a region immediately above the main visible cloud layer in Uranus's atmosphere. "While the lines we were trying to detect were just barely there, we were able to detect them unambiguously thanks to the sensitivity of NIFS on Gemini, combined with the exquisite conditions on Maunakea," said Irwin. "Although we knew these lines would be at the edge of detection, I decided to have a crack at looking for them in the Gemini data we had acquired." 
 
 "This work is a strikingly innovative use of an instrument originally designed to study the explosive environments around huge black holes at the centers of distant galaxies," said Chris Davis of the United State's National Science Foundation, a leading funder of the Gemini telescope. "To use NIFS to solve a longstanding mystery in our own Solar System is a powerful extension of its use." Davis adds. 
 
 Astronomers have long debated the composition of Uranus's clouds and whether hydrogen sulfide or ammonia dominate the cloud deck, but lacked definitive evidence either way. "Now, thanks to improved hydrogen sulfide absorption-line data and the wonderful Gemini spectra, we have the fingerprint which caught the culprit," says Irwin. 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. 
 
 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 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. 
 
 Leigh Fletcher, a member of the research team from the University of Leicester in the UK, adds that the differences between the cloud decks of the gas giants (Jupiter and Saturn), and the ice giants (Uranus and Neptune), were likely imprinted way back during the birth of these worlds. "During our Solar System's formation the balance between nitrogen and sulphur (and hence ammonia and Uranus's newly-detected hydrogen sulfide) was determined by the temperature and location of planet's formation." 
 
 Another factor in the early formation of Uranus is the strong evidence that our Solar System's giant planets likely migrated from where they initially formed. Therefore, confirming this composition information is invaluable in understanding Uranus' birthplace, evolution and refining models of planetary migrations. 
 
 According to Fletcher, when a cloud deck forms by condensation, it locks away the cloud-forming gas in a deep internal reservoir, hidden away beneath the levels that we can usually see with our telescopes. "Only a tiny amount remains above the clouds as a saturated vapour," said Fletcher. "And this is why it is so challenging to capture the signatures of ammonia and hydrogen sulfide above cloud decks of Uranus. The superior capabilities of Gemini finally gave us that lucky break," concludes Fletcher. 
 
 Glenn Orton, of NASA's Jet Propulsion Laboratory, and another member of the research team notes, "We've strongly suspected that hydrogen sulfide gas was influencing the millimeter and radio spectrum of Uranus for some time, but we were unable to attribute the absorption needed to identify it positively. Now, that part of the puzzle is falling into place as well." 
 
 While the results set a lower limit to the amount of hydrogen sulfide around Uranus, it is interesting to speculate what the effects would be on humans even at these concentrations. "If an unfortunate human were ever to descend through Uranus's clouds, they would be met with very unpleasant and odiferous conditions." But the foul stench wouldn't be the worst of it according to Irwin. "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," concludes Irwin. 
 
 The new findings indicate that although the atmosphere might be unpleasant for humans, this far-flung world is fertile ground for probing the early history of our Solar System and perhaps understanding the physical conditions on other large, icy worlds orbiting the stars beyond our Sun. 
 
 ### 

 A photo of Uranus taken by Voyager 2 in 1986 (edited to show its moon and rings). NASA/JPL-Caltech 
 
 Uranus, the seventh planet from the sun, has held a vital (and smelly) secret of the solar system for decades. 
 
 An international team of researchers reported on Monday that they've discovered evidence that Uranus holds one of the most unpleasant-smelling chemicals known to humankind. 
 
 "They found hydrogen sulfide, the odiferous gas that most people avoid, in Uranus's cloud tops," according to a press release from Gemini Observatory, a high-power telescope atop a Hawaiian volcano. 
 
 Voyager 2 was the only spacecraft ever to visit the chilly, blue-green "ice giant." The probe tried to see which chemicals were in Uranus' clouds during its 1986 flyby, but it couldn't tell scientists for certain. 
 
 Now, however, astronomers have used an instrument at the Gemini Observatory to "sniff" the planet's gases from Earth. Their discovery could help write the book on when and where the planets of the solar system formed — and if they ever switched places. 
 
 "This is evidence of a big shakeup early on in the solar system's formation," Glenn Orton, a co-author of the new study and a planetary scientist at NASA's Jet Propulsion Laboratory, told Business Insider. "There was definitely a migration taking place." 
 
 The journal Nature Astronomy published the findings on Monday. 
 
 Why it took so long to detect Uranus's stinky clouds 
 
 The Gemini North telescope at Mauna Kea, Hawaii, which is part of the Gemini Observatory project. Dave Mosher The reason most people avoid hydrogen sulfide is because the compound is a signature ingredient in the scent of rotten eggs — and farts. 
 
 Humans can smell hydrogen sulfide when it makes up as little as three out of every billion molecules in the air, the EPA says. At higher concentrations, such as near volcanic areas, it can be poisonous. Breathing a concentration of a few hundred parts per million can kill a person in about half an hour, according to the Centers for Disease Control. 
 
 "If an unfortunate human were ever to descend through Uranus's clouds, they would be met with very unpleasant and odiferous conditions," Patrick Irwin, a physicist at the University of Oxford who led the new study, said in the press release. But he added that "suffocation and exposure" to Uranus' -200 degree Celsius temperatures "would take its toll long before the smell." 
 
 Researchers had long suspected that Uranus's atmosphere was laced with hydrogen sulfide, and in concentrations dozens of times higher than at Saturn or Jupiter. 
 
 They couldn't be certain, though, since Uranus orbits the sun from 1.85 billion miles away. 
 
 The vast distance, aside from making the planet distant and difficult to study, leads to blisteringly cold temperatures that freezes hydrogen sulfide. Hydrogen-sulfide ice can form clouds, but the solid crystals are hard for chemical-analyzing instruments called spectrometers to study. (The method works far better with liquids and gases.) 
 
 Irwin and others suspected there were at least whiffs of hydrogen sulfide gas drifting above the clouds. And now, thanks to an extremely sensitive Gemini instrument that can see light invisible to humans, Irwin said scientists "have the fingerprint which caught the culprit." 
 
 Why the discovery might 'shake up' ideas about the solar system's evolution 
 
 An artist's conception of the dust and gas surrounding a newly formed planetary system. NASA 
 
 Astronomers like Irwin have an interest in hydrogen sulfide on Uranus that goes far beyond the gas' smell. 
 
 The discovery of hydrogen sulfide may help piece together the story of how the solar system formed and arranged itself some 4.6 billion years ago. Figuring out the exact makeup of distant planets could help determine where in the solar system they first formed — and how far they migrated away from the sun afterward. 
 
 Like all planets, Uranus and Neptune formed from a giant disk of gas and dust that shrouded the sun some 4.6 billion years ago. The planets are mostly made of heavier elements, and didn't balloon with lightweight hydrogen and helium gases. 
 
 "Uranus and Neptune never had the time to grow into gas giants like Jupiter and Saturn," Imke de Pater, an astronomer at the University of California Berkeley who wasn't involved in the study, wrote in an accompanying article in Nature Astronomy. "The composition of a celestial body is a fundamental parameter in determining its formation and evolutionary history." 
 
 The two planets failed to become gas giants (and instead became "ice giants") for two main reasons. 
 
 First, the solar system's early disk of dust and gas grew more diffuse farther out from the sun. With less material available, it took Uranus and Neptune longer to form. 
 
 Second, this slower formation gave the sun more time to blow hydrogen and helium out of the solar system with its stellar winds— before Uranus and Neptune could grow massive enough to capture it with their gravity. 
 
 "Giant planets form really fast, in a few million years," Kevin Walsh, who studies planet formation at the Southwest Research Institute in Colorado, told Space.com in March. "That creates a time limit because the gas disk around the sun only lasts 4 to 5 million years." 
 
 Scientists agree on this much, but Orton said they have "too many theories" about the migration of Uranus and Neptune, which came next. 
 
 A true-color photo of Uranus (left) and a false color image (right) taken at the turn of 1986 by NASA's Voyager 2 probe. NASA/JPL-Caltech 
 
 One leading idea says the planets coalesced millions of miles closer to the sun, then quickly migrated outward. 
 
 But Orton said the newly detected hydrogen sulfide — and a strange lack of ammonia in the Gemini Observatory readings — suggest the planets actually formed farther out, then moved inward. (The ratio of the two molecules suggests the worlds were once even colder than they are today.) 
 
 To solve the question once and for all, Orton says researchers need to send spacecraft to plunge through the clouds of Uranus, not unlike how the Cassini probe dove into Saturn. The goal: figure out the exact abundances of hydrogen sulfide and ammonia, among other gases, and use the readings to pin the exact birth locations of Uranus and Neptune. 
 
 "We're working on that now," Orton said, referring to a proposal for a new Uranus probe. 
 
 This story has been updated. It was originally published on April 23, 2018, at 6:11 p.m. EDT.
– Scientists using the huge telescope on Hawaii's Mauna Kea volcano have discovered the world's most obvious space joke. "Uranus smells like farts" is an actual, and correct, headline making the rounds, as here and here. But as the BBC explains, it's no joke. It seems the seventh planet from the sun does indeed smell like rotten eggs. Scientists figured this out using the spectrometer on the Gemini North telescope—they found that the planet's clouds are made up mostly of the smelly gas hydrogen sulfide. The discovery, reported in Nature Astronomy, should help astronomers better understand the formation not only of Uranus but of the other outer planets. For one thing, Uranus differs from gas giants Jupiter and Saturn, whose clouds are made up mostly of ammonia ice (and are thus less smelly). "If an unfortunate human were to ever descend through Uranus' clouds, they would be met with very unpleasant and odiferous conditions," says study co-author Patrick Irwin of the University of Oxford in a news release. Not that they'd live long enough to sniff it: "Suffocation and exposure in the (minus 328 degrees Fahrenheit) atmosphere made of mostly hydrogen, helium and methane would take its toll long before the smell." It's likely that Neptune's clouds are similar to Uranus' clouds in makeup, given that those two planets formed farther from the sun than Jupiter and Saturn, notes Space.com. For the record, astronomers generally prefer pronouncing the planet with the accent on the first syllable (YER-in-us), per Universe Today. (Scientists examining 30-year-old images from Uranus found a surprise.)