Maunakea observatory confirms foul-smelling gas in Uranus’ clouds

  • An infrared composite image of the two hemispheres of Uranus obtained with Keck Telescope adaptive optics. (Lawrence Sromovsky, University of Wisconsin-Madison/W.M. Keck Observatory)

Astronomers using the Gemini Observatory on Maunakea have confirmed what has been speculated for years: Uranus stinks.

Spectroscopic analysis of the seventh planet in our solar system has revealed that one of the primary components of Uranus’ clouds is hydrogen sulfide, the same gas that lends rotten eggs their foul smell.


Glenn Orton, senior research scientist at NASA’s Jet Propulsion Laboratory and a member of Gemini’s research team, said the discovery was a coup for not only astronomy, but for laboratory spectroscopy as a whole.

The discovery, Orton said, was a long time coming. Infrared light was captured by the Gemini North telescope on Maunakea between 2009 and 2010. However, it wasn’t until more recently that researchers were able to subject that data to a spectroscopic analysis to confirm the planet’s gaseous composition.

“We had to wait for there to be lab data on hydrogen sulfide,” Orton explained. When the data from Uranus was first gathered, no research had yet been conducted on the spectral signatures of various gases — that is, how the wavelength of light is altered when reflected or emitted by certain gases, including hydrogen sulfide.

When the spectral signature of hydrogen sulfide had been determined, the Gemini team realized they could use that information to determine the composition of Uranus’ clouds. Using Gemini’s near-infrared integral field spectrometer — an instrument originally designed to study distant black holes — the research team was able to identify a hydrogen sulfide signature in a sample of reflected sunlight in Uranus’ atmosphere, putting a rest to a long-standing point of contention in astronomy.

Astronomers long have been split on whether the dominant component of Uranus’ clouds was hydrogen sulfide or ammonia ice, the latter of which composes the majority of the upper clouds of Jupiter and Saturn.

The revelation, Orton said, has significant ramifications for the origins of Uranus.

“If it were formed where it is now, it would have less sulfur than we can see it has now,” Orton said. “This is a smoking gun that demonstrates Uranus was formed somewhere else.”

All of the solar system’s gas giants — Jupiter, Saturn, Uranus and Neptune — have been theorized to have been formed farther away from the sun and have since migrated inward.

Orton said Neptune, the farthest planet from the sun, is thought to have a similar atmospheric composition to Uranus, but confirming it might be more difficult than the Uranus discovery. Because Neptune is so far away, any infrared light samples from the planet would be extremely faint.

Peter Michaud, public information and outreach manager for the Gemini Observatory, said the Uranus revelation was “on the edge of doability,” while Orton said learning more about Neptune might have to wait until a probe can be sent to the distant planet.


No human will likely ever get to smell the air of Uranus firsthand — in addition to a 1.6 billion-mile trip at minimum, a visitor to the planet would have to contend with extreme cold and an unbreathable atmosphere. But thanks to Gemini’s discovery, anyone with an expired carton of eggs can experience the stench of Uranus, the smelliest place in the solar system.

Email Michael Brestovansky at

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