Astronomers discover why Uranus and Neptune are different colours

The thick haze surrounding Uranus may account for why it has a paler hue than Neptune.

uranus neptune
Published: July 29, 2022 at 8:30 am
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The atmospheres of Uranus and Neptune are remarkably similar in composition, consisting of mostly hydrogen, with some helium and a little methane, which gives them both their blue colour.

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Yet despite this, the two ice giant planets are noticeably different in hue, with Neptune a deep royal blue while Uranus is a pale turquoise.

Indeed, images captured during the Voyager mission and by the Hubble Space Telescope - among others - have revealed the different azures of both planets in remarkable clarity over the years.

A dark storm spotted on Neptune by the Hubble Space Telescope. Credit: NASA, ESA, STScI, M.H. Wong (University of California, Berkeley) and L.A. Sromovsky and P.M. Fry (University of Wisconsin-Madison)
A dark storm spotted on Neptune by the Hubble Space Telescope. Credit: NASA, ESA, STScI, M.H. Wong (University of California, Berkeley) and L.A. Sromovsky and P.M. Fry (University of Wisconsin-Madison)

After years of wondering what could be causing the difference in colour between Uranus and Neptune, a new set of observations from the Gemini Observatory might finally explain it.

By looking at the planets in many wavelengths, astronomers were able to observe the different layers of the Uranus and Neptune's atmospheres.

Both are covered by a layer of haze, which the new study found extends much deeper than previously thought.

An image of Uranus captured by the Hubble Space Telescope in 2003. Credit: NASA, ESA, and M. Showalter (SETI Institute)
An image of Uranus captured by the Hubble Space Telescope in 2003. Credit: NASA, ESA, and M. Showalter (SETI Institute)

The study also showed that Uranus’s haze is much thicker than Neptune's, effectively whitening the planet and making it appear paler.

"We hoped that developing this model would help us understand clouds and hazes in the ice giant atmospheres," commented Mike Wong from the University of California, who took part in the study.

"Explaining the difference in colour between Uranus and Neptune was an unexpected bonus."

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www.gemini.edu

Authors

Elizabeth Pearson
Ezzy PearsonScience journalist

Ezzy Pearson is the Features Editor of BBC Sky at Night Magazine. Her first book about the history of robotic planetary landers is out now from The History Press.

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