Scientists work out why Neptune and Uranus are different shades of blue

The two planets are similar in size, mass and atmosphere, yet Neptune is distinctly darker than its neighbour Uranus.

New research led by Professor Patrick Irwin, from the University of Oxford’s Department of Physics, suggests that a layer of haze that exists on both planets is behind the different hues of blue.

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Explaining the study, Professor Irwin said: “This is the first model to simultaneously fit observations of reflected sunlight from ultraviolet to near-infrared wavelengths.

“It’s also the first to explain the difference in visible colour between Uranus and Neptune.”

Uranus and Neptune. Picture: NASA/JPL-Caltech/B. Jónsson

Neptune from Voyager 2. Picture: NASA/JPL

Uranus as seen by NASA Voyager 2. Picture: NASA/JPL-Caltech

The model involves three haze layers at different heights in the atmosphere of each planet.

The middle layer is found to be thicker on Uranus than on Neptune, affecting the colour of the two planets.

On both planets, methane ice condenses on the particles in the middle layer, forming a shower of methane snow that pulls the haze particles deeper into the atmosphere.

Hydrogen sulphide ice then forms a separate, deeper layer of haze.

Neptune has a more active, turbulent atmosphere than Uranus, meaning more of the haze is removed while keeping the planet’s haze layer thinner than on Uranus, making Neptune appear bluer.

In contrast, excess haze on Uranus builds up in the planet’s stagnant, sluggish atmosphere – giving it a lighter tone than Neptune.

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This story was written by Liam Rice, he joined the team in 2019 as a multimedia reporter.

Liam covers politics, travel and transport. He occasionally covers Oxford United.

Get in touch with him by emailing: Liam.rice@newsquest.co.uk

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