Neptune isn’t as blue as we thought it was
An analysis of photos taken by Voyager 2 in the 1980s shows that Neptune and Uranus have a similar pale blue hue as perceived by the human eye
By Alex Wilkins
5 January 2024
The original Voyager 2 photo of Neptune (left) and the reprocessed image from the new study (right)
Patrick Irwin
Neptune’s true colour is a pale greenish-blue similar to that of Uranus, contrary to popular images that show it to be a much deeper shade of blue.
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NASA’s Voyager 2 spacecraft flew past the outer planets in the 1980s and sent back photos showing that Uranus and Neptune were markedly different colours.
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This is puzzling, given their similar size, mass and chemical make-up. Models of the planets’ atmospheres can explain some of the variation – such as a “haze layer” that is thicker on Uranus and reflects more white light, making the planet appear lighter – but these don’t fully explain why the planets should have such different hues.
Now, Patrick Irwin at the University of Oxford and his colleagues have processed the Voyager 2 images to show how the human eye might see the planets.
The original photos of Neptune taken by Voyager 2 had an enhanced contrast ratio to highlight hard-to-see atmospheric features. Along with the way that the colours were balanced to make a final composite image, this made the planet appear bluer.
