Neptune images were made ’artificially too blue’ when processed by NASA

The planet Neptune has for decades been depicted in picture books and on the NASA website as a deep shade of blue, but scientists have now said this view is wrong.

The Voyager 2 photo of Neptune, left, and the new, more accurate image.

Named after the Roman god of the sea, the planet Neptune has for decades been depicted in picture books and on the NASA website as a deep shade of blue, but scientists have now said that this view is wrong.

The solar system’s outermost planet is actually a far lighter shade of greenish blue and is much closer in colour to Uranus, new analysis has found.

The image of Neptune as much darker and bluer than Uranus was cemented when pictures were sent back by the Voyager 2 probe after it flew by the two ice giants in 1986 and 1989.

Scientists from the University of Oxford have now said that the images released of Uranus, showing it as an almost featureless orb of light greenish blue, were close to the planet’s “true” colour but the images of Neptune were made “artificially too blue” when processed by NASA. The contrast was also raised to show the planet’s clouds in greater detail, deepening the shade of the planet.

When Voyager 2 flew by Neptune and Uranus it took a series of single-colour pictures “later recombined to create composite colour images”, the researchers said. They added: “[These] were not always accurately balanced to achieve a true colour image and, particularly in the case of Neptune, were often made too blue.”

Scientists working on the Voyager mission explained at the time that the true colour of Neptune was lighter, but the image of a deep-blue planet stuck.

Professor Patrick Irwin, a physics lecturer at the university, said: “Even though the artificially saturated colour was known at the time among planetary scientists – and the images were released with captions explaining it – that distinction had become lost.”

In an analysis published in the journal Monthly Notices of the Royal Astronomical Society, the Oxford researchers took data from instruments on the Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope in Chile.

They collected data across the spectrum, allowing scientists to reconstitute the most accurate representation of the colour of Neptune and Uranus. It revealed both planets are a similar shade, but Neptune is slightly bluer because of a thinner layer of haze.

The Times