Uranus and Neptune
Although the familiar Voyager 2 images of Uranus were published in a form closer to true colour, those of Neptune were stretched and enhanced, making them too blue
In the summer of 1989, from a remote expanse of our Solar System where sunlight is merely I a tepid glow, NASA’s Voyager 2 spacecraft radioed to Earth humankind’s very first images of Neptune. The pictures revealed the Sun’s outermost planet was a stunning deep-blue orb. In contrast, Uranus – Neptune’s planetary neighbour and the first to be discovered with a telescope – appeared noticeably paler. Both seemingly twin worlds have a lot in common. They’re roughly the same size, almost equally massive and are both enveloped with deep atmospheres made of similar materials. So why were the two orbs different shades of blue? This is a question that has puzzled scientists for decades. Now a fresh analysis of Voyager 2’s images shows both ice giants are in fact a similar shade of greenish blue, which is the most accurate representation yet of the planets’ colours.
The images Voyager 2 recorded of Uranus and Neptune were in single colours that were combined to create composite images that showed the planets to be cyan and azure respectively. While Uranus’ published pictures were processed close to its true colour, early Neptune images had been “stretched and enhanced” to display its clouds, bands and winds, “and therefore made artificially too blue,” study lead Patrick Irwin, a planetary physicist at Oxford 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 over time.”
To resolve the misconception, Irwin and his colleagues used new images from NASA’s Hubble Space Telescope and the European Space Agency’s Very Large Telescope, whose instruments capture a rich spectrum of colours in each pixel. Processing them de
