We’ve never seen Uranus in such glory until now
It turns out, Uranus isn’t the colour we thought it was. Neither is Neptune, always in Uranus’s shadow.
And it seems Uranus also changes colour – depending on how much methane is around it.
After decades of gazing at them through pictures taken by the pioneering Voyager 2 spacecraft, clearly the two ice giants aren’t quite as they seem.
Uranus, thought to be more green – it also looks like a small greenish dot when viewed through binoculars on Earth – is actually a greenish-blue.
While Neptune, thought to be a brilliant blue, is a similar green-blue. Two green-blue balls billions of miles away, making a lonely orbit around the Sun.
The new findings were made by Professor Patrick Irwin from the University of Oxford and his team, who studied Uranus in detail to create the new, improved images.
And Neptune too.
‘Although the familiar Voyager 2 images of Uranus were published in a form closer to ‘true’ colour, those of Neptune were, in fact, stretched and enhanced, and therefore made artificially too blue,’ said Professor Irwin.
‘Even though the artificially-saturated colour was known at the time amongst planetary scientists – and the images were released with captions explaining it – that distinction had become lost over time.
‘Applying our model to the original data, we have been able to reconstitute the most accurate representation yet of the colour of both Neptune and Uranus.’
Early images of Neptune from Voyager 2 were also strongly contrast enhanced to better reveal the clouds, bands, and winds that shape what we have come to think the planet looks like, scientists say.
The Oxford team used new data from the Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope to re-balance the composite colour images sent back from deep space to create more accurate images of the solar system’s two most distant planets.
The findings also answered another question about Uranus that has been perplexing scientists for decades – why it changes colour during its 84-year journey around the Sun.
It’s all about methane.
It turns out the colour changes depending on how much methane is at the planet’s poles. Unlike all the other planets, Uranus spins on its side, meaning the north pole is facing the Sun for half the year, and the south pole the other half.
At certain times of year the layer of methane ice crystals grows thicker, which absorbs red light, making it appear more green.
‘This is the first study to match a quantitative model to imaging data to explain why the colour of Uranus changes during its orbit,’ said Professor Irwin.
‘In this way, we have demonstrated that Uranus is greener at the solstice due to the polar regions having reduced methane abundance but also an increased thickness of brightly scattering methane ice particles.’
So there you have it. Uranus is green-blue – but greener when there’s an abundance of methane.
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