Oxford scientists reveal what Uranus and Neptune really look like

Many people will think of Neptune as being a rich blue colour, and Uranus more green.

But a new study has revealed that the two ice giants are actually much closer to each other in colour.

Professor Patrick Irwin from the University of Oxford, and his team found that both planets are a similar shade of greenish blue.

Experts suggest the idea that both planets were different colours arose because images of them captured in the 20th century - including by Nasa's Voyager 2 mission, the only spacecraft to fly past these worlds - recorded images in separate colours.

The single-colour images were later recombined to create composite colour images, which were not always accurately balanced to achieve a true colour image.

Prof Irwin said: "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.

"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."

In the new study, the researchers used data from Hubble Space Telescope's Space Telescope Imaging Spectrograph (STIS) and the Multi Unit Spectroscopic Explorer (MUSE) on the European Southern Observatory's Very Large Telescope.

In both instruments, each pixel is a continuous spectrum of colours, meaning observations from them can be processed to determine the true apparent colour of Uranus and Neptune.

The study also found that Neptune has a slight hint of additional blue, which the model reveals to be due to a thinner haze layer on that planet.

The study also provides an answer to the long-standing mystery of why Uranus's colour changes slightly during its 84-year orbit of the sun.

Dr Heidi Hammel, of the Association of Universities for Research in Astronomy (AURA), who has spent decades studying Neptune and Uranus but was not involved in the study, said: "The misperception of Neptune's colour, as well as the unusual colour changes of Uranus, have bedevilled us for decades.

"This comprehensive study should finally put both issues to rest."

The findings are published in Monthly Notices of the Royal Astronomical Society. Hear all the latest news from across the UK on the hour, every hour, on Greatest Hits Radio on DAB, smartspeaker, at greatesthitsradio.co.uk, and on the Rayo app.