For more than 30 years, the public have believed Neptune is a brilliant shade of dark blue, quite different in colour from neighbour Uranus.
But a new study debunks this by finally revealing what the two ice giants really look like – and they’re far closer in colour than previously thought.
Neptune is actually a pale bluish-green or ‘cyan’, similar to Uranus and much lighter than the famous deep blue in images from the Voyager 2 spacecraft.
The study’s new images provide the closest approximation yet of what we would see with the naked eye if we were somehow able to travel to these planets.
More than 30 million miles away, they are the two most distant known major planets in our solar system.
Neptune is known for being a rich blue and Uranus green – but the two ice giants are actually far closer in colour than typically thought. Neptune is actually not as deep blue as is often thought and has a colour much more similar to that of Uranus – pale bluish-green or ‘cyan’
The study has been led by Professor Patrick Irwin from the University of Oxford’s Department of Physics.
‘We thought it worthwhile to point out what the true colours of these planets actually are,’ he told MailOnline.
‘None one of us will ever see these planets from an orbiting spacecraft, and the planets are very hard to observe with ground-based telescopes so very, very few people have any insight into what these planets should actually look like.’
Uranus and Neptune, the seventh and eighth planets in our solar system, are the only two ice giants in the outer solar system.
They are mainly made up of a hot dense fluid of icy materials – water, methane, and ammonia – above a small rocky core.
It was NASA’s Voyager 2 spacecraft, launched in 1977, that took photos of Uranus and Neptune during flybys of both the planets – in 1986 and 1989, respectively.
Although the spacecraft was a monumental success, it actually resulted in the modern misconception of what the two planets look like.
That’s because Voyager 2 recorded multiple images with different colour filters which had to be combined to create composites.
The thing is, the images were not always accurately balanced to achieve a ‘true’ colour composite, and – particularly in the case of Neptune – were often made ‘too blue’.
Not quite accurate: It was in 1989 that NASA’s Voyager 2 spacecraft provided the first close-up images of Neptune. In fact, Neptune is a paler shade of greenish blue, closer to Uranus
Voyager 2 is pictured here at the Kennedy Space Center in Florida on August 4, 1977, prior to launch 16 days later
In addition, the early Neptune images from Voyager 2 had their contrast strongly enhanced to better reveal the planet’s features such as clouds, bands and winds.
‘In our paper we show that if you combine the images together to produce something close to “true” colour, these features look rather “washed out” and indistinct,’ Professor Irwin told MailOnline.
‘The Voyager team saw this too and it was thus decided to combine the images together in a way that better communicated the scientifically interesting features.
‘This was mentioned when the images were released but the distinction has been lost over time so now most people (including planetary scientists) think Neptune is dark blue.
To reveal the true colours, Professor Irwin and colleagues used data from Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope in Chile.
Data from the instruments let the team re-balance the composite colour images recorded by the Voyager 2 camera, and also by the Hubble Space Telescope’s Wide Field Camera 3 (WFC3).
This revealed that Uranus and Neptune are actually a rather similar shade of greenish blue or ‘cyan’ – commonly described as the colour of shallow water over a sandy beach.
The main difference is that Neptune has a slight hint of additional blue, due to a thinner haze layer on that planet, but nothing like we had been led to believe.
Professor Irwin said the Voyager team of the late-1980s ‘did the right thing’ and is not suggesting that the early release Voyager images were misleading.
‘However, we should never overlook that some of these images were processed in a way that is not strictly true colour,’ he told MailOnline.
Although Uranus looks similar to how it was perceived in the original Voyager 2 snaps, the new study did yield interesting insights about the seventh planet.
The study answers the long-standing mystery of why Uranus’s colour changes slightly during its 84-year orbit of the sun.
Uranus as seen by Hubble Space Telescope’s Wide Field Camera 3 (WFC3) from 2015-2022. During this sequence its north pole, which has a paler green colour, swings down towards the sun and Earth
Earth’s axis is tilted about 23 degrees. But Uranus tilts around 98 degrees – which gives the impression the planet is rotating on its side
This image from the team’s paper shows radiance spectra of Uranus and Neptune which reveals their true colour
Uranus is unique in the solar system because of its axis, which is almost parallel to its orbit.
While Earth’s axis is tilted about 23 degrees, Uranus tilts around 98 degrees – which gives the impression the planet is rotating on its side.
Measurements have already showed that Uranus appears a little greener at its solstices (i.e. summer and winter), when one of the planet’s poles is pointed towards the sun.
But during its equinoxes – when the sun is over its equator – it has a somewhat bluer tinge.
Researchers found that the polar regions of Uranus are more reflective at green wavelengths than at blue wavelengths.
This is because methane, which is green-absorbing, is about half as abundant near the poles than the equator.
The ice giants Uranus and Neptune remain a ‘tantalising destination’ for future robotic explorers, building on the legacy of Voyager 2, the research team say.
‘A mission to explore the Uranian system – from its bizarre seasonal atmosphere, to its diverse collection of rings and moons – is a high priority for the space agencies in the decades to come,’ said co-author Leigh Fletcher at the University of Leicester.
‘Studies like this, showing how Uranus’ appearance and colour has changed over the decades in response to the weirdest seasons in the Solar System, will be vital in placing the discoveries of this future mission into their broader context.’
The new study has been published in Monthly Notices of the Royal Astronomical Society.
HOW DOES URANUS’S MAGNETIC FIELD COMPARE TO EARTH’S?
A study analysing data collected more than 30 years ago by the Voyager 2 spacecraft has found that the Uranus’s global magnetosphere is nothing like Earth’s, which is known to be aligned nearly with our planet’s spin axis.
A false-color view of Uranus captured by Hubble is pictured
According to the researchers from Georgia Institute of Technology, this alignment would give rise to behaviour that is vastly different from what’s seen around Earth.
Uranus lies and rotates on its side, leaving its magnetic field tilted 60 degrees from its axis.
As a result, the magnetic field ‘tumbles’ asymmetrically relative to the solar wind.
As a result, the magnetic field ‘tumbles’ asymmetrically relative to the solar wind.
When the magnetosphere is open, it allows solar wind to flow in.
But, when it closes off, it creates a shield against these particles.
The researchers suspect solar wind reconnection takes place upstream of Uranus’s magnetosphere at different latitudes, causing magnetic flux to close in various parts.