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Why are Uranus and Neptune different colours?

Uranus and Neptune have plenty of similarities, and like siblings, the two are often compared to each other.

The pair of ice giants are the furthest two major planets in our solar system, and they are about the same size, roughly 15 times the size of Earth.

Both planets spin much faster than Earth, completing their daily rotations in less than 17 hours.

Near their superheated cores, it may even rain diamonds.

But we had better not don’t call them twins just yet.

The ice giants appear blue because of the methane in their atmospheres. Methane reflects blue light and absorbs red light. Pictured: Uranus on the left and Neptune on the right. NASA/JPL-Caltech

Neptune, rather interestingly, is a vibrant shade of cobalt blue, whereas Uranus has a pale green tint.

A recent study suggests that the variance in their hues may due to a hazy layer where methane reacts with sunlight found in both planets’ atmospheres. The milky layer is twice as opaque on Uranus than it is on Neptune, which would make Uranus appear more pale.

The only spacecraft to study the furthest planets in our solar system, NASA’s Voyager 2, was launched in 1977 and reached Uranus in 1986 and Neptune in 1989.

The spacecraft gave astronomers an up-close look at the ice giants for the first time.

The thick, freezing, and gassy atmospheres of Uranus and Neptune contain a mixture of hydrogen, helium, and methane. In the planets’ lower atmospheres, methane absorbs red light and reflects blue light, giving both icy worlds their deep blue undertones.

However, patches of chemicals create haziness throughout the atmospheres of both faraway worlds. These cloudy-looking layers occur where the sun’s ultraviolet radiation breaks down aerosols. This photochemical process occurs on Venus, Earth, Jupiter, and Saturn as well.

Donna the Astronomer

I am a keen astronomer lucky enough to live and work in Coonabarabran the Astronomy Capital of Australia! I am a ‘Drover’s Brat’ and discoverer of a couple of comets and asteroids. I operate Milroy Observatory and can show you how to best integrate dark sky experiences into your tourism, farm stay or AirBnB business.

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