Explained: Why Neptune and Uranus appear in different colours

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Neptune and Uranus have much in common. They have similar masses, sizes and atmospheric compositions. But their appearances are in different shades of blue. 

At visible wavelengths, Neptune is a rich, deep azure hue while Uranus is a distinctly pale shade of cyan.

Why do Uranus and Neptune appear in different colours?

The haze around Uranus is thicker than that around Neptune. Due to this, Uranus’s atmosphere has a lighter appearance than Neptune’s.

Without this haze in either planetary atmosphere, astronomers believe both planets would be almost identically blue.

Why is the haze thicker on Uranus?

There are three aerosol layers in the atmospheres of Neptune and Uranus. The key layer that affects the colours is the middle layer. The middle layer is a layer of haze particles that is thicker on Uranus than on Neptune.

On both planets, methane ice condenses onto the particles in this middle layer pulling the particles deeper into the atmosphere. 

But because Neptune has a more active, turbulent atmosphere than Uranus does, the researcher believes Neptune’s atmosphere is more efficient at churning up methane particles into the haze layer. 

This removes more of the haze and keeps Neptune’s haze layer thinner than it is on Uranus with the result that the blue colour of Neptune looks stronger.

Source: The post is based on the article “Explained: Why Neptune and Uranus appear in different colours” published in Indian Express on 2nd June 2022.