• The color of the “mists” that surround the planets is determined by the scattering of light from their atmosphere, according to our partner The Conversation.

  • If Neptune and Uranus thus present beautiful shades of blue, Jupiter and Saturn have completely different color atmospheres.

  • The analysis of this phenomenon was carried out by Jake Clark, PhD student in Astronomy at the University of South Queensland (Australia).

Hello, Charles, and thank you very much for your incredibly curious question.

You also wonder if the color of the sky is related to the atmosphere and if the other planets have one.

Before getting carried away to evoke the atmospheres of other planets, I must first talk about what an atmosphere really is.

Earth's atmosphere is divided into different layers © ESA

The atmosphere is normally the outermost layer of a planet.

On rocky worlds like Earth, this is usually the lightest and thinnest layer.

What makes an atmosphere an atmosphere is what it is made of.

It is not made of large chunks of rocks or huge swirling oceans, it is made of gas.

What's in an atmosphere?

Atmospheres can contain a wide variety of gases.

Most of Earth's atmosphere is made up of a gas called nitrogen that doesn't really react with anything.

It also contains a good amount of oxygen, which we need to breathe.

There are also two other important gases, argon and carbon dioxide, and small amounts of many other gases.

It is this mixture of gases that gives the atmosphere of a planet its color.

VIDEO:

The blue “haze” surrounding Earth in space is caused by the scattering of light from Earth's atmosphere.

Earth's atmosphere is made up of gases that tend to bounce blue light in all directions (called scattering) but which pass most of the other colors of light directly.

It is this scattered light that gives Earth's atmosphere its blue color.

Do other planets have a blue atmosphere?

Some of them have one!

The other worlds

The atmospheres of the two ice giants of our solar system, Neptune and Uranus, both feature beautiful shades of blue.

However, these atmospheres are a different blue from ours.

This is due to the huge amounts of a gas called methane.

Uranus's atmosphere (left) is slightly greener than Neptune's (right) © Björn Jónsson / NASA / JPL-Caltech

Jupiter and Saturn, on the other hand, have completely different colored atmospheres.

Ice crystals made up of a chemical called ammonia in Saturn's upper atmosphere give it a pale yellow hue.

The atmosphere of Uranus also contains ammonia, which gives the planet a slightly greener hue than the deep blue of Neptune.

Jupiter's atmosphere shows characteristic brown and orange bands, thanks to gases that can contain the elements phosphorus and sulfur, and perhaps even chemicals called hydrocarbons.

VIDEO:

The Juno spacecraft passing Jupiter in 2017

In some extreme cases, the entire planet could be just one huge atmosphere with no rocky surfaces.

Astronomers and planetologists like myself are still trying to determine if Jupiter and Saturn have rocky surfaces, deep in their atmosphere, or if they are both huge balls of gas.

The Cassini probe captured this striking image of Saturn in 2010 © NASA / JPL-Caltech / Space Science Institute

However, there are planets that have no atmosphere at all!

Mercury, the closest and smallest neighbor to the Sun, is an example.

Its surface is exposed to the vastness of space.

Beyond our solar system

So far I have talked about the atmospheres of the planets in our solar system.

But what about planets in other planetary systems, orbiting other stars?

Well, astronomers have been detecting the atmospheres of these planets (which we call

exoplanets

) for the past 20 years!

It wasn't until last year, however, that astronomers were able to detect the atmosphere of a rocky exoplanet.

The planet is called LHS 3844b and it is so far away that it takes almost 50 years for light to reach us!

LHS 3844b

weighs twice as much as the Earth, and we astronomers thought it would have a fairly thick atmosphere.

But, to our surprise, it has little or no atmosphere!

It could therefore look more like Mercury than Earth.

VIDEO:

Animation showing an artist's view of what the surface of LHS 3844b might look like.

We still have a lot to learn about distant planets and it will take many more years to discover one with an Earth-like atmosphere ripe for life.

OUR “ASTRONOMY” FILE

Perhaps, Charles, could you be the first astronomer to detect an Earth-like atmosphere on another world!

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This analysis was written in English by Jake Clark, PhD student in Astronomy at the University of South Queensland (Australia).


The original article

was translated by Benoît Tonson (with the help of DeepL) and then published on The Conversation website.

Declaration of interests

Jake Clark is a recipient of an Australian Government Research Training Program (RTP) scholarship.

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