Why are the planets different colours?
Of the eight planets in our Solar System, only two can’t be seen unaided from Earth – Uranus and Neptune. And even then, unless you’re observing through a telescope, the physical appearance of almost all planets will be difficult to perceive. Except of course Earth’s neighbouring planet, Mars, which even ancient cultures correctly documented as being red, as its orange-red glow is distinguishable from Earth.
Space missions and scientific advancements in the last century have greatly improved our perception of the planets, including those closest and farthest away from the Sun. As a result we are now finally able to identify a planet’s true colour and – more importantly – understand why it appears as such.
The colour of each planet is determined by what they made up of, and in some instances, how their atmospheres absorb and reflect light from the Sun.
The four terrestrial planets, which have solid rock surfaces, are mostly grey or reddish-brown in appearance due to elements such as iron found on the surface. However, the surface of Venus is difficult to detect from space, as a dense atmosphere and thick clouds of acid surround it. The sulphur present in the clouds reflects the light and gives Venus its noticeable yellow colouring. A similar principle applies when it comes to determining the colours of the four gas giants. Uranus and Neptune, for example, appear to us as blue because methane gas present in their atmospheres absorbs red light, enabling them to only reflect blue.
Mercury is not the blazing ball of fire you might expect. In fact, its appearance closely resembles Earth’s Moon. Its cratered surface appears greyish-brown in colour due to the composition of its rocky surface, which is impacted by particles and solar winds. Temperatures fluctuate to extremes, thanks to its thin atmosphere.
Volcanic activity has shaped the surface of Earth’s largest neighbouring planet, Venus. Its dry, barren landscape is made up of greyish rock. From space, however, you’ll notice thick, swirling yellow and white clouds, which are made up of sulphuric acid – a result of the planet’s dense atmosphere.
Earth is the only habitable planet in our Solar System, thanks to its unique atmosphere. It is also the only planet to have liquid water on its surface, which is key to supporting life. From space you’ll see vast blue oceans, green and brown land as well as thick white cloud cover.
Mars is known as the Red Planet, so called because of its colouring, which is caused by high levels of iron oxide found on the surface. Although dry and dusty, temperatures on Mars are similar to those on Earth, but the planet is also plagued by powerful dust storms, a consequence of its thin atmosphere.
Gas giant Jupiter is the largest in our Solar System. Made up mostly of hydrogen and helium, like the Sun, its structure resembles that of a star. Ice crystals and other elements help form thick bands of red, brown, yellow and white clouds, which encircle the entire planet. Its famous red spot can also be seen from Earth through telescopes.
The lightest but second-largest planet in the Solar System. This gas giant is mostly made up of hydrogen and helium, but traces of ammonia,
phosphine, water vapour and hydrocarbons in its atmosphere give the planet its distinct yellowish-brown colour. Saturn’s famous rings, which are primarily made up of water ice, share a similar hue, but also vary in colour depending on density and the presence of other materials.
Although classified as a gas giant, an icy layer of cloud covers the planet Uranus. The coldest planet in our Solar System, temperatures at cloud level drop to below -220°C (-364°F). Methane in its atmosphere gives Uranus its distinct turquoise appearance; as red light is absorbed, only green-blue light is reflected.
Smallest of the four gas giants, Neptune shares a lot of physical similarities with its neighbour Uranus, including its blue colouring. It’s considered the windiest planet, with speeds recorded at around 2,414km/h (1,500mph). Extreme storms are also known to occur in its atmosphere and the planet also features a giant storm spot like Jupiter.
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