Why Does Mars Have Blue Sunsets?

NASA's Mars Curiosity rover recorded the sunset in the video above on this day four years ago.However, while it looks a bit like a sunset on Earth there are several fascinating differences, not least the colours involved.

In direct contrast to Earth, Mars' sky is red while its sunset appears to be blue.

So why does this occur? Well, Mars' atmosphere is very different to Earth's – its pressure is equivalent to about 1 percent of Earth's. It is made of carbon dioxide and has a lot of dust. This dust tends to scatter red light so that the sky appears reddish, while letting blue light wavelengths through. On Earth, it is the other way around. Blue light bounces off air molecules giving our sky its colour.

At sunset, light has a greater distance to travel within the atmosphere, so it scatters more, making the colours we see more vivid. On Earth, reds are amplified by ash from volcanoes and dust from fires. On Mars, we get a cool blue hue when the Sun was near the horizon, the time when its light passes through the greatest depth of atmosphere and dust.

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