Ask Ethan: Why Does Mars Have A Bright, Red Sky?
We know that it’s ‘the red planet’ because of the iron in its soil. But why, with such a thin, carbon dioxide atmosphere, is the martian sky so red and bright?
We can learn an awful lot about a world by looking at its atmosphere. On Earth, for example, the optical properties of sunlight passing through our atmosphere tell us about its composition, reflectivity, density, and much more. If our atmosphere were significantly thinner and less dense, the sky would be less blue, sunsets would be less red, and the sky, overall, would be far less bright. When we look at Mars, we find that it has just 0.7% of Earth’s atmospheric density, telling us that even with Mars’ reduced gravity, the mass of its atmosphere is very thin and sparse compared to our world. So why, then, when the Mars rovers and landers have taken pictures, does the Martian sky appear so bright? That’s the question of Vitaly Nasennik, who wants to know:
We, the physicists, know, that the brightness of the sky is caused by the light of the Sun, which is scattered on the matter of the atmosphere. The brightness of the sky directly corresponds to the mass of matter in the atmosphere. […] But what can we see on the pictures from the Curiosity, Spirit & Opportunity rovers? The…
