Ask Ethan: Why Does Mars Have A Bright, Red Sky?
“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 incredibly bright sky and incredibly blurred mountains! How can you explain it?”
Before we ever sent a spacecraft to Mars, we knew that its atmosphere was thin and sparse, and that it was made mostly of carbon dioxide gas. We anticipated that the sky, therefore, would appear like a much fainter, thinner, sparser version of our own, mostly transparent atmosphere. But that isn’t how things worked out at all! Instead, the atmosphere on Mars appears bright, reddish, and (depending on conditions) somewhat varied in color. This isn’t due to false coloration issues, as some might think, but rather to the fact that the Martian atmosphere is rife with the same thick, desert-like dust that covers the surface of the planet! In addition, the mountains and geologic features in the distant backgrounds of images from Mars’ surface appear obscured, as though they’re in some kind of fog, and sunsets appear a bizarre blue. Why does this happen?
Believe it or not, the answer is all part of a simple, compelling, and self-consistent picture. (And no, it’s not because they’re color-corrected Earth photos!) Come get the full story on this edition of Ask Ethan!