Mars Has Blue Sunsets

As the sun dips below the horizon on Earth, our sky is painted in fiery reds and oranges. This happens because our atmosphere's tiny gas molecules are excellent at scattering short-wavelength blue light, leaving the longer red wavelengths to reach our eyes. On Mars, however, the physics are flipped on their head. The thin Martian atmosphere is filled with fine, reddish dust particles. These particles do the opposite of our air molecules: they scatter long-wavelength red light across the sky but allow shorter-wavelength blue light to penetrate directly through when looking toward the setting sun.

This otherworldly phenomenon was first photographed by NASA's Viking 1 lander in 1976 and has since been beautifully captured by rovers like Spirit, Opportunity, and Curiosity. The images they send back show a sun that appears only about two-thirds the size it does from Earth, surrounded by a distinct, eerie blue glow. While the daytime sky on Mars is a hazy, butterscotch color due to the suspended dust, the sunset provides a brief and striking moment of cool blue in the twilight of the Red Planet.