Why can the red planet offer a blue sunset?

The images of Mars have accustomed us to reddish soils and dusty skies. Yet, near the setting sun, a bluish glow may appear. A photograph of Mars Pathfinder shows this color variation, far removed from the red with which the planet is spontaneously associated.

It is not necessary to look for a cloud of ice behind this blue. Atmospheric dust itself plays a role. The properties of its particles change the way different colors of light are absorbed and dispersed. Some of the blue light is particularly visible near the direction of the Sun.

At sunrise and at bedtime, the light passes through more dust before reaching the observer. This geometry makes the effect more apparent. The whole sky does not necessarily become a large blue dome. The contrast is more subtle: the material that contributes to the reddish aspect of the celestial landscape can also give it, in the right place, its most unexpected shade.