Why is Mars Red? Why Are Some Images Blue?
Mars is known as the Red Planet because of iron oxide (like rust) in its soil. The planet's distinctive reddish hue is visible from Earth even without the aid of a telescope. The ancient Romans named it for their God of War (Ares in Greek mythology).
So what's with the blue twilight?
Just as colors are made more dramatic in sunsets on Earth, Martian sunsets would appear bluish to human observers watching from the red planet. Fine dust makes the blue near the Sun's part of the sky much more prominent, while normal daylight makes the Red Planet's familiar rusty dust color more prominent.
"The colors come from the fact that the very fine dust is the right size so that blue light penetrates the atmosphere slightly more efficiently," said Mark Lemmon of Texas A&M University, College Station, a science team member of the Curiosity rover mission. "When the blue light scatters off the dust, it stays closer to the direction of the Sun than light of other colors does. The rest of the sky is yellow to orange, as yellow and red light scatter all over the sky instead of being absorbed or staying close to the Sun."