In contrast to the red and yellow hues that fill the sky during a sunset on Earth, watching the sun go down on Mars is a much bluer experience.
Curiosity, NASA’s Mars rover, observed the sunset above in April, snapping an image with its Mast Camera. This is the first Martian sunset Curiosity has observed in color.
Because of the fine dust that permeates the thin atmosphere on Mars, blue light comes through more efficiently than longer wavelength colors of light like red. So when all the colors of sunlight shine through the atmosphere, blues stays closer to the direction of the sun. Because sunlight has longer to travel through the atmosphere when the sun on the horizon, the blue effect is more pronounced at sunset than during the middle of the day.
[h/t: USA Today]