Sunsets on earth are usually orange. But in this eerily beautiful image of the Martian surface, the setting sun has a bluish hue. The sunset on planet Mars is blue because it has its fair share of dust storms. This image was taken in between dust storms when some of the fine particles of Martian dust were still in the air. These fine particles are able to disperse light on the left of the VIBGYOR spectrum i.e Blue rather than orange, or in other words, light with a shorter wavelength.
But stop reading this and look at the picture for a moment. We are seeing the sunset on an alien planet. How exciting is that?
Image credits: NASA/JPL-Caltech/MSSS/Texas A&M Univ. (Image has undergone a slight adjustment for vibrance as the Curiosity Mastcam is less sensitive to blue than human eyes)