why blue sunset on mars

                    Why Mars have blue sunset 

the case of Mars, its more of a local phenomenon; dust particles and not atmospheric composition which dominate scattering in Mars.

Compared to Mars, Earth has a relatively thick atmosphere, so most of the atmospheric scattering occurs when light is incident on an air molecule, known as Rayleigh scattering. Rayleigh scattering occurs when the object a photon scatters off (the air molecule) is much smaller than the wavelength of the photon. The closer the wavelength is to the size of the molecule, the more likely it is to scatter. This means that red wavelengths (which are the longest in visible spectrum) don’t scatter with air molecules much, while blue wavelengths (which are the shortest) tend to scatter a lot. This is why the sky appears blue, since so much of the blue light is scattered.

When the Sun is low in the sky, it’s light has to travel a long path through the atmosphere to reach you. As the light travels through the atmosphere some of the photons are scattered off the air molecules. When the photons scatter off air molecules, they scatter randomly in all directions, so usually when a photon scatters, most of it scatters away from your line of sight. Since blue photons scatter much more often than red ones (blue wavelength is shorter and more comparable to the size of atmospheric gas molecules on earth), much of the blue light is scattered away. This leaves red photons to reach your eye. Hence the Sun looks red when low in the sky. When the Sun is overhead, the path it takes to reach you is much shorter, so only a bit of the blue light is scattered. So the Sun looks yellow.

Now, Mars has a much thinner atmosphere (1% of Earth's), so the amount of Rayleigh scattering is much less. But Mars also has a dry, dusty surface, and a weaker surface gravity, so the atmosphere of Mars is often filled with fine dust particles (if you watched the movie Martian, you can recall it). These particles are larger in size than the main atmospheric gases of Mars's atmosphere, also more comparable in size to the larger wavelengths of visible light, so most of the light is scattered by Mie scattering. On the contrary, Rayleigh scattering due to atmospheric composition dominates in the case of earth. While, for Mars, it is the larger dust particles which play the major role and push the scattering characteristics to the Mie region. One of the main differences between Rayleigh and Mie scattering is that Rayleigh scattering tends to occur in all directions, but Mie scattering varies with scattering angle. Also, good to know that the scattering cross-section in Mie scattering region has oscillatory characteristics. Effectively, what this means is that longer wavelengths (reds) tend to scatter more uniformly, while shorter wavelengths (blues) tend to scatter at slight angles. This further means that the blue light tends to be deflected less than red light which implies Mars can have a dusty red daytime sky, and a blue sunset.

Mie scattering does occur on Earth as well, but since Mie scattering is less efficient than Rayleigh scattering it’s never strong enough to give us a blue sunset. It can (rarely) produce a blue moon. It happened more than 100 years ago though; due to the volcanic eruption of Krakatoa in 1883, which sent so much ash into the atmosphere it produced brilliantly red sunsets and visibly blue moons all across the globe for nearly two years. https://en.wikipedia.org/wiki/Blue_moon#Visibly_blue_moon

As a result, the phrase “once in a blue moon” came to mean a rare occurrence.

  In short

Rayleigh scattering is dominated in shorter wavelength while light go through atmosphere including scatterers smaller than light wavelength. this is why some objects seem blue like sky or Mars sunset.

For the red sunsets, the color of the sun itself appears to change, first to orange and then to red since even more of the short wavelength blues and greens are now scattered and only the longer wavelengths(reds, oranges) are left to be seen.