The long-awaited moment when the Curiosity rover took some time away from science to admire the scenery is finally here. We are now able to enjoy the marvelous sunset on Mars.
Martian sunset is remarkable because it is blue. The reason for this unusual color is the same as for red sunset on the Earth and is called Rayleigh scattering. There is a misconception that the blue sky on the Earth is due to the presence of oxygen in the air or even the ozone layer. In fact, the composition of the atmosphere here is less significant than its density. It is the gas density that leads to the scattering of white sunlight and coloring of the sky.
The difference between the color of the sky at noon and at sunset is in the volume of the atmosphere that sunlight travels through. Martian atmosphere is a hundred times thinner than on Earth, but when the Sun is near the horizon, the light overcomes a layer of atmosphere that is thirty times thicker than at noon.
Additional coloring of Martian sky is given by the dust that is constantly hanging in the atmosphere. Apparently it was that orange color plus the blue that gave the slightly greenish tint on the photo. Although, I have to say that the weather is quite clear, and this is the best visibility I have seen in all time of Curiosity working on Mars. For the first time we can see the stones on the hillside nearly 30 km away from the rover.
However, there is still a lot of dust in the sky. You can see how a mountain ridge gets lost in the haze.
At best, it is visible from 50 kilometers. Current clear sky explains why the top of the sunset panorama is almost black. When the Sun is at the zenith, it should be as black as the sky on the Moon or on the Earth at an altitude of 30 km and higher.
Observations made by Viking program show how the color of the sky changes depending on the amount of dust.
Let’s go back to the color of the sunset. Thanks to modern technology, we can see the dawn from space. You can clearly see the orange color of the clouds on the border of the day and night on the last image from Electro-L.
Looking at Mars with the Hubble telescope, we can similarly see a blue band that encircles Mars at the edge of the illuminated disk.
Interestingly enough, that blue band is not always visible on shots of Mars. Apparently the reason for that is in the seasonal variations of the atmospheric density. Depending on time of the year, the reserves of the Martian ‘air’ may fall to 1 /150 of the Earth’s reserves. The rest freezes to the state of dry ice at the poles.
Curiosity had already taken a few shots of sunset on Mars, but did it in black and white with its navigational camera. I had to borrow the colors from another shot made by Spirit for this video, but in the end I think it turned out ok.
The blue sky doesn’t come as much of a surprise to us. But what is really incredible, it’s the blue setting Sun. As we know from our experience on the Earth, at dawn both the sky and the disk of the Sun change color.
Unfortunately, Curiosity does not risk taking images of the Sun directly, so as not to damage the camera matrix, but it was able to capture the solar flare, which was blue.
Post by zelenyikot.