Nothin' but blu-ue skies, do I see!

Blue skies were expected on Mars prior to the Viking landings (I have a whole series of Astronomy magazines from 1974-75 containing illustrations of the blue skies of Mars. I think Don Davis did most of them. Paucity of atmosphere was expected to produce skies that were blue, deep blue, and blue-black. At the time, dust and fogs were not generally considered to be worth considering.

The very first color picture from the surface of Mars showed a blue sky, but it was quickly corrected to pinkify the sky according to the new standards rather suddenly whipped up. Subsequent images showed a pinker and pinker sky, except at sunset when the sky turned blue. Fascinating.

Then, decades later, Viking images were recalibrated. Some of them suddenly revealed a very startling blue sky, others showed an unappetizing green sky. But frequently the corrections showed a white sky near the horizon, becoming bluer the higher the angle of view.

Pink skies, yellow skies and white skies are certainly possible. So are blue skies. There is somewhat less of a prejudice against blue skies on Mars now than there once was, but still the debate "rages."

Don Davis's "Color of Mars" page may help:
http://www.donaldedavis.com/PARTS/MARSCLRS.html

Here's an example of a "blue sky" image from the current crop:

Note that it is very similar to the first color image sent from Mars by Viking 1. However, I make no claim that my image processing is "correct." It is simply one of the many color composites that can be generated from the available data.

But it is apparent in this "blue sky" image that the salt deposits that are so fascinating look to be extruded from below. There's an interesting thought.

How might salt be extruded at the top of a hill?