[X] My Assistant

[Nirgal]

among the many new pancams at exploratorium there seem to be interesting
images showing what must be clouds, clearly defined as never seen before
at the Gusev site.

http://qt.exploratorium.edu/mars/spirit/pa...HEP2680L7M1.JPG

Interestingly, those are high-res pancam multi-filter sequences.

Questin for Dan (slinted) refering to our recent discussion about sky color:
would't this be wotrth a try to do interesting sky color composites.
Maybe you could use the brightest pixels
in the clouds as a white point reference ?

[edstrick]

The "almost black sky at zenith" idea for Mars partly derives from a characteristic of the Viking Lander cameras. The extreme upper part of the cameras' field of view was vignietted by the optics, possibly <I don't recall> by the ejectible dust-abrasion cover they had on the cameras. (At least one dust cover was ejected to see if there was any dust accumulation on the optics, with minimal evidence for dust accumulated)

The result was in the top 10 degrees of the field of view, the sky rapidly got darker, going pretty nearly black at the top edge of frames that extended up to the top edge. This fooled at least one astronomical artist to paint Mars with a black sky and a bright horizon.

As noted above, the air may be "thin" in terms of not much gas per cubic foot, but the scale height <rate the atmosphere gets thinner with height> is about the same as on Earth. CO2 has about twice the molecular weight as Nitrogen/Oxygen mix, and would reduce the scale height, but the gravity is about 0.4 <very approx numbers here> of one Earth gravity, and the two approximately cancel.