Originally posted by MrPenny
Why do they only appear at the very crest of a dune? Admittedly, a relatively short lived geological feature. The colorized images posted make it much clearer....something running down the side of a dune.
This is one of the things I'm having a problem understanding. I'm glad you are participating in this thread MrPenny, because you seem to have a good grasp on these things, and your analysis is always rational and persuasive.
They do always seem to appear at the very crest of a dune.
That to me is very strange, both for the 'tree' theory, and for the 'geyser' theory.
The colorized images in my viewing still seem to be showing a 3-D object, however, for the sake of argument, lets say that perhaps these are pictures of sand with water stains running down the sides...
How did the water escape at the top of a sand dune? Where is the water coming from? What is the ejection mechanism? Where does the water go?
I really am trying to understand this explanation, however it's very difficult for me to rationalize a water geyser exploding out of a desert. It's also difficult for me to rationalize the way several of these 'geysers' are all erupting at once. I'm also having a hard time understanding why the water doesn't all gather into a larger aquifer and eject in a manner we've observed on other planetary bodies. Enceleadus is a good example, as are water jets on Earth.
Also, the fact that the 'objects/stains/geysers/trees' only appear seasonally does not necessarily preclude any of these explanations from being correct. All of these phenomenon would be expected to portray seasonal variance (especially in an environment like mars, where temperature varies considerably)
Originally posted by MrPenny
Shadows are out of the question....they are running the wrong direction.
I would agree if your interpretation of the image places the highest height value at the peak of the dune. To my eye this is not the case. In fact, the peak of the dune seems obscured, and the darkest part of the 'object' in question is at the lower right portion of the object. This is what I'm calling 'shadow', as it would appear from the albedo (brightness) to be darker than the portion of the object that appears 3-dimensional.
Perhaps that explains what I'm seeing in a better way?
A side view shot of this area would settle this question in my view...
I'm guessing the rovers aren't near this location, but perhaps there is another way to find the answer. If we can find further imagery from MGS with the Sun at a different angle, we could compare/contrast the images to determine what is shadow and what is not...
I'd love to hear your thoughts on this MrPenny, perhaps I'm just not grasping what appears in these images correctly?
-WFA
) was 'which part of the object is the
"shadow"?' 
. It's funny how people act like english is the only language people speak in the world.
