Between 08:38:50 UTC and 08:40:23 UTC Opportunity’s Pancam takes three images with narrowband filters in the three basic colors, from which it was possible to derive this extraordinary true-color image of the furrow created by one of Opportunity’s wheels.
In this case, the original images (especially in green and blue) have a high level of “noise” and so I applied a median filter to all three colors to eliminate spurious dots.
The curious aspect is that the sand appears decidedly reddish just below the surface, while the layer exposed to the air turns green!
Obviously, as long as the greenish spots are visible on the surface of a rock (as in the one visible below) it is impossible to determine from a simple photo to what extent such colorations are part of the mineralogical nature of the rock itself or surface “encrustations”. But in this case it is clear that the greenish coloration of the soil affects only the surface layer of the soil itself.
It seems clear to me that in this case the cause of the greenish coloration is to be found in some kind of chemical-physical interaction between the soil and the atmosphere!
RGB HD image processed: https://image.ibb.co/bvKyZH/Oppy_Sol5062.jpg
Original BN images:
Red (735nm with 20nm bandwidth)
08:38:50 UTC
15:10:07 LTST https://mars.nasa.gov/mer/gallery/all/1/p/5062/1P577566823EFFD283P2362L2M1.HTML
Green (535nm with 20nm bandwidth)
08:39:24 UTC
15:10:40 LTST https://mars.nasa.gov/mer/gallery/all/1/p/5062/1P577566857EFFD283P2362L5M1.HTML
Blue (432nm with 32nm Bandwidth)
08:40:23 UTC
15:11:38 LTST https://mars.nasa.gov/mer/gallery/all/1/p/5062/1P577566916EFFD283P2362L7M1.HTML
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