I'll also note the THEMIS image in the OP is a shaded relief map, intended to show topography and is devoid of surface reflectance in any spectrum.

The Viking mosaic apparently shows surface reflectance in some visible or near visible wavelength, though the link in the OP to the image lacks any attributes. It also appears to have a severe histogram stretch, significant compression artifacts and image seam-lines.

There are better quality Viking images, that are map projected that one could possible compare MGS or Odyssey data to - though I would still be cautious without the raw and ancillary data to do a proper change detection.

You can bet that scientists both inside and outside of NASA are doing these sort of change detection analyses. I defer to their judgement.

CJSF

__________________
Two years ago moved from my town
I was looking up past the city lights
But the city lights got in my way

See the constellation ride across the sky
No cigar, no lady on his arm
Just a guy made of dots and lines

-from "See The Constellation"
by They Might Be Giants