Dark Spots as indicators

There were some targets imaged by the older MOC that showed some dark spots that only showed darker albedo. These seemed to be in some of the regions that are suggested to be target areas where plumes occur. Methane or clathrates of methane were speculated, but a definite methane signal was not agreed upon by a majority at the time the images were shot.

Some potential CRISM targets to look for chemical change

In Syrtis Major: http://www.msss.com/moc_gallery/e13_.../E1800771.html

http://www.msss.com/moc_gallery/e13_.../E1600350.html

http://www.msss.com/moc_gallery/e13_.../E1300145.html

From Arabia:

http://www.msss.com/moc_gallery/e13_.../E1600823.html

http://www.msss.com/moc_gallery/e13_.../E1401758.html

http://www.msss.com/moc_gallery/e13_.../E1800981.html

From Terra Sabaea:
http://www.msss.com/moc_gallery/e13_.../E1302274.html

http://www.msss.com/moc_gallery/e13_.../E1700363.html

http://www.msss.com/moc_gallery/e13_.../E1701888.html

There may be a number of different viable explanations for the albedo contrasts. But CRISM could further sort out, by performing a mineral analysis, if a chemical alteration that involved methane destruction along the way could be possibly responsible for some of the albedo contrasts.