I showed the raw image to a few geologists who said the image just showed a lot of dust devil activity. Sure there were dust devils there, but the terrain definitely showed deep shadows from the cracks.

If the cracks were indicative of water ice, this would mean there is an enormous resource for life on Mars as well as a source of water for any future human missions to Mars.

Not wanting to just dismiss the cracks and crevices as merely dust devil activity I asked circadian astrobiologist Dr. Joseph Miller of the University of Southern California to do some computer enhancements for me from this same latitude. His image (pictured) dramatically shows the extended relief of the topography.

Miller's enhanced image show that the cracks are not just dust devil tracks as others have interpreted but are rather genuine cracks and crevices on the surface with some dust devil tracks running through and over them.

These first few images piqued my curiosity, so I continued to look at other MGS frames from this latitude and found similar features in an enormous area that almost covers the entire northern hemisphere between 50 and 65 degrees.

Most of the images from MGS at these latitudes reveal numerous cracks, crevices, and fissures with abundant partially buried craters poking up through.

In most of images I examined numerous dust devil tracks are seen crisscrossing the terrain making it somewhat confusing to sort out which were true cracks and what were dust devil tracks.

Along with cracks and crevices some other images from this region show polygonal terrain, suggestive of the freeze-thaw cycling of ground ice.

This Mars Global Surveyor Mars Orbiter Camera picture shows a pattern of polygons on the floor of a northern plains impact crater. These landforms are common on crater floors at high latitudes on Mars. Full size image

Looking at a good global map of Mars one can clearly see the areas in question – I call it collectively "the dark collar of Mars". This "collar" takes up vast regions in Cebrenia, Casius, Ismenius Lacus, Mare Acidalium, Arcadia and Diacria.

In 2001 planetary geologists Kathryn Fishbaugh, James Head and David Marchant outlined evidence for a glacial retreat of the north polar cap, including evidence of glacial moraines, sedimentation at the margins, and drainage channels they found associated within the Olympia Depression.

The researchers cited that the retreat of the polar cap had likely occurred in recent geological time during the Late Amazonian. However, I did not read mention by them of the evidence for glacial ice contained in the dark collar. The most recent scientific reports focus on the potential of regions on Mars that may show evidence for subsurface frozen lakes or oceans.

However, I wondered if the "dark collar" in the northern hemisphere was perhaps the largest single piece of evidence for an ancient retreating glacier from the previous ice age.

An artist's interpretation like this one from NASA/JPL/Brown University shows the extant of the last Martian ice age. Where did all that ice go? Or is it still there? Full size image

If remnants of the Late Amazonian glacier were indeed located within the dark collar, a layer of volcanic ash, impact debris and dust perhaps no more than a few hundred meters thick would have covered it.

It would be just thick enough so that it would prevent the ice beneath from being directly observed. The debris lying on top of the glacier would also thermally protect the ice from summertime sublimation. By comparing features found in the dark collar area to the light-toned plains just below, several immediate distinctions can be made.

1) Few cracks, crevices, or partially buried craters are seen in the lighter plains areas.

2) The ratio of dust devil tracks in the dark collar areas are on the order of many magnitudes greater than those in the light toned areas.

3) The cracks, fissures, crevices and partially buried craters appear to abruptly stop when you get to about 67 degrees north latitude.

If the dark collar is the remnant of a an ancient receding glacier, then why does it only occur between 50 - 65 degrees North? Why did it not continue all the way up to the polar ice cap?

Looking at a map between 67 degrees north latitude and where the dark polar ice cap deposits begins, the terrain is comprised mainly of a lighter-toned surface material where few, if any cracks, crevices, moraines, or other features that are found in the dark collar can be seen.

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