Polygonal, patterned ground is quite common in some regions of Mars.
 It is commonly believed to be caused by the sublimation of ice from the ground.
Sublimation is the direct change of solid ice to a gas.
 This is similar to what happens to dry ice on the Earth.
 Places on Mars that display polygonal ground may indicate where future colonists can find water ice.
 Patterned ground forms in a mantle layer, called latitude dependent mantle, that fell from the sky when the climate was different.
Polygonal, patterned ground is quite common in some regions of Mars.  It is commonly believed to be caused by the sublimation of ice from the ground. Sublimation is the direct change of solid ice to a gas.  This is similar to what happens to dry ice on the Earth.  Places on Mars that display polygonal ground may indicate where future colonists can find water ice.  Patterned ground forms in a mantle layer, called latitude dependent mantle, that fell from the sky when the climate was different.
Ismenius Lacus quadrangle