Today's Image of Mars shows scallops (pits open on one side) and boulders in Utopia Planitia. The 3D high resolution anaglyph shows polygon features that develop as a result of temperature changes that cause ice contraction and expansion.
There are also numerous boulders that measure approximately 1 meter in diameter. Scientists know they are boulders and not ice because ice cannot remain stable on the Martian surface.
It is speculated that at least ten meters of ice has sublimated from some places in this image, which has created the pits and other features we see in this image. But how did the ice get there in the first place? Mars once had a wetter, warmer environment, but over billions of years Mars became much colder and the water that once covered the surface froze or retreated underground.
Clicking on this image will take you to the original captioned image from HiRISE.