After nearly six months of scraping at the polar regions of Mars, NASA's Phoenix lander in 2008 discovered both ice-cemented soil and slabs of pure ice below the surface. It also found that thermal contractions had cracked the ground surface into polygons. Many on the Phoenix team had attributed the cracking to churning of the surface soil layer caused by seasonal frost cycles.
But by comparing geological features from cold, dry regions of Antarctica to those seen in Phoenix photographs, Joseph Levy of Portland State University in Oregon and his colleagues conclude that sublimation of the deeper slab ice is a better explanation for the cracking. The researchers surmise that the Martian landscape has been chiselled more by the steady loss of massive slab ice from below than by frost action in the surface soil.
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Planetary science: Cracking Martian ice. Nature 462, 255 (2009). https://doi.org/10.1038/462255c
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DOI: https://doi.org/10.1038/462255c
