. ▁Sub lim ation ▁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 ▁pol yg onal ▁ground ▁may ▁indicate ▁where ▁future ▁colon ists ▁can ▁find ▁water ▁ice . ▁ ▁Pattern ed ▁ground ▁forms ▁in ▁a ▁mant le ▁layer , ▁called ▁latitude ▁dependent ▁mant le , ▁that ▁fell ▁from ▁the ▁sky ▁when ▁the ▁climate ▁was ▁different . ▁ ▁, ▁ ▁Complex ▁pol yg onal ▁pattern ed ▁ground ▁ ▁Ex posed ▁Ice ▁She ets ▁ ▁Hi RI SE ▁images ▁taken ▁under ▁the ▁Hi W ish ▁program ▁found ▁tri angular ▁sh aped ▁de press ions ▁in ▁Mil ank ov ic ▁Cr ater ▁that ▁research ers ▁found ▁contain ▁vast ▁amounts ▁of ▁ice ▁that ▁are ▁found ▁under ▁only ▁ 1 – 2 ▁meters ▁of ▁soil . ▁These ▁de press ions ▁contain ▁water ▁ice ▁in ▁the ▁straight ▁wall ▁that ▁faces ▁the ▁pole , ▁according ▁to ▁the ▁study ▁published ▁in ▁the ▁journal ▁Science . ▁ ▁E ight ▁sites ▁were ▁found ▁with ▁Mil ank ov ic ▁Cr ater ▁being ▁the ▁only ▁one ▁in ▁the ▁northern ▁hem is phere . ▁ ▁Research ▁was ▁conducted ▁with ▁instruments ▁on ▁board ▁the ▁Mars ▁Re con na issance ▁Or b iter ▁( M RO ). ▁ ▁The ▁following ▁images ▁are ▁ones ▁referred ▁to ▁in ▁this ▁study ▁of ▁sub sur face ▁ice ▁sheets . ▁ ▁These ▁tri angular ▁de press ions ▁are ▁similar ▁to ▁those ▁in ▁scal loped ▁terrain . ▁▁ ▁However ▁scal loped ▁terrain