The continuous shadows in the south polar craters cause the floors of these formations to maintain a temperature that never exceeds about 100 K. For Shackleton , the average temperature was determined to be about 90 K , reaching 88 K at the crater floor . Under these conditions , the estimated rate of loss from any ice in the interior would be 10 − 26 to 10 − 27 m / s . Any water vapor that arrives here following a cometary impact on the Moon would lie permanently frozen on or below the surface . However , the surface albedo of the crater floor matches the lunar far @-@ side , suggesting that there is no exposed surface ice .