
CREDIT: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/National Astronomy and Ionosphere Center, Arecibo Observatory
It has been speculated for some time but yesterday (11/28/2012) it was announced that the evidence is conclusive. The northern polar cap is shielded enough form the sun that temperatures in the shadows are low enough for the maintenance of ice. It is believed the ice and water has accumulated from comet debris and meteorite impacts.