Scientists have expected for a long time that water ice might be found in the permanently shadowed recesses of Mercurian craters, but nobody’s ever actually seen any — until now. In Kadinsky Crater, near the north pole of Mercury, the MESSENGER spacecraft has spotted ice. It was able to photograph the ice because although the crater is permanently shaded, it isn’t in complete darkness; reflected sunlight from the crater rim does dimly illuminate it. It’s still very dark, but it’s enough for MESSENGER’s Wide Angle Camera, with the right camera settings.
Water is turning out to be a bit more ubiquitous than we’d realized, even in the innermost parts of the solar system.