Caroline Morley, online picture researcher
New map of Shackleton crater false-coloured to emphasise height (Image: NASA/M.?T. Zuber and colleagues, Nature, 2012)
The four words "Shackleton", "ice" and "south pole" often occur together. On one of his expeditions, Antarctic explorer Ernest Shackleton's ship Endurance became trapped in pack ice. Against all odds, all his men survived, and Shackleton is remembered as a heroic leader for the decisions he made under pressure.
Those same four words are perhaps a little more surprising when we add "moon" and "crater" to them. NASA has announced that its Lunar Reconnaissance Orbiter (LRO) has returned measurements that indicate ice on the surface in the Shackleton crater at the moon's south pole.
The crater is over 19 kilometres wide and 3 kilometres deep, and is thought to have been created more than 3 billion years ago. The lunar south pole is in permanent sunshine because of the moon's tilt, but Shackleton's interior is permanently shaded by its own walls. The LRO's laser altimeter mapped the dark crater floor (as seen in this image) and also measured the brightness of reflections from its surface. From the brightness readings, it looks like up to 22 per cent of the crater's surface could be covered in ice, mostly in the walls. Other craters in the region appear to be much drier.
The combination of permanent sunshine for energy and the possible presence of a water resource have led NASA to suggest that the moon's south pole could be a contender for human settlement. So one day we might also be able to add "explorers" to the words that fit with "Shackleton, ice and south pole" on both Earth and the moon.
Journal reference: Nature, DOI: 10.1038/nature11216
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