Hopes for large lakes of frozen water at the Moon鈥檚 poles have taken another bashing, with new images of a prominent crater revealing dull lunar dust instead of shiny pools of ice.
A decade ago, NASA鈥檚 Lunar Prospector spacecraft suggested the Moon鈥檚 poles boast large concentrations of hydrogen near the surface, which could be in the form of frozen water deposited by comets. This would be vital for future colonies on the Moon, providing drinking water for astronauts and hydrogen fuel for their vehicles.
Advertisement
The Shackleton Crater on the south pole had been a prominent candidate for a future base station, since it contains a ledge on its rim that would have been an ideal landing spot.
If the crater also holds frozen water, it would be a perfect location. But that possibility seemed to evaporate when radar signals formerly attributed to water ice were also found to reflect off sunlit areas where ice could not survive.
So researchers had hoped that the Japanese spacecraft , which launched in September 2007, could shed light on the question by peering down on the region from lunar orbit.
Scattered light
The spacecraft contains a highly sensitive camera that can capture images of the Moon鈥檚 surface even in the near-total darkness of its south pole.
The inside of the crater receives no direct sunlight. But for a short period during summertime in the Moon鈥檚 southern hemisphere (November and December in the Earth鈥檚 calendar), a small part of its rim catches a few rays. These are then scattered to the crater floor.
A team led by Junichi Haruyama of the Japan Aerospace Exploration Agency in Kanagawa analysed images of the crater taken on these brighter days. The images were snapped by the spacecraft鈥檚 Terrain Camera, which can resolve objects as small as 10 metres across.
鈥淚t鈥檚 given us access to the poles that we鈥檝e never seen before,鈥� says team member of Brown University in Providence, Rhode Island.
The images provided a full profile of the crater 鈥� including details of tiny craters on its floor and two landslides from the inner wall.
Dull soil
But according to Pieters, the most striking feature was what was missing. 鈥淚f there had been nice, clean ice, we鈥檇 have seen brighter reflections from its surface 鈥� but none were visible,鈥� she told New 杏吧原创. Instead, the images just revealed dull lunar soil.
This doesn鈥檛 completely rule out the possibility of frozen water within the crater, she points out 鈥� it could be buried, or the ice crystals could be dirty and mixed with particles of soil. Alternatively, there may be no water at all, and the hydrogen could be trapped in another compound like methane.
Ice particles trapped within the lunar soil could still be useful for a human base station, but this would depend on the cost of mining the ice and extracting the water, says , an astronomer at Cambridge University.
鈥淭he key is the relative cost of all that mining against shipping up liquid water from Earth,鈥� he told New 杏吧原创. 鈥淭his result shows it鈥檚 not going to be easy.鈥�
But Alan Smith, director of the Mullard Space Science Laboratory at University College London, disagrees: 鈥淚f [water ice] is present at levels of just a few percent, it could be very useful for future missions. In fact, small crystals within a sandy mixture may be even easier to process.鈥�
Journal reference: (DOI: 10.1126/science.1164020)
