A split image of Shackleton crater showing elevation on the left and a normal… (NASA/Zuber, M.T. et al.,…)
NASA's Lunar Reconnaissance Orbiter spacecraft has found that the Shackleton crater at the moon's frigid south pole contains about 22% ice on its surface, astronomers reported Thursday in the journal Nature. To their surprise, the team apparently saw more ice on the walls of the crater than on its floor. Such ice could prove very valuable for any extended moon mission, providing water and a potential fuel source to astronauts.
The Lunar Reconnaissance Orbiter, known as LRO, was launched in June 2009 to prepare a detailed map of the moon's surface. Having achieved that objective, the craft is now carrying out science experiments, such as determining what causes an unusual brightness in the Shackleton crater. "The brightness measurements have been puzzling us since two summers ago," said Gregory Neumann of NASA's Goddard Space Flight Center in Greenbelt, Md.
Shackleton crater, named for Antarctic explorer Ernest Shackleton, is two miles deep and more than 12 miles wide. Because it is so close to the south pole, sunlight never reaches the floor of the crater, although it occasionally shines on the walls. Using LRO's laser altimeter, a team headed by Maria Zuber of MIT measured the reflectivity of the floor and walls of the crater. The laser beam penetrates the surface to a depth corresponding to its wavelength, which is less than one ten-thousandth of an inch.
The floor of the crater was brighter than expected, indicating the presence of the ice. But the walls were even brighter, which is unexpected because their occasional exposure to sunlight should cause the ice to sublime. The team speculated that occasional moonquakes -- seismic shaking brought on by meteor impacts or gravitational tides from Earth -- may cause the crater walls to slough off older, darker soil, revealing newer, brighter soil underneath.
A video of the crater is available here.