© NASA/Zuber, M.T. et al., Nature, 2012
Elevation (left) and shaded relief (right) image of Shackleton, a 21-km-diameter (12.5-mile-diameter) permanently shadowed crater adjacent to the lunar south pole. The structure of the crater's interior was revealed by a digital elevation model constructed from over 5 million elevation measurements from the Lunar Orbiter Laser Altimeter.
NASA said its Lunar Reconnaissance Orbiter (LRO) spacecraft has found a crater - dubbed Shackleton -- on the south pole of the moon that may have as much as 22% of its surface covered in ice.
Shackleton, named after the Antarctic explorer Ernest Shackleton, is two miles deep and more than 12 miles wide and because of the Moon's tilt is always in the dark. Using laser light from LRO's laser altimeter NASA said found the crater's floor is brighter than those of other nearby craters, which is consistent with the presence of small amounts of ice. This information will help researchers understand crater formation and study other uncharted areas of the Moon, NASA said.
NASA said the LRO mapped Shackleton crater with unprecedented detail, and the laser light measured to a depth comparable to its wavelength, or about a micron. That represents a millionth of a meter, or less than one ten-thousandth of an inch. The team also used the instrument to map the relief of the crater's terrain based on the time it took for laser light to bounce back from the Moon's surface. The longer it took, the lower the terrain's elevation, NASA said.
NASA said that in addition to the possible evidence of ice, the study of Shackleton revealed a remarkably preserved crater that has remained relatively unscathed since its formation more than three billion years ago. The crater's floor is itself pocked with several small craters, which may have formed as part of the collision that created Shackleton.
Maria Zuber, the team's lead investigator from the Massachusetts Institute of Technology said that while the crater's floor was relatively bright, its walls were even brighter. The finding was at first puzzling because scientists had thought that if ice were anywhere in a crater, it would be on the floor, where no direct sunlight penetrates. The upper walls of Shackleton crater are occasionally illuminated, which could evaporate any ice that accumulates. A theory offered by the team to explain the puzzle is that "moonquakes"-- seismic shaking brought on by meteorite impacts or gravitational tides from Earth -- may have caused Shackleton's walls to slough off older, darker soil, revealing newer, brighter soil underneath. Zuber's team's ultra-high-resolution map provides strong evidence for ice on both the crater's floor and walls.
"There may be multiple explanations for the observed brightness throughout the crater," Zuber said in a statement. "For example, newer material may be exposed along its walls, while ice may be mixed in with its floor."
This is not the first time NASA has found ice on the moon. The space agency's Lunar CRater Observation and Sensing Satellite (LCROSS)
and Lunar Reconnaissance Orbiter which in 2009 slammed into the Moon as part of an experiment to find out what the orb was really made of found an ice-filled a debris plume from the experiment.
NASA said the mission found evidence that the lunar soil within craters is rich in useful materials, and the moon is chemically active and has a water cycle. Scientists also confirmed the water was in the form of mostly pure ice crystals in some places.
In 2010, using data from a NASA radar that flew aboard India's Chandrayaan-1 spacecraft, scientists detected ice deposits near the moon's north pole. NASA's Mini-SAR instrument found more than 40 small craters with water ice. The craters range in size from 1 to 9 miles (2 to15 km) in diameter. Although the total amount of ice depends on its thickness in each crater, it's estimated there could be at least 1.3 trillion pounds (600 million metric tons) of water ice.