LRO Spies Lunar Crater Covered in Darkness and Ice


Video courtesy of NASA

CAPE CANAVERAL, Fla – NASA’s Lunar Reconnaissance Orbiter (LRO) was sent to survey the Moon for potential resources that could be used by explorers one day – and has apparently found the most important in abundance – water. Data gleaned from the orbiting spacecraft has pointed to approximately 22 percent of the surface material in a crater at the Moon’s South Pole – being water ice. LRO was launched in June of 2009 from Cape Canaveral Air Force Station’s Space Launch Complex-41 (SLC-41) in Florida.

Scientists at NASA’s Goddard Space Flight Center in Maryland as well as a team from the Massachusetts Institute of Technology, located in Cambridge, have utilized LRO’s laser altimeter to study the floor of Shackleton Crater. The bottom of Shackleton Crater is bright in comparison to the bottoms of neighboring craters. This was the first clue that caused the LRO team to hone in on Shackleton.

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. Image Credit: NASA/Zuber, M.T. et al., Nature, 2012

“The brightness measurements have been puzzling us since two summers ago,” said Gregory Neumann of NASA’s Goddard Space Flight Center in Greenbelt, Md. “While the distribution of brightness was not exactly what we had expected, practically every measurement related to ice and other volatile compounds on the moon is surprising, given the cosmically cold temperatures inside its polar craters.”

Not only does the data from LRO suggest the presence of water ice, a boon for nations with stated plans to travel to the lunar surface, (China, Russia and Japan have announced plans to send astronauts to the Moon) the spacecraft also is helping to explain how craters are formed and to chart the Moon’s unexplored regions.


Video courtesy of NASA

Shackleton Crater was named in honor of Ernest Shackleton who encountered more-than-a-little ice as he explored Antarctica. The crater is about two miles deep and measures some 12 miles across. Due to the Moon’s tilt, Shackleton exists in a world of permanent night and is therefore incredibly cold.

The joint team studying the Moon using LRO published their findings in Thursday’s edition of the journal Nature.

This is an elevation map of Shackleton crater made using LRO Lunar Orbiter Laser Altimeter data. The false colors indicate height, with blue lowest and red/white highest. Image Credit: NASA/Zuber, M.T. et al., Nature, 2012

Using the laser altimeter, LRO mapped Shackleton Crater in detail. The spacecraft also employed this tool to determine how reflective the crater’s surface was (this is known as an object’s albedo). The laser altimeter measured the amount of time it took light reflected off the crater to bounce back. This helped to determine the general elevation of the crater.

“The crater’s interior is extremely rugged,” said Maria Zuber, the team’s lead investigator from the Massachusetts Institute of Technology in Cambridge in Mass. “It would not be easy to crawl around in there.”

One finding initially surprised Zuber and her colleagues. While Shackleton’s floor was bright – the walls of the crater were even brighter. It stands to reason that the floor should be where a majority of the ice is deposited after an impact. Also, while the floor of the crater is never illuminated, the walls of the crater occasionally get a glimpse of the sun. The best explanation that the team could come up with was that “moon-quakes” caused by impact events have caused darker material to be deposited on the floor of the crater, leaving a lighter material to be exposed on the crater’s walls.

“There may be multiple explanations for the observed brightness throughout the crater,” said Zuber. “For example, newer material may be exposed along its walls, while ice may be mixed in with its floor.”

LRO was initially designed and planned to serve as a pathfinder mission for future U.S. missions to the lunar surface. While several other nations have stated their intent to send astronauts to the Moon, the U.S. cancelled a proposed permanent lunar base which would have benefitted from deposits of water ice like the one discovered at Shackleton Crater. The ice can be converted to not just water for drinking and hygiene but for rocket fuel. NASA’s exploration objectives are in transitional state with no clearly-stated objectives as of 2010.

LRO was designed to be a pathfinder mission for future crewed flights to the lunar surface. With those plans scrapped in 2010, LRO is now focused on scientific objectives. Image Credit: NASA/Goddard


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