[meteorite-list] LRO Reveals Ice Content in Moon Crater

[Ron Baalke]

June 20, 2012

Dwayne Brown 
Headquarters, Washington 
202-358-1726 
dwayne.c.brown at nasa.gov 

Nancy Neal-Jones / Bill Steigerwald 
NASA Goddard Space Flight Center, Greenbelt, Md. 
301-286-0039 / 301-286-5017 
nancy.n.jones at nasa.gov / william.a.steigerwald at nasa.gov 

RELEASE: 12-208

NASA SPACECRAFT REVEALS ICE CONTENT IN MOON CRATER

WASHINGTON -- NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft has 
returned data that indicate ice may make up as much as 22 percent of 
the surface material in a crater located on the moon's south pole. 

The team of NASA and university scientists using laser light from 
LRO's laser altimeter examined the floor of Shackleton crater. They 
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. The findings 
are published in Thursday's edition of the journal Nature. 

"The brightness measurements have been puzzling us since two summers 
ago," said Gregory Neumann of NASA's Goddard Space Flight Center in 
Greenbelt, Md., a co-author on the paper. "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." 

The spacecraft mapped Shackleton crater with unprecedented detail, 
using a laser to illuminate the crater's interior and measure its 
albedo or natural reflectance. The laser light measures 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. 

In addition to the possible evidence of ice, the group's map 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. 

The crater, named after the Antarctic explorer Ernest Shackleton, is 
two miles deep and more than 12 miles wide. Like several craters at 
the moon's south pole, the small tilt of the lunar spin axis means 
Shackleton crater's interior is permanently dark and therefore 
extremely cold. 

"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." 

While the crater's floor was relatively bright, Zuber and her 
colleagues observed that its walls were even brighter. The finding 
was at first puzzling. 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," said Zuber. "For example, newer material may 
be exposed along its walls, while ice may be mixed in with its 
floor." 

The initial primary objective of LRO was to conduct investigations 
that prepare for future lunar exploration. Launched in June 2009, LRO 
completed its primary exploration mission and is now in its primary 
science mission. LRO was built and is managed by Goddard. This 
research was supported by NASA's Human Exploration and Operations 
Mission Directorate and Science Mission Directorate at the agency's 
headquarters in Washington. 

For an image of the crater, visit: 

http://go.nasa.gov/MlzloW 

For more information about NASA's Lunar Reconnaissance Orbiter 
mission, visit: 

http://www.nasa.gov/lro 
	
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