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NASA spacecraft finds possible evidence of ice content in moon crater | Data from NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft has indicated that 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 brightness measurements have
been puzzling us since two summers ago. 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,” said Gregory Neumann of NASA’s Goddard
Space Flight Center in Greenbelt, Md., a co-author on the paper. 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. It would
not be easy to crawl around in there,” said Maria Zuber, the team’s lead investigator
from the Massachusetts Institute of Technology in Cambridge in Mass. 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. For example, newer material may be exposed along
its walls, while ice may be mixed in with its floor,” said Zuber. The findings
have been published in the latest edition of the journal Nature.
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