NASA scientists, trolling through Lunar Prospector data for signs of water on the moon�s surface, found their evidence of ice deposits in a type of fingerprint left by particles traveling through space.
"[The space probe sent back] the kind of data signature one would expect to find if water were present," said a gleeful Alan Binder, chief investigator of the Lunar Prospector.
This signature comes in the form of neutrons, particles that begin their space lives with high energy levels resulting from the collision between cosmic rays and atoms in a planet�s crust. An instrument called a neutron spectrometer tracks the numbers and various types of neutrons by determining their mass and speed. The instrument is located on board the Prospector, which is traveling in a polar orbit 100 kilometers above the moon.
Neutrons that leave the crust and go directly into space as high-energy particles are called fast, or hot, neutrons. Some neutrons collide with other atoms, most of which are much larger and therefore help the particle retain most of its energy level. Scientists call these neutrons warm, or epithermal. Still other neutrons collide with objects that are the same size, which causes the neutron to transfer most or all of its energy. These are called cool, or thermal, neutrons.
In the Lunar Prospector data, scientists noticed a drastic drop in the population of warm neutrons around the moon�s poles. This drop was accompanied by a spike in the number of thermal neutrons, which was the clear indicator of the presence of hydrogen, said Dr. Bruce Barraclough, the architect of the neutron spectrometer and a member of the technical staff at Los Alamos National Laboratory.
Since a hydrogen atom has the same mass as a neutron, scientists concluded that the more cool neutrons there are, the more hydrogen atoms are present. NASA�s scientists believe this hydrogen is most likely water, because that is the most stable form of hydrogen that could exist on the mostly shady, ever-so-cold poles of the moon.
Thursday�s findings give a much clearer answer to the question about the existence of water on the moon than the disputed findings reported from the 1994 mission by the U.S. Department of Defense�s Clementine satellite. The Clementine probed the moon�s surface with radar and generated evidence of water that was disputed by much of the scientific community. "This [mission] wasn�t intended to look for water; they merely did it just to see how well the radar would pick it up," said Binder, who has spent much of his career studying Apollo data and seeking ways to get back to the moon to learn more about its surface.
The water on the moon could be plentiful enough to sustain a human colony or generate fuel for rockets to return to earth, noted Binder. Thursday�s findings have lent fuel to Binder�s fledgling Lunar Research Institute, a privately held company dedicated to developing low-cost missions to the moon and works in partnership with NASA.
Just how much water exists on the moon has yet to be determined. So far, Lunar Prospector can measure up to a depth of five feet into the lunar soil. Data resulting from this search indicates that there could be anywhere from 11 million to 330 million tons of ice at the poles.
Nonetheless, this data is very speculative. Binder said the craft has more work to do to determine the amount of water, the soil composition, and more. Still to come from the US$65 million Lunar Prospector�s mission is a change from a polar path to an elliptical orbit that will alternate among three points: the north and south poles and the equator.
