SciTech

Evidence proves presence of water on moon

Above is an image of NASA’s Lunar Crater Observation and Sensing Satellite(LCROSS). LCROSS will help find water trapped in craters on the moon.  (credit: Courtesy of www.nasa.gov) Above is an image of NASA’s Lunar Crater Observation and Sensing Satellite(LCROSS). LCROSS will help find water trapped in craters on the moon. (credit: Courtesy of www.nasa.gov)

After much debate and with some degree of disbelief, scientists have announced in Science that they have conclusive proof that there is water on the moon. While the current findings speak of minuscule amounts, the authors are cautiously optimistic that more will be found on succeeding missions.

The actual discovery was made by the Moon Mineralogy Mapper, or M3, built and operated by the National Aeronautics and Space Administration (NASA). The M3 was fitted on the Chandrayaan-1 lunar probe launched and operated by the Indian Space Research Organization (ISRO). Many of the scientists involved were suspicious of the results and sought corroboratory data, which they found in the information collected by NASA’s Deep Impact (2005) and Cassini (1997) missions. These two missions had previously directed sensors similar to the M3 toward the moon. However, their findings had not been fully analyzed due to the fact that their primary missions did not involve the moon. They had merely used the moon to configure their sensors. The data was further corroborated by NASA’s Lunar Reconnaissance Orbiter (2009 and still active). Indeed, rocks brought back to Earth by the Apollo missions had also shown evidence of water, but this was written off as contamination by the humid Houston air.

According to an interview with one of the co-authors of the paper, Lawrence Taylor, director of the Planetary Geosciences Institute at the University of Tennessee at Knoxville, the most popular hypothesis for the formation of water is that it is “due to the reaction of solar wind protons with a highly reactive soil.” The moon is subjected to intense ultraviolet radiation and other influences, which cause the particles in its soil to become highly unstable and reactive.
This is because the radiation breaks the bonds between atoms in the molecules. Many of these unstable particles are oxygen atoms. When an atom attached to another atom is knocked away by ultraviolet radiation, it leaves a sort of void which renders the remaining atom unstable.

These voids are what Taylor calls “dangling bonds,” which need particles like protons to stabilize them. The sun ejects a constant stream of such protons (the solar wind), some of which are captured by the lunar soil, forming OH and H2O molecules. According to Taylor, “When sunlight hits a substance, it reflects certain wavelengths which are signatures of its composition.” The M3 was looking for the signature associated with OH and H2O with a device called a reflecting spectrometer, which measures wavelengths that are just a bit longer than those that are visible to us.

Comets, often called “dirty icebergs,” may also be a possible contributor to water resources. They occasionally strike the moon and may leave significant deposits of water when they do.

One important thing to note is that the distribution of water changes constantly as it evaporates — the moon has no atmosphere, and water can evaporate at the extremely low temperatures found there. This evaporation is much more pronounced closer to the equator, where there is more sunlight and higher temperatures. Less water was found in the equatorial regions than closer to the poles.

The authors theorize that much of the water accumulates in regions that Taylor calls “cold traps,” permanently shadowed craters where evaporation is less likely to occur and where temperatures never rise above -380 degrees Fahrenheit. As Taylor explains, “Sit down with a glass of iced tea in front of you, wait about two minutes, and you’ll see it starts to perspire. It’s gathering moisture out of the air.” This is an example of a cold trap, a region that is colder than its surroundings, attracting and collecting moisture. These may provide usable sources of water for future lunar missions.

Serendipitously, NASA actually has a mission in progress to find water in such “cold traps.” Called LCROSS (Lunar Crater Observation and Sensing Satellite), it will — at around 7:30 a.m., Oct. 9 — launch its own spent rocket engine at a crater in order to generate a plume of debris. If there is indeed water ice present in the shadowed areas of the crater, the plume could be as high as 70 kilometers. The probe itself will then fly through the plume and see if it can find any evidence of water. Spectroscopes and telescopes on Earth will also be directed toward the plume.

While the authors of the paper are certain that there is water, they are not yet sure if it is actually usable and are being cautious as to the ways in which the water might be employed. It is easy to see, however, that if the water is usable, it would make a big difference for NASA’s plan to build a base on the moon (to be set up by 2024, according to National Geographic). With the presence of water, oxygen and fuel in the form of hydrogen would be available, simplifying the process and reducing the amount of both elements that will have to be carried there.

The discovery of water on the moon is significant not just because of the technical skill involved or the direct results, but also because it implies greater possibilities and allows humanity to hope that the moon is not as harsh a mistress as she seems.