Tikalon Blog by Dev Gualtieri

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Lunar Water

June 4, 2012

Music changed abruptly in my teen years . Radio play in the early 1960s was mostly ballads , show tunes ; and quite a few novelty records , such as "Itsy Bitsy Teeny Weeny Yellow Polka Dot Bikini ."[1] Then came the British Invasion , and America's response.

I was a Top-40 DJ at a small 1,000 watt AM radio station at the end of the British Invasion. This is a somewhat lesser pedigree than that of Ted Baxter of The Mary Tyler Moore Show , who worked at a "five thousand watt radio station in Fresno, California ."

The song, Moon River (music by Henry Mancini , lyrics by Johnny Mercer ) was introduced in the 1961 film , Breakfast at Tiffany's .[2-3] It won the 1961 Academy Award for Best Original Song , the 1962 Grammy Award for Record of the Year , and it's best known as the theme song for Andy Williams .

There are so many places on Earth named "Moon" that we never take a phrase like "moon river" literally . Finding a river on the Moon is more unlikely than finding one on Mars , so the Selenites must be using water wells . There's the possibility, however, that there was water in the primordial Moon, and some water may still exist there, as ice , or trapped in minerals .

Figure caption

With the orange cast, it may look like Mars , but this is a photograph of the Moon during the November 9, 2003, lunar eclipse .

(Photo by Oliver Stein, via Wikimedia Commons).

I wrote about the search for water on the Moon in a previous article (New Moon, October 25, 2010). Lunar water would make exploration and habitation of the Moon a lot easier, since humans require a lot of water to survive. Free water is absent from the Moon's surface, since the Moon's gravity is too small to retain any gases , and any liquid water would have evaporated into space.

As pointed out in two early papers by Kenneth Watson , Bruce C. Murray , and Harrison Brown of Caltech , the rate of gravitational escape of water molecules is small enough that water vapor could collect as ice in areas of polar craters that are perpetually shadowed from the Sun .[4-5] Their numerical calculations, in the age before rapid computation, showed that the amount of water lost from the Moon in its present condition would have been just a few grams per square centimeter of surface area.[5]

In 2010, NASA tested this hypothesis by a controlled 5,500 mile/hour impact of the Lunar Crater Observation and Sensing Satellite (LCROSS), and its associated Centaur rocket, into the Cabeus crater on the Moon.[6-8] Cabeus is in the Moon's southern polar region, and its walls have protected some portions of the lunar terrain from sunlight for billions of years. The temperature in these regions is about 40 K .

The impact ejected a plume of lunar material nearly ten miles high, and instruments on LCROSS and the Lunar Reconnaissance Orbiter (LRO) detected water ice . The data indicate that Cabeus may contain a billion gallons of water, but this amounts to just twice the water density of the Sahara desert . The plume itself contained about 41 gallons of water, mixed with quite a few chemicals .[8]

US stamp of first man on the Moon

Appropriately, an air mail stamp .

I'm sure Neil Armstrong's boots weren't a protection from getting his feet wet.

(Via Wikimedia Commons).

Arlin Crotts of Columbia University's department of Astronomy and Astrophysics has just published three articles on the arXiv preprint server that review the historical record of observations relating to the existence of water on the Moon.[9-11] These articles collect the available information on lunar water into one convenient record.

Crotts writes that Harold Urey , Nobel Laureate in chemistry for his discovery of deuterium , was a proponent of lunar water.[9] Urey's idea that water can exist on the Moon was not well accepted, and he even wrote that some of his opponents thought that his idea was the product of too much vodka .[12]

The Moon's regolith (the loose surface layer), is somewhat impervious to water. A water molecule traveling from just below this layer would have a trillion collisions with particles before reaching the surface. If such molecules have even a small residence time on the surface of particles, this will add up to times on a geological scale .[10] Water deep within the Moon would explain deep quakes , which are facilitated by water on Earth.[10]

Crotts writes about the interesting events called "transient lunar phenomena ," or TLPs, which are the transient changes in the Moon's appearance. Some, of course, are due to asteroid impacts , but others may arise from gas release. The figure below shows the large extent of these TLPs.

Locations of transient lunar phenomena

Locations of transient lunar phenomena (TLPs).

The size of the circles represents the number of reports. (1) 46.7% Aristarchus /Schroter's Valley (2) 15.6% Plato .

Moon image is NASA Galileo PIA00405.

(Modified image, via arXiv Preprint Server).[11]

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