YM COLUMN

November 18, 2009

A significant amount of water found on moon by LCROSS Mission

There are a number of large craters near the lunar South Pole. The inside of the craters surrounded by sharp cliffs was shadowed in pitch dark for several billions of years because sun lights come only at right angles. One of them is the crater “Cabeus” named after Niccolo Cabeo, a priest as well as philosopher belonging to Italian Jesuit (1586~1650), whose size is 100km in diameter located at latitude 85 degrees south and longitude 36 west.

On October 9, 2009, the rocket “Centaur” of NASA smashed into the crater “Cabeus”, having broken eternal silence over billions of years. Velocity at the time of impact was 9,000km/hour. Centaur weighs 2,200kg. There flied extensively in all directions ejecta plume of gases, fine dusts and heavy fragments of some substance as if like a curtain. It was a solemn blast awoken from stillness in intense cold over billion years.

Telescopes of well-known astronomical observatories and amateur astronomers were waiting in the rising tension for the impact moment 380 thousand kilometers away from earth. According to the calculation in advance, it was expected for the plume to soar up 10 kilometers high. What happened actually was 1.6 kilometers so that none of observations from earth was successful.

In four minutes after the impact, as Centaur plunged toward its own crash, the observatory spacecraft LCROSS was, in descending, collecting scientific data from the flying plume caused by the impact with nine cameras and spectrometers, in which operational process a significant amount of water and moisture vapor were found. The hole in the surface caused by impact was approximately 20 meters in diameter, from where the plume beautifully flied about as wide as 60 to 80 meters; near-infrared spectrometers installed on LCROSS detected water ice and vapor, and ultraviolet spectrometers found hydroxyl (OH) in those plume.

Water volume confirmed to have been contained in plume amounted to 100 kilograms just as much as tens of bucketful. This is fantastic! This much water is only from one impact site, which means to enhance our expectations to produce more and more water as we dig around the surroundings. This is something like excitement over striking crude oil.

Needless to say, discovery of water this time does not necessarily mean that the lunar surface is all covered with moisture like on earth, but at least it means that there exists some amount of moisture as compared to the extremely dry regions on earth. Nevertheless, it is a very significant epoch-making discovery for human dream in exploring and developing moon in the future.

Inside the craters near the lunar South Pole are some corners where sunlights never reach so as to remain in eternal shadow, and so it was presumed from past explorations of moon that there would exist large volume of ice frozen in extreme low temperature. This presumption was based on presence of hydrogen, main component of water, which was discovered by US Lunar Prospector in 1988. In addition to this, Indian lunar explorer Chandrayaan with US made observation instruments onboard and other exploring missions also had found water, a very little amount though. It was only a short while ago when they said, “We may find a spoonful water from a football sized ground.” The greatest achievement this time is that water was found in large quantity.

On top of that, materials other than water were detected in the plume by this LCROSS Lunar Impactor Mission, which means that the impact history of moon from outer world such as comets, asteroids and others has been preserved in frozen conditions of eternal shadow as they had been in original forms. As analysis of the plume materials will proceed from now, the lunar story rich in more variety as to the past history of moon and solar system might be revealed in near future.

Analysis of water will bring forth various information. For instance, sea water of Pacific Ocean and snow falling on North Pole show different assays by isotope analysis, of which methodology analysis will answer our questions if the lunar ice in eternal shadow is origin of comet, or by movement of OH on lunar surface caused by direct hit of solar wind, or somehow of origin of moon itself, or even originated from earth.

I welcome your comments on this column to the following E-mail address.
matogawa@planetary.or.jp

Copyright (c) 2000 The Planetary Society of Japan. All rights reserved

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