In their gathering of data, scientists need to be careful that they don’t irrevocably pollute the object or area they seek to study. We are particularly concerned about a NASA Moon mission in 2009.

It is fairly common knowledge that the Antarctic and Greenland ice caps are the archives of Earth’s climatic history of the past million years. As the ice formed, it trapped air bubbles. From ice cores drilled today, researchers can use refined analysis techniques to recover information about past atmospheric composition, world temperature, ice extent, winds, volcanic eruptions, and other topics.

In the future, even more advanced techniques will allow the extraction of additional information that is archived in the ice. That discovery will be possible because the drilling of ice cores now does not destroy the ice caps.

In interplanetary space, water molecules have existed for millennia. Dust particles varying greatly in size and composition travel in circumsolar orbits together with molecules of both inorganic and organic material. A small fraction of those objects fall on planetary surfaces, including Earth’s and the Moon’s. Most of those that land on Earth are diluted in the atmosphere, in the oceans, and on the planet’s surface. The search for such extraterrestrial objects here is therefore hopeless, except for a few special cases.

Objects falling on the Moon have a different fate. They are unimpeded by atmosphere, winds, or oceans. Water molecules will be absorbed on the rocky and sandy surface, to be desorbed later by solar radiation. Due to the Moon’s low gravity, the escape velocity of water molecules is low enough to allow a continuous loss into space. With such conditions, one would not expect to find many water molecules on the lunar surface.

Nevertheless, there are exceptions. Molecules hitting inside small craters near the poles may find a good, protected location; there are certainly small spots that solar radiation will never reach. In those spots there may be interplanetary dust particles and organic or inorganic molecules glued together by frozen water, having accumulated possibly since the Moon was first formed. Those tiny spots are an archive of solar-system history.

In October 2009 NASA’s Lunar Crater Observation and Sensing Satellite team carried out a new Moon mission whose main objective was to confirm the presence of water ice in a permanently shadowed crater (www.nasa.gov/mission_pages/LCROSS/main/prelim_water_results.html). Unfortunately, that fascinating research question was addressed by dropping a 2366-kg “bullet” that destroyed the crater and polluted the impact site. We understand that the damage is a small price to pay for science, but we wonder if NASA considered that future generations of scientists might not want to find those explosives in the Moon’s archives.

From the very basic viewpoint of site preservation, NASA’s experiment was quite primitive; it destroyed the historical record in that location. Scientists over the next few hundred years will develop new analysis techniques. They would, we are sure, be glad to find at least part of the natural archive left intact. Subsequent lunar water experiments should be planned as nondestructive site samplings.

WATER IS DISCOVERED ON THE MOON.

WATER IS DISCOVERED ON THE MOON.

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