Water Molecules Discovered on the Moon

Distribution of water-rich minerals around a fresh crater.

Image: ISRO/NASA

The data from three separate spacecrafts have found signs of water molecules on the Moon, more than what has been predicted in the past. In addition hydroxyl (OH, in contrast with H₂O, water) has also been found in the lunar soil.

This finding is very surprising because the Moon has long been thought to be a parched and waterless place. Although the moon reaches frigid temperatures in the dark (reaching down to 100K or -173°C), the extreme temperatures in the sunlight were thought to have made the water evaporate completely. The only places immune to this were thought to have been the permanently dark craters at higher latitudes, near the poles of the Moon. However, the new finding suggests that water is much more widespread throughout the Moon.

Chandrayaan-1, ISRO's (Indian Space Research Organization) first mission to the moon, carried with it the Moon Mineralogy Mapper (M3) built by NASA. M3, while in orbit with Chandrayaan-1, used its spectrometer to measure reflected light from the moon's surface in the infrared wavelengths. This allowed the surface composition to be studied in detail. Analyzing the data from the instrument, the M3 team realized that the wavelengths of absorbed light are the same for the absorption patterns for water molecules and hydroxyl.

However, this does not mean that there are large bodies of water, or puddles, on the Moon. The finding only suggests that water and hydroxyl molecules are mixed in and interacting with the rock and dust molecules on the very top surface of the Moon. And M3 also discovered that water, although appearing in different areas throughout the moon, was more prevalent at higher latitudes.

In 1999, the Cassini mission, on a flyby of the Moon while heading towards Saturn, had evidence for water and hydroxyl as well. Cassini's VIMS instrument's data agrees very closely with that from M3. However the findings from Cassini were not published until now.

The Epoxi mission, while on a flyby of the Moon in June 2009 on route to comet Hartley 2 in November 2010, provided further confirmation. It also explored what effect temperature, latitude, composition, and time of day had on the presence of water and hydroxyl.

The finding of water on the Moon is going to be important as it may prove helpful in future human settlements on the Moon. And it is already changing the common perception of the Moon as a completely dry place. What's more surprising is that the rocks collected during NASA's Apollo missions showed signs of water. But those findings were quickly dismissed as the result of contamination by humid air at NASA's Johnson Space Center in Houston, Texas. Now because of this monumental discovery, many are reconsidering the Moon as a very valuable candidate for future human space exploration.

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