It is not just that the Chandrayaan-1 has found water on the moon. The bigger question is how that water might have been produced and where it could have accumulated.

The water could come from different sources. Countless comets and meteors that have crashed into the moon over billions of years might have brought water. Last year, researchers published a paper in Nature about water contained in tiny beads of lunar volcanic glasses that were collected by two Apollo missions. The discovery suggested that water might exist deep inside the moon.

Now the Chandrayaan-1 data provides support for the idea that solar wind, made up mostly of hydrogen ions, interacts with oxygen in the lunar soil and rocks to produce water. When hydrogen and oxygen atoms bond, hydroxyl is generated; addition of one more hydrogen atom results in water.

Much of that water may be lost to space but some of it could be transported along the surface till it becomes trapped at the bottom of icy cold polar craters that are never exposed to sunlight. “If the water molecules are as mobile as we think they are — even a fraction of them — they provide a mechanism for getting water to those permanently shadowed craters,” observed Dr. Carle Pieters of Brown University in the U.S, principal investigator for the Moon Mineralogy Mapper (M3) on the Chandrayaan-1.

Water ice

Two U.S. spacecraft that travelled to the moon in the 1990s found indications that there was indeed water ice at the bottom of polar craters, but the evidence is disputed. The radars on the Chandrayaan-1 and the U.S. Lunar Reconnaissance Orbiter (LRO), which is now circling the Moon, may shed new light on this issue.

In addition, the U.S. plans to send the heavy upper stage of a rocket as well as a shepherding spacecraft hurtling into a crater at the Moon’s south pole on October 9. By analysing the debris that is thrown up into sunlight, scientists hope to find signs of any water that might lurk there.

Besides, the M3, which depends on reflected light, can pick up signals for water and hydroxyl from just the top few millimetres of the soil. Whether water has percolated deeper into the soil is not known. Here too the radars on the Chandrayaan-1 and the LRO could help.

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