A new chapter has been added to the decades-long scientific quest for water on the moon. An instrument on the Chandrayaan-1, known as the Moon Mineralogy Mapper, has detected unmistakeable signs of water molecules at many places on the surface of our celestial neighbour. Years before humans set foot on the moon, scientists conjectured that there might be water there. But when samples of lunar rock and soil brought back by the Apollo astronauts were analysed, the results dampened such hopes. The moon appeared to be, in the words of one scientific paper, “an exceedingly dry place.” The search for water on the moon, however, revived in the 1990s when two U.S. spacecraft, the Clementine and the Lunar Prospector, found evidence for what was said to be water in the form of ice in permanently shadowed craters at the poles. But this evidence has been hotly contested. So much so that last year Japanese researchers declared that careful analysis of images taken by the Kaguya/SELENE spacecraft did not throw up any sign of ice inside a key crater at the south pole. But it was also last year that U.S. scientists published a study that used new techniques to examine beads of volcanic glass collected by two Apollo missions. They found minute traces of water. That suggested that water had been a part of the moon since its formation and could be found deep inside it.

Against this background, the discovery of traces of water by the Chandrayaan-1, supported by findings from two U.S. deep space missions that gazed at the moon as they passed by, is of huge scientific interest. Scientists have long speculated that solar wind, carrying charged particles from the sun, could interact with the lunar soil to produce water. Now evidence from Chandrayaan-1 and the other two spacecraft indicates that such a process is likely to be at play on the moon. Water, it would seem, is being constantly generated all over the lunar surface. Much of it may well boil off into space; some of it may percolate deeper down into the soil. Some of the water could end up at the bottom of deep polar craters, which have recently been described as some of the coldest places in the entire solar system. Such water, it is said, will benefit any future efforts to establish a manned outpost on the moon, supplying drinking water and rocket fuel. The day when such a need might arise seems very far off indeed. It is not even clear when humans might next go to the moon, let alone set up bases there. For the present, it is science that profits most from the Chandrayaan-1’s discovery of water. Missions of space exploration should not be judged by any immediate returns they produce. The excitement over such voyages is a testament to our desire to better understand the world around us and the universe beyond.

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