Academic Reading — Test 116

Reading passage

For most of the twentieth century, the Moon was assumed to be utterly dry. The lunar surface is exposed to the harsh radiation of the Sun and has almost no atmosphere to trap moisture, so scientists reasoned that any water would long ago have escaped into space. This view began to change towards the end of the century, when researchers proposed that the floors of certain craters near the lunar poles might never receive direct sunlight. Because the Moon's axis is tilted only very slightly, the Sun always sits low on the horizon at these high latitudes, and the rims of deep craters can cast shadows that endure indefinitely. Within these permanently shadowed regions, temperatures may fall below minus 230 degrees Celsius, cold enough for water ice to remain stable for billions of years. India entered this field of enquiry with Chandrayaan-1, an orbiter launched in 2008 by the Indian Space Research Organisation, known as ISRO. The spacecraft carried a range of instruments, several of which were contributed by other space agencies as part of an international collaboration. Among the most significant was the Moon Mineralogy Mapper, an American instrument designed to study the composition of the surface by measuring the wavelengths of reflected light. As sunlight bounces off lunar soil, water and a closely related compound called hydroxyl absorb particular wavelengths, leaving a recognisable signature in the reflected spectrum. By analysing this signature across wide areas, the instrument detected traces of water and hydroxyl bound to the soil, especially towards the poles. These were not pools or sheets of ice but molecules clinging to mineral grains, yet their presence challenged the old assumption of a bone-dry Moon. Chandrayaan-1 also released a small probe, the Moon Impact Probe, which was deliberately crashed near the south pole. As it descended, the probe took measurements of the thin gases surrounding the Moon and returned data consistent with the presence of water. Meanwhile, a radar instrument aboard the orbiter scanned the interiors of polar craters. Radar is useful because it can probe shadowed ground that optical cameras cannot see, and ice reflects radar waves in a distinctive manner. The combined evidence from these instruments suggested that water ice was not merely a thin coating on sunlit soil but might also be concentrated, in more substantial quantities, within the cold traps of the polar craters. The story did not end with the first mission. In 2019 ISRO launched Chandrayaan-2, which placed a more advanced orbiter around the Moon. Its lander was intended to touch down near the south pole but was lost during its final descent. The orbiter, however, continued to function and carried instruments capable of mapping surface water with greater precision than before. One of these measured the amount of hydrogen near the surface, since hydrogen is a key component of water and its concentration offers an indirect clue to where ice may lie buried. The mission refined earlier maps and confirmed that the southern polar region was a particularly promising place to search for accessible water. In 2023 India achieved a further milestone when Chandrayaan-3 successfully landed near the south pole, becoming the first mission from any nation to set down so close to that part of the Moon. Although its primary purpose was to demonstrate a safe landing and to deploy a small rover, the lander also measured how temperature changed with depth in the upper layer of soil. It found that the surface heated and cooled dramatically, while material only a few centimetres below stayed far cooler. This insulating quality of the lunar soil matters greatly, because ice buried beneath an insulating layer is protected from the heat of the lunar day and is therefore more likely to survive. The practical importance of these findings is considerable. Water ice on the Moon could in principle be melted to provide drinking water, split into oxygen for astronauts to breathe, and separated into hydrogen and oxygen to make rocket fuel. Transporting such supplies from the Earth is extremely expensive, so a local source would transform the economics of long-term exploration. For this reason, the south pole has become a focus of international attention, and several agencies are now planning missions to the same region. The Chandrayaan programme did not, on its own, prove that the Moon holds vast reserves of usable ice, and much remains uncertain about how much water exists and in what form. Nevertheless, the missions transformed a tentative hypothesis into a body of mapped, measurable evidence, and in doing so they helped to redraw the scientific picture of our nearest neighbour in space.