Competitive Exams: Current Affairs 2012: GRAIL Spacecraft

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Probes have mapped in great detail the Moon's surface and the minerals to be found there. India's Chandrayaan-1 and other spacecraft found unmistakeable signs of water. The Apollo astronauts as well as the Soviet Union's unmanned landers brought back rock and soil samples that could be carefully studied in the laboratory.

Despite half a century of lunar exploration with automated probes and the efforts of a dozen men who walked its surface, the

Moon has lost little of its allure, especially for scientists. The twin spacecraft of the Gravity Recovery And Interior Laboratory (GRAIL) mission despatched by the U. S. National Aeronautics and Space Administration are the latest to go there. In recent days, they slipped into lunar orbit after taking a circuitous, low-energy passage from Earth that lasted three-and-a-half months.

The GRAIL spacecraft are expected to provide important clues to what the Moon is like deep inside by mapping variations in its gravitational field with much higher resolution than before:

When the science phase of the mission starts in March 2012, the two satellites will be flying in formation, one behind the other, at a height of about 55 km. The spacecraft will then transmit GPS-like radio signals so that the distance between them can be accurately measured. That gap changes as they fly over areas with greater or lesser gravity. Scientists will then need to take the data and combine them with other information, such as topographical maps prepared with data from other satellites, in order to try and figure out the structure of the Moon's interior and its composition.

Such analysis can provide insights into many aspects of Earth's natural satellite. Why, for instance, are the two hemispheres of the

Moon so different from each another? The side we see is flat with lava-filled basins that appear as dark patches. The farside, on the other hand, is mountainous and has a much thicker crust.

One explanation for this asymmetry, based on computer simulations and published recently in a scientific journal, suggested that the Moon once had a smaller companion that subsequently crashed into it. The GRAIL data could help substantiate or rule out such a scenario. Likewise, getting a handle on the distribution of materials in the interior will be invaluable in understanding the

Moon's evolution. As always, such quests of scientific discovery can reveal the unexpected.

Courtesy: The Hindu

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