May 19, 2013 | 04:51 AM (BD Time)
19 May, 2013 Sunday
Nasa’s Grail twins to make gravity maps
Nasa is sending twin probes called Grail to map tiny variations in the pull of gravity around the lunar body. The information should give scientists fresh insight into the internal structure of Earth's satellite.
This will help explain many mysteries, such as why the farside of the Moon looks so different from that of the nearside with its great swathe of dark volcanic plains, or maria.
The data also will be an invaluable navigation tool for future exploration, enabling other spacecraft to make more precise landings.
A Delta rocket sent the Grail twins on their way. Its launch from the Cape Canaveral Air Force Station occurred at 09:08 EDT (13:08 GMT; 14:08 BST).
The journey to the Moon is a slow cruise, however. The duo is not expected to enter into orbit until the turn of the year. Scientists already have some lunar gravity maps. Much of this information was built up by tracking small perturbations in the orbits of previous spacecraft as they circled the Moon. But the maps are very coarse, especially for the farside. "The improvement that Grail will have for the gravity field on the nearside is a factor of 100 better than we have right now, and on the farside it is a factor of 1,000," said Grail programme scientist Dr Robert Fogel.
"Imagine trying to see something microscopic with your own eyes and then putting a lens in front of them that has 100 times power or 1,000 times power - it becomes a different world; and that's what we'll get with Grail," he told BBC News.
Grail is an acronym for Gravity Recovery and Internal Laboratory. Its mission is very similar in design to that of a Nasa/German Space Agency venture called Grace that is currently mapping variations in gravity across the Earth.
These differences are the result of an uneven distribution of mass. Obvious examples at the Moon's surface include big mountain ranges or deep impact basins, but even inside the lunar body the rock will be arranged in an irregular fashion, with some regions being more dense than others.
All this will have a subtle influence on the pull of gravity sensed by over-flying spacecraft.
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