Did You Know

On 7 November 2005, NASA scientists observed an explosion on the Moon. The blast, equal in energy to about 70 kg of TNT, occurred near the edge of Mare Imbrium. The explosion was caused by a 12 cm-wide meteoroid slamming into the surface at about 27 km/s. Unlike Earth, the Moon has no atmosphere to burn meteoroids up, so they hit the ground and explode. The scientists captured the impact on video while observing through a 10-inch telescope. The impact gouged a crater in the Moon's surface about 3 m wide and 0.4 m deep.

In contrast to the dark maria, the light-coloured highlands are elevated regions that make up about 84 per cent of the lunar surface. Some of the highlands are mountains or ridges that are the rims of large basins formed from material uplifted after impacts. One of the highest mountains on the Moon, the Apennines, forms part of the Imbrium basin.

Highland rocks are light anorthosites (feldspars) rich in calcium and aluminium. Many highland rocks brought back to Earth are impact breccias, which are composites of different rocks fused together as a result of meteorite impacts.

Radioactive dating of Moon rocks has shown the mare rocks to be between 3.1 and 3.8 billion years old, while the highland rocks are between 4.0 and 4.3 billion years old.

None of the rocks contains evidence that water once existed on the Moon, and no traces of life have been found.

NASA's Lunar Reconnaissance Orbiter, scheduled to launch in October 2008, will release a probe that will probably crash into the lunar south pole, possibly kicking up a dust cloud that can be tested to see if it includes water vapour. India is also expected to launch a space probe in 2008, carrying a radar instrument that can distinguish between ice and rugged terrain.

Table 6.6 Percentage composition of Moon rocks

Mineral

Mare basalt

Highlands

Whole Moon

Silicon dioxide

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