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Return to the Moon
Dr Duncan L Copp
June 2008
Return to the moon | Written in the rocks | A grand observatory | Space resource | A manned return? | The driving force | Find out more
Written in the rocks
The moon is like the Rosetta Stone in unravelling 4.5 billion years of solar system history. 'The moon is a linchpin in planetary science,' says Dr Heather. 'It holds within its crust the key to unlocking many geological and astronomical enigmas; a record that has been obliterated on the more active Earth.' The clues remain because, geologically speaking, the moon died very early on in its history. Its surface hasn't undergone the rejuvenating facelifts to which Earth has been subjected. Here, plate tectonics constantly recycles Earth's crust, erasing clues to past events. But the lunar crust is not recycled because the moon does not have the shifting tectonic plates. Consequently, it has preserved within it evidence of the same forces and principles that shaped the whole of the solar system.
Also recorded on the moon are the impacts of asteroids and comets (rubble left over from the creation of the solar system) hitting the surface. The countless craters that pepper the moon's surface tell the story of a debris bombardment rate over time. This information is useful for dating the surface features of the terrestrial planets, in particular Mercury and Mars, whose surfaces have remained relatively unchanged by plate tectonics.
Furthermore, buried within some moon craters (especially those at the lunar poles) are thought to be traces of ice, left behind from icy comet impacts. Locked within this ice are important chemical clues to the proportions of elements present early in the history of the solar system. Analysis of the ice could yield clues to the origins of the building blocks of life.
While the US Apollo astronauts and the Russian sample-return robot missions gave a tantalising insight into how the moon formed, there is still a great deal to understand. Currently, the hottest theory regarding the formation of the moon is that a giant asteroid the size of Mars struck Earth, resulting in a mass of debris being flung out into Earth's orbit which later recombined to form the moon. This was followed by a period of global melting when an ocean of molten magma covered the lunar surface. The magma then chilled to form a chemically distinct crust.
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In the Shadow of the Moon >
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