Why Explore the Moon?
Planetary scientist Ian Crawford presents the case for our return to the Moon.
After a long hiatus following the Apollo missions forty years ago, the scientific exploration of the Moon is undergoing something of a renaissance. In the last few years a flotilla of robotic spacecraft has been sent to orbit the Moon by the space agencies of China, Europe, India, Japan, and the United States. This international concentration of effort is unprecedented in the history of space exploration. In part it reflects a renewed scientific interest in the Moon in its own right, and in part the aspirations of new space-faring nations to demonstrate their growing technical capabilities.
The primary scientific importance of the Moon arises from the fact that it has an extremely ancient surface, mostly older than 3 billion (i.e. 3 thousand million) years, with some areas extending almost all the way back to the origin of the Moon 4.5 billion years ago. It therefore preserves a record of the early geological evolution of a terrestrial planet, which more geologically active bodies, such as Earth, Venus and Mars, have long lost. The ancient lunar surface also preserves a record of everything that has fallen on it throughout the history of the Solar System. This includes fragments of meteorites and comets, as well samples of the ancient solar wind and, possibly, samples of the Earth’s oldest crust, blasted into space by giant meteorite impacts on our planet and collected by the Moon. Taken together, this is potentially a very rich scientific record of Solar System history which, with the possible exception of the much less accessible surface of Mercury, is unlikely to be preserved anywhere else. And it lies only three days away with current spacecraft technology.
The idea that samples of the Earth’s earliest crust might be preserved on the Moon is particularly intriguing. Although we have strong grounds for believing that the Earth, like the rest of the Solar System, is 4.5 billion years old, the oldest actual Earth rocks found to-date are only 3.5 to 3.8 billion years old. All older rocks have been destroyed or buried by Earth’s active geology and climate. The oldest Earth rocks already show tantalising evidence for life having been present on our planet by that early time, but as we don’t have access to any older rocks we cannot be sure exactly how or when life first appeared on our planet. However, as noted above, ancient Earth rocks, blasted into space by meteorite impacts, may be preserved on the Moon. Perversely, therefore, our natural satellite may preserve fragments of Earth’s earliest crust, along with a record of the origin and evolution of life on our planet, which the Earth itself has destroyed. Finding such samples could become a holy grail of future lunar exploration.
The airless surface of the Moon has other scientific advantages as well. It is a superb site for some types of astronomical observation. The lunar far-side, in particular, is probably the best site for radio astronomy anywhere in the inner Solar System, as it is permanently shielded from artificial radio transmissions from Earth, and also shielded from solar radio emissions during the 14-day lunar night. Optical astronomy may also benefit from the establishment of lunar observatories. As the Moon lacks any obscuring atmosphere, the lunar surface is a much better site for astronomical telescopes than the surface of the Earth.
To fully exploit the scientific potential of the Moon, to access the geological record of early Solar System history it undoubtedly contains, and to establish astronomical observatories on its surface, will require us once again to land astronauts on the lunar surface – and this time to stay. This must be the next step in lunar exploration, hopefully in the context of a fully international exploration programme, and science will be a major beneficiary. The Apollo missions demonstrated that human beings are highly efficient as explorers of planetary surfaces, and it is difficult to see how we will ever learn all that the Moon has to teach us about the history of the Solar System, and of our own planet, until people are once again actively exploring its ancient battered surface. Looking to the longer term, the human exploration of the Moon will also help develop essential experience that will be required for the human exploration of other locations in the Solar System, not least the planet Mars which also has much to tell us about the evolution of the Solar System and our place within it.
By helping to identify scientifically interesting places on the Moon, which may be explored when people do eventually return its surface, Moon Zoo participants can make a significant contribution to these exciting future activities.
Ian Crawford is a planetary scientist in the Department of Earth and Planetary Sciences, Birkbeck College London, and a member of the Moon Zoo Science Team.