Why did NASA crash a craft into the moon?
The crash was carefully targeted to one of the regions on the Moon where scientists believe there may be large deposits of water, in the form of ice, just below the surface. These special regions are all in craters at high latitudes, near the poles, where they are permanently shaded from the Sun by the crater walls.
The Moon has virtually no atmosphere, so permanently shaded regions are exposed to cold space and have very low temperatures, less than minus 200 degrees Centigrade. At such low temperatures, any traces of water vapour exhaling from the interior of the Moon, or falling onto it as meteors or small comets, can remain trapped for billions of years.
We know that the Moon used to be volcanically active, and that icy grains do fall onto its surface (and onto all of the planets, including Earth) from space, so this is a plausible scenario. The experiment was designed to find out if it is actually what happened.
How can this prove whether there is water on the moon?
The impact generates heat that vaporises any water that is present and throws it up in a plume that can be observed with instruments on spacecraft orbiting the Moon, including spectrometers that can distinguish water from other materials. The Lunar Reconnaissance Orbiter was placed in a low, polar orbit around the Moon by NASA a few months ago specifically for this purpose.(Incidentally, one of the instruments carried on the Reconnaissance Orbiter was designed and built partly at Oxford. Our device, Lunar Diviner, uses infrared radiometry to map the temperature of the Moon’s surface, including the permanently shaded craters and the crash site.) The plume was big enough to be observable through telescopes from the Earth as well, although obviously that is more difficult and did not deliver such good results.
Why do we want to know whether there is water up there?
Water is a very important molecule (as everyone on Earth knows from our own experience) and we want to know how much of it there is in the Solar System and where it is. For something that is so common on Earth, water seems to be in remarkably short supply on Venus, Mars and the Moon. We now believe that they all had lots of water initially, but either lost it to space (like Venus) or buried it below the surface, as on the Moon and Mars. Whether this is true, what happened to the water and what processes changed the climate on all of these Earthlike bodies is a topic of great scientific interest at the moment.
Another important reason for finding water is that it is an important resource – future astronauts will not be able to survive on the Moon for long without a water supply. Water is heavy and it would be expensive to bring the amount needed for a future manned Lunar base all the way from the Earth.
How does this fit into NASA’s broader programme of lunar exploration?
NASA plans to have a permanent presence on the Moon by 2020 or soon afterwards, and to go on from there to land a crew on Mars. There have been discussions to the effect that the European Space Agency, to which Britain belongs, may join in with the US programme of exploration, and the Chinese and Indian agencies have indicated that they each have plans for their own expeditions to the Moon.
Why is it important to explore space and its contents?
Three reasons:
1.To understand the origin and evolution of the Solar System and the planet upon which we live. What is the history of the Earth, and of the development of life? What parallels to this exist on other worlds?
2. To gain knowledge about how planets work so we can better understand and control our destiny on Earth. For instance, we now know that Venus has a hot climate for the basically same scientific reasons that the Earth is getting hotter. We need to understand the common Physics of the processes involved if we are to survive in the longer term.
3. Because it’s there! Humans love to explore, and most of us would like to know, for example, whether there is life on Mars.
Professor FW Taylor is the Halley Professor of Physics at Oxford University
