A Dry Moon
On 13 November 2009, the LCROSS
mission put out a press release
announcing that they had found water on the moon. This caused quite a stir and was picked up by many newspapers, as we had always understood the moon to be a fantastically dry and arid place. What did this new discovery mean? How embarrassing for all those science teachers who’d taught that there was no water to be found on the moon!
However, the idea of a wet moon is not as new as one might think. Study a map of the moon and you’ll find any number of seas, bays, oceans and other watery features. The first people to watch the moon through telescopes had noticed that there were many darker regions which seemed smooth and featureless, compared to the lighter areas which were full of craters and mountains, and reasoned that they might be oceans and lakes. The convention was to name
these after moods, weather, and natural phenomena (Seas of Tranquility, Rain, Cols and Fertility, for example). These names are usually written in the latin form (Maria Tranquilitatis, Maria Imbrum, etc)
As telescopes improved, though, small craters and hills became visible even in the seas and it became obvious that they could not filled with water after all. Gradually it became clear that the moon was an arid dry place, lacking even an atmosphere, and this was finally confirmed in the public eye when the crew of Apollo 11 set foot on the moon.
However, in March 1998, mission scientists for the Lunar Prospector probe announced that they had detected high levels of hydrogen deep within craters on the Moon’s North and South poles. It was theorised that this could indicate the presence of water, since the insides of those craters would be permanently shadowed, which would protect any water ice from the unshielded heat and radiation of the Sun. In an effort to prove their theory, the Lunar Prospector was crashed into one of these craters on 31 July 1999 (after it had used up most of it’s fuel and was nearing the end of it’s life). The hope was that the impact would throw up a plume of debris which could then be analysed from earth-based telescopes for water vapour. Unfortunately, the experiment was not successful, so another mission was planned specifically to smash into the lunar surface and try again.
This mission was called LCROSS (Lunar CRater Observation and Sensing Satellite), and was composed of three separate spacecraft. The first, the LRO (Lunar Reconnaissance Orbiter, strictly speaking a separate mission) separated from the main mission early on, and went into orbit around the moon. The LRO is built like a spy satellite, and is designed to map the moon by taking high resolution photographs of the entire lunar surface (It is so successful that we now have satellite photographs of the equipment and footprints left behind by the various Apollo missions!). The other two craft were an Impactor and a ‘Shepherd’. The Shepherd’s mission was to observe the Impactor’s crash, photograph and record all details, and beam them back to earth before it too crashed into the same crater.
Mission scientists anticipated a big enough crash that amateur astronomers might be visible from earth with amateur equipment, and many amateur astronomers stayed up late with their telescopes fixed on the target crater. In the end, the plume was not visible, and initial community reports expressed disappointment. Back at mission control, however, the results were far more exciting. Infra-red imagery showed a huge cloud of dust and debris spraying up from the impact sites which wasn’t seen in visible light because it was still in the shadow of the crater. But far more important than these pictures were the spectrographic analyses of the light coming from the impact. Showing appropriate care and diligence, the mission scientists spent more than a month carefully analysing the data and double-checking their results before going public with the result: There is definitely water on the moon!
The practical ramifications are huge. Space travel is a massively expensive business, because of the simple physics of getting a payload all the way out of Earth’s gravity well (A rather woolly way of saying “Achieve escape velocity”, which means only that it is going fast enough to not simply fall back down to the ground) — it requires so much energy that you have to pack many tonnes of fuel, which in turn increases the weight, so you need an even bigger engine, with more fuel, which adds weight, until you eventually end up with the gigantic spacecraft we have today, which are almost entirely fuel tank! No wonder, then, that they are built in stages, each of which is discarded once it is out of fuel – it’s to save weight for later in the mission!
This makes it extremely difficult to get basic supplies like food, water and oxygen out to any bases we build. A base on the moon is massively further away than the ISS, and logistics would be impossible. But, now that we know there is water, a lunar base can simply mine their own water. The water can be used to irrigate gardens or farms to grow food, and it can be cracked electrically to make hydrogen and oxygen – rocket fuel. With an ample source of fuel way up out of Earth’s gravity well, travel to the rest of the solar system becomes much simpler (although not yet easy!).
So this one mission, crash-landing into the moon, has proved beyond doubt that humanity has a future beyond planet earth. We CAN get out there, we CAN stay there, we CAN rekindle our dormant pioneering spirit and spread our wings into the cosmos. And that’s just the most fantastic news I’ve heard in years!
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