Wednesday, December 2, 1998 Published at 01:59 GMT
Moon map aids discovery
The red indicates an abundance of helium-3 on the Moon's surface
By BBC News Online Science Editor Dr David Whitehouse
Future prospectors on the Moon may be assisted by an intriguing new lunar map developed by scientists in Arizona and Hawaii.
It shows places where the element helium-3 can be found in the lunar dirt. Helium-3 is rare on Earth, but more common on the Moon.
Its importance lies in the fact that it could be an efficient fuel for nuclear fusion reactors.
Fusion reactors are still under development and it will be many decades, if ever, before they provide power commercially.
But they have many advantages over conventional nuclear reactors in that they produce far more power and produce much less radioactive waste.
Today's design of fusion reactor uses tritium as a fuel, an isotope of hydrogen extracted from sea water. But Helium-3 would be even more efficient and produce even less radioactive waste.
The helium-3 found in the lunar soil comes originally from the Sun. A stream of particles from the Sun, called the solar wind, contains helium-3 which is deposited on the Moon's surface.
The factors taken into account by the researchers in mapping the likely abundance of helium-3 in a given area of the Moon are the exposure age of the Moon's surface matter, or regolith; the amount of helium-3, arriving from the Sun in the solar wind and the titanium content of the lunar soil.
Older regions of the Moon's surface should be better sources of helium-3 because they have been exposed to the solar wind longer and contain greater amounts of fine-grained aggregates that absorb helium-3.
Taking this into consideration, the scientists estimate that the greatest amounts of helium-3 will be found on the far side in the maria, or "seas," of the Moon.
Helium-3 could also be found in near side areas where high concentrations of titanium dioxide help trap the isotope.
Even though helium-3 is more abundant on the Moon than on the Earth, it is still very rare amounting to only 4 or 5 parts per billion in the lunar soil.
To extract one tonne of helium-3, it is estimated that 200 million tonnes of lunar soil would have to be processed. That is equivalent to mining the top 2 metres of a region 10 kms square.
Some scientists believe that in the future it could be worth it. It would only require 25 tonnes of helium-3 to provide all the power that the United States needs in a year.
Energy calculations suggest that the energy gained from Helium-3 mined on the Moon and shipped back to Earth would be 250 times that used to obtain it.
When the first lunar colony is established, perhaps in 20 years time, it is likely to be positioned near the Moon's south pole, near the so-called 'Peak of Eternal Light.' This mountain is in perpetual sunlight so solar panels on its slopes would provide constant energy.
Later colonies may move down onto the older lunar plains and set up strip-mining factories to extract helium-3 as well as hydrogen which can be used as a rocket fuel.