Moon actually dryer than dem dry bones, say boffins
Kybosh put on lunar ice-mine rocketfuel bonanza plans
Spoilsport boffins, carrying out a new analysis of lunar rocks brought back by the Apollo missions of yesteryear, have pooh-poohed the notion that there are copious amounts of water to be found on the Moon. The research might be thought to have finally dashed hopes of mining lunar ice for cheap rocket fuel, but in fact President Obama had largely killed off such plans already.
The boffins' failure to squeeze water from moon stone was reported last week in hefty boffinry mag Science. It seems that the key to the business is the comparison of different isotopes of chlorine. Where chlorine has been reacting with hydrogen a lot in the past - as where plenty of water is about - it is well mixed, meaning that the amounts of different chlorine isotopes are almost exactly the same in any sample. This is the case where chlorine is examined in samples from moist Earth; isotope ratio is always the same.
Lunar chlorine, however, has hugely different ratios of isotopes from sample to sample - the ratios "scatter". This indicates that the chlorine hasn't been having an exciting time in the past reacting with hydrogen, as on wet Earth, but rather has simply sat about locked up in the dry lunar desert.
"The only process we are aware of that could cause such large isotope scatter is if the hydrogen content of the moon is 10,000 to 100,000 times less than [that of] Earth," according to geochemist Zachary Sharp, quoted by Science.
The results clash somewhat with readings from instruments aboard space probes in orbit around the Moon, which seem to show the presence of noticeable amounts of hydrogen - theorised to be present as part of water molecules - in some lunar locations. NASA's LCROSS impact probe, which crashed into the Moon's south pole last October, has also apparently detected "buckets" of water ice lying frozen in the sunless craters of the lunar antarctic.
The question of whether there is water on the Moon, and if so how much, is more important than it might seem at first. If water is there, it could be split into hydrogen and oxygen using solar or nuclear power, so furnishing a supply of rocket fuel which would not have to be shipped from Earth. This would make the movement of cargo and passengers to and from the Moon hugely cheaper: under normal assumptions, much of what a lunar mission carries out is fuel for the return journey. Furthermore, water and oxygen sourced from it would make a manned Moonbase cheaper to run.
That may all be a bit irrelevant these days. The planned Constellation manned moon missions, for which LCROSS and the orbiting LRO moonsat were to be merely the forerunners, failed to attract sufficient funds from Congress to make them viable. President Obama now plans to proceed directly to near-Earth asteroids and so to Mars, possibly hoping to sidestep the budget issue by using new and potentially much cheaper launch rockets rather than recycled Apollo and Shuttle technology as called for by Constellation.
Even without manned NASA Moon missions, however, lunar water could still be important. The cost of hoisting mass up out of Earth's gravity is so great that lunar-water rocket fuel - which would only have to be carried up out of the moon's much shallower gravity well - could perhaps be cheaper to supply in Earth orbit than Earthly sources could manage. Abundant lunar ice mines could find lucrative business refuelling valuable satellites orbiting Earth; at present a satellite must normally be destroyed and replaced by a new one when its onboard supplies of manoeuvring fuel run low.
If large missions ever do set out regularly from Earth orbit to the planets, they too might be glad to get their fuels relatively cheaply from the Moon rather than having to blast every gram of mass up through Earth's six-times-greater gravity. That said, in the case of manned missions, the need for greater speed than ordinary chemical rockets can offer may mean that different kinds of fuel than hydrogen and oxygen are required.
But Sharp and his colleagues' research seems to indicate that ice on the Moon may be rare stuff indeed, perhaps deposited as a thin rime by comet impacts and preserved only in the freezing, sunless crater bottoms of the lunar poles. Getting any substantial amount of it together if this is the case would call for a prohibitive amount of effort. ®
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