Stardate 20020521.1454

(On Screen): The Chinese are trying to create the world's third independent space travel technology. I wish them well. It's a tough problem, but the more of it there is, the happier I'll be.

They want to go to the Moon, and it's about time someone did. It will take a long time, but it's our destiny in the long run.

China's space program is more than three decades old. It launched its first satellite in 1970 and fires payloads into orbit for American, European and other clients aboard giant Long March rockets.

The government announced plans in 1992 for manned flight and a space station. Officials say they want to mine the moon and explore Mars.

I don't know about that "mine the moon" part, though.

One of the great questions in geology has been just how it is that ores and other valuable concentrations of minerals form. Some of them occur as the result of the actions of life (such as the creation of coal, limestone or chalk). Right now there's no reason to assume that the Moon has ever had any substantial amount of life.

Most of the non-organic ways of creating ores seem to involve liquid water and a lot of time. Generally speaking, there will be some large formation which contains a slightly higher concentration of something soluble, and water will seep through it, leech out the minerals, and then move to somewhere where the water is separated from the dissolved minerals, which are deposited at that location.

The actual mechanisms involved can be quite varied and may be extremely involved. Rock salt is created by a two-step process. First, rain water has leached sodium and chlorine out of the land and carried it to the sea. The process of evaporation separates water from the salt, leaving it behind, and the water is carried over the land to again fall as rain and continue the process. Repeat for 2 billion years, and you end up with a considerable amount of salt in the ocean. Then put a lot of that salty water into a place where it evaporates, and it leaves rock salt behind. Sometimes that happens in huge quantities relatively rapidly, such as during the interval when Gibraltar closed and the Mediterranean dried up leaving a layer of rock salt which is still present under the sea.

It can also happen slowly. In Africa's Great Rift Valley, there are places which are dry and below sea level. At one such place there are what seem to be springs, but the water is salty, not fresh. It turns out to be water leaking in from the Indian Ocean. But the water evaporates as fast as it flows in, and the salt is slowly accumulating. In a few thousand years there's going to be a very large deposit of salt there (unless something geologically interesting happens to either cut the flow or drastically increase it).

One of the major ways that ores form was only discovered in the last thirty years, by the ALVIN submersible. This happens deep in the ocean, where pressures are extremely high. Water at very high temperature (well above 100° C, which is prevented from boiling by the pressure) seeps through the rocks and dissolves minerals. It then spouts into the ocean in undersea hot springs. As the water is cooled, the minerals it carries precipitate out on the ocean floor. Conditions necessary to do this are now and always have been quite common, and it's thought that this process is primarily responsible for most of the major metallic ores that we now mine commercially.

The problem is that none of this could have happened on the Moon, because there have never been substantial amounts of liquid water there.

The only process I know of where minerals can be concentrated without water or life involves large magma bodies. When they sit for very long periods without cooling, a certain amount of separation based on density will take place. It seems to me that this is the only one which could probably operate on the Moon. But this process is much less efficient, and where the hot-spring deposition method may well produce nearly pure ore bodies, about the best that can be hoped for from this is a slight increase in concentration.

Large amounts of moon rocks were brought back during the Apollo moon exploration program. Meteoric rocks from the moon have been found on earth, as well, and have been studied. The mineral formation of the Moon is pretty well understood, and it is not very remarkable. Certain cool lava flows are somewhat high in titanium (between 1% and 14%) but aside from that the main thing you find is aluminum, silicon and oxygen in the form of rocks similar to those found on Earth. We do not use those rocks commercially because we have better ores available which are far more pure. None of what we know of on the Moon would be worth mining and bringing back here; the cost of transport would far exceed the value of the minerals involved.

The Moon may well be worth mining eventually, not so much because of what is there as because of where it is: out of Earth's gravity well. It makes no sense to bring it here, but it is well placed for use in making spacecraft eventually to explore the rest of the Solar System. It should be relatively easy to refine aluminum there by heating aluminum-bearing rocks with large mirrors, using free solar energy. Oxygen can be released from silicates the same way. So you would boost the high-tech components of a space craft (i.e. electronics, engines) from Earth, but make the heavy structural pieces on the Moon. Both aluminum and oxygen would be immensely valuable when the time comes to build a moon colony (and glass produced from the silicates may also be useful).

But for the moment, about all we know of on the Moon which might be worth bringing back are the rocks themselves, for purposes of research or to sell as souvenirs. Doing so on an industrial basis seems unlikely to be worthwhile.