Water on the Moon

The Moon is generally considered to be dry. There are two reasons for that. The first is the generally accepted model for the formation of our moon is that something about the size of Mars collided with Earth and sent a huge amount of silica vapours into space at temperatures of about 10,000 degrees Centigrade (which is about twice as hot as the average surface of the sun) and much of that (some say about half) condensed and accreted into the Moon. Because the material was so hot and in a vacuum, all water should have been in the gas phase, and very little would condense so the Moon should be anhydrous deep in the interior. The fact its volcanic emissions have been considered to be dry is taken to support that conclusion. And thus with circular logic, it supports the concept that Earth formed by objects as large as Mars colliding and forming the planet.

The second is the rocks brought back by Apollo were considered to be anhydrous. That was because the accepted paradigm for the Moon formation required it to be dry. The actual rocks, on heating to 700 degrees Centigrade, were found to have about 160 ppm of water. On the basis that the accepted paradigm required them to be anhydrous it was assumed the rocks were contaminated with water from Earth. The fact that the deuterium levels of the hydrogen atoms in this water corresponded to solar hydrogen and not Earth’s water was ignored. That could not be contamination. Did that cause us to revise the paradigm? Heavens no. Uncomfortable facts that falsify the accepted theory have to be buried and ignored.

Recently, two scientific papers have concluded that the surface of the Moon contains water. Yay! If we go there, there is water to drink. Well, maybe. First, let’s look at how we know. The support is from infrared spectra, where a signal corresponding to the O-H bond stretching mode is seen. It has been known for some time that such signals have been detected on the Moon, but this does not mean there is water, since it could also arise from entities with, say, a Si-O-H group. Accordingly, it could come from space weathered rock, and in this context, signal strength increases towards the evening, which would happen if the rocks reacted with solar wind. The heating of rocks with these groups would give off water, so the Moon might still be technically dry but capable of providing water. Further examination of apatites brought back from Apollo suggested the interior could have water up to about 400 ppm.

How could the interior be wetter? That depends on how it formed. In my ebook, “Planetary Formation and Biogenesis” I surveyed the possibilities, and I favour the proposal outlined by Belbruno, E., Gott, J.R. 2005. Astron. J. 129: 1724–1745. Quite simply, Theia, the body that collided with Earth, formed at one of the Lagrange points. I favour L4. Such a body there would accrete by the same mechanism as Earth, which explains why it has the same isotopes, and while its orbit there is stable while it is small, as soon as it becomes big it gets dislodged. It would still collide with Earth, it would still get hot but need not vaporize. Being smaller, the interior may trap its water. There is evidence from element abundance that anything that would remain solid on the surface at about 1100 degrees Centigrade was not depleted, which means that is roughly the maximum temperature reached, and that would not vaporize silicates.

In one of the new papers, the signals from the surface have included the H-O-H bending frequency, which means water. Since it has not evaporated off into space it is probably embedded in rocks and may have originated from meteorites that crashed into the Moon, where they melted on impact and embedded the water they brought. There is also ice in certain polar craters that never see the sunlight, and above latitude 80 degrees, there are a number of such small craters.So, what does this mean for settlement? If the concentration is 5 ppm, to get 5 kg of water you would have to process a thousand tonne of rock, which would involve heating it to about seven hundred degrees Centigrade, holding it there, and not letting any water escape. The polar craters have ice up to a few per cent, but that ice also contains ammonia, hydrogen sulphide, and some other nasties, and since the craters never see sunlight the outside temperature is approximately two hundred degrees Centigrade below zero. You will see proposals that future space ships will use hydrogen and oxygen made from lunar water. That would require several thousand tonne of water, which would involve processing a very large amount of rock. It will always be easier to get water from the Sahara desert than the lunar surface, but it is there and could help maintain a settlement with careful water management.

Why do we do science?

What is the point of science? In practice, most scientists use their knowledge to try to make something, or solve some sort of problem, or at least help someone else do that. (Like most occupations, most junior ones turn up to work and work on what they are told to work on.) But, you might say, surely, deep down, they are seekers of the truth? Unfortunately, I rather fancy this is not the case. The problem was first noted by Thomas Kuhn, in his book, “The structure of scientific revolutions”. In Kuhn’s view, scientific results are almost always interpreted in terms of the current paradigm, i.e. while the data are reproduced properly, they are interpreted in terms of current thinking, even if that does not fit very well. No other theory gets a look-in. If a result does not conform to the standard theory, the researcher does not question the standard theory. The first effort is to find some way of accommodating it, and if that does not work, it may be listed as a question for further work, in other words the researcher tries to persuade someone else to find a way of fitting it to the standard paradigm rather than taking the effort to find an alternative theory.

According to Kuhn, most science is carried out as “normal science”, wherein researchers create puzzles that should be solved by the standard paradigm, in other words, experiments are set up not to try to find the truth, but rather to confirm what everyone believes to be true. This is not entirely unreasonable. If we stop and think for a moment, an awful lot of such research is carried out by PhD students, or post-doctoral fellows. The lead researcher has submitted his idea as a request for funding, and this is overseen by a panel. If you submit something that would not get anywhere within the current paradigm, you will not get funding because the panel will usually consider this to be a waste of time. On top of that, if you are going to include a PhD student in this work, that student needs a thesis at the end of his work, and that student will not thank the supervisor for coming up with something that does not produce results that can be written up. In other words, the projects are chosen such that the lead researcher has a very good idea as to what will be found, and it will be chosen so that it is unlikely to lead to too great an intellectual challenge. An example of a good project might to make a new chemical compound that might be a useful drug. The project might involve new synthetic work, there will be problems in choosing a route, but the project will not founder on some conceptual problem.

Natually, the standard paradigm clearly must have much going for it to get adopted in the first place. It cannot be just anything, and there will be a lot of truth in it, nevertheless as I mentioned in my first ebook, part 1 of “Elements of Theory”, any moderate subset of data frequently has at least two theories that would explain the data, and when the paradigm is chosen, the subset is moderate. If all that follows it to investigate very similar problems, then a mistake can last. The classic mistake was Claudius Ptolemy’s cosmological theory, which was the “truth” for over 1600 years, even though it was wrong and, as we now recognize, with no physical basis. If you wish to find the truth, you might follow Popper and try to design experiments that would falsify such a theory, but PhD theses cannot be based like that as it is too risky that the student will find nothing and fail to get his degree through no fault of his.

What brought these thoughts on was a recent article in the journal Icarus. The subject was questioning how the Moon was formed. The standard theory of planetary formation goes like this. After the star forms, the accretion disk that remains settles the dust on the central plane, and this gradually congeals into larger bodies, which further join together when they collide, and so on, until you get planetesimals (objects about the size of asteroids) then, apart from the asteroids, eventually embryos (objects about the size of Mars) which gravitationally interact and form very eccentric orbits, and then collide to form planets (except for Mars, which is a remaining embryo). All such collisions once planetesimals form are random, and the underpinning material could have come from a very large region, thus Earth was made from embryos formed from material beyond Mars and Venus. The Moon was formed from the splatter arising from a near glancing collision of a Mars-sized body called Theia with Earth.

If you carefully measure the isotope ratios of samples of meteorites, what you find is that all from the same origin have the same isotope ratios, but those from different parts of the solar system have different ratios. As an example, oxygen has three stable isotopes of atomic weights 16, 17 and 18. We have carbonaceous chondrites from the outer asteroid belt, a number of samples from Vesta, some from Mars, and of course unlimited supplies from here. The isotope ratios of these samples are all the same from one source, but different between sources. We also have a good number of samples from the Moon, thanks to the Apollo program. Now, the unusual fact is, the Moon is made of material that is essentially identical to our rocks, at least in terms of isotope ratios.

This Icarus paper carried out simulations of planetary formation employing the standard theory, and showed that since the Moon is largely Theia, the chances of the Moon and Earth having the same ratio of even oxygen isotopes is less than 5%. So, what conclusion do the authors draw? The obvious one is that the Moon did not form that way; a more subtle one is that planets did not form by the random collision of growing rocky bodies. However, they drew neither. Instead, they really refused to draw a conclusion.

I should add that I have in interest in this debate, as my mechanism outlined in Planetary Formation and Biogenesis has the planets grow from relatively narrow zones, although the disk material is always heading towards the star to provide new feed. The Moon grows at the same distance as Earth (at a Lagrange point) from the star and hence has the same composition. The concept that the Moon formed at either L4 or L5 was originally proposed by Belbruno and Gott in 2005 (Astron. J. 129: 1724–1745) and I regard it as almost dishonest not to have mentioned their work, which predicts their result provided the bodies form from local material. Unfortunately, the citing of scientific work that contradicts the standard theory is not exactly frequent, and in my view, does science no service. The real problem is, how common is this rejection of that which is currently uncomfortable?

You may say, who cares? It may very well be that how the Moon formed is totally irrelevant to modern society. My point is, society is becoming extremely dependent on science, and if science starts to become disinterested in seeking the truth, then eventually the mistakes may become very significant. Of course mistakes will be made. That happens in any human endeavor. But, do we want to restrict them to unavoidable accidents, or are we prepared to put up with avoidable errors?