Jun 15 2018

More Evidence of Water on the Moon

As we contemplate not only more Moon missions, but establishing a long term base on the moon (Moonbase Alpha, of course) the question of how much water on the moon becomes pragmatic, and not just theoretical. It seems paradoxical – the Moon’s surface is the very image of a dry wasteland. How much water can there be?

Well, a new study supports prior evidence that there may be more water than you think trapped in the lunar soil, and in perpetually shaded craters at the poles. It is indirect evidence, but not unreasonable.

Japanese researchers have found moganite in lunar meteorites. They report:

Silica micrograins occur as nanocrystalline aggregates of mostly moganite and occasionally coesite and stishovite in the KREEP (high potassium, rare-earth element, and phosphorus)–like gabbroic-basaltic breccia NWA 2727, although these grains are seemingly absent in other lunar meteorites.

Basically moganite in a mineral of silicon dioxide. What is special about this particular crystal formation is that it only forms in the presence of water and high pressure. So if there is moganite in a lunar meteorite, that implies the moganite formed under the surface of the Moon, which means there may be significant water there.

The article makes specific mention that other examined lunar meteorites did not have moganite, but this actually supports the conclusion that the moganite was formed in the Moon. This is because an alternative hypothesis is that the moganite formed on the meteorite after it landed on Earth. But if this were true, then you would expect to find moganite on many or all of the meteorites found in the same location (meaning in the same Earth condition). The absence of moganite on the other meteorites means that the mineral probably did not form on Earth, which means it likely formed on the Moon.

Further evidence against terrestrial formation is the fact that the moganite is of higher concentration in the interior of the meteorite than on the surface. So it does not appear to have been formed from the outside by weathering. The other minerals mentioned, coesite and stishovite, are also forms of SiO2, and they can only form under high pressure, not during surface weathering on the Earth. Together these lines of evidence strongly suggest the moganite did not form on Earth.

Trying to think of other alternative explanations, I wonder how plausible it is that moganite can form by another process on the Moon that does not require water. Or, could the moganite have originated elsewhere in the solar system and then arrived on the Moon via a meteorite, and then subsequently been blasted into space and landing on Earth? I’m just riffing, and these explanations do not seem likely. So at least the moganite is reasonable indirect evidence of subsurface water on the Moon.

We have other more direct evidence of water on the Moon. The Chandrayaan-1, Deep Impact, and Cassini probes imaged the Moon’s surface with spectral analysis, showing the presence of hydroxyl (water) over the entire Moon. The concentration varied throughout the day, decreasing in direct sunlight, and was generally greater toward the poles.

Another line of evidence is water trapped in glass beads formed by volcanic activity on the Moon and brought back by the Apollo missions. Again this means water deep in the Moon, which is where the water would have been trapped in the volcanic glass.

There is also LCROSS – which was slammed into the Cabeus crater near the South Pole of the Moon, with water crystals and vapor imaged in the resulting plume.

OK, so we are pretty confident there is water on the Moon. There is great uncertainty as to how much. But there appears to be a lot of water at the poles, some water in the Lunar surface, and perhaps a lot of water at depth below the surface, and widely distributed throughout the Moon. Much of this water is in the form of OH (hydroxyl). It is still uncertain how we would extract it from the Moon and how much we would get.

One scientific question is where did the water come from? The three main hypotheses (which are not mutually exclusive) are that water came from the formation of the Moon itself, was deposited later from comets, and that water can form when protons from the solar wind smack into oxygen bearing minerals on the lunar surface. If you smack a proton (which is basically a hydrogen ion) into oxygen with sufficient energy, you can knock the oxygen out of its mineral and form a hydroxyl molecule.

All of this is of extreme interest to NASA and the world’s space organization, eyeing future missions to the Moon. Any sustained presence on Moon will need a source of energy, a source of oxygen, water, and food. Sending stuff to the Moon is expensive, so the more resources we can find on the Moon itself, the better.

The presence of water on the Moon can actually help with three of the necessary materials – water itself, of course, but also oxygen and fuel for energy production and rockets. In fact some futurists argue (plausibly, I think) that a lunar base would be the perfect launching pad for missions everywhere else in the solar system. There is much less gravity to contend with, and if you could fuel on the Moon that could be highly efficient.

This all depends on how feasible a Moon base is. Many also argue that we should focus on the Moon rather than Mars for a long term base or colony. The Moon is much closer, and so would be a lot easier to maintain. We can develop out technology for maintaining such bases on the Moon, and then apply that technology to Mars when the time is right.

Whatever path we choose to take, the presence of significant amounts of water on the Moon is a great thing for the future of space travel.

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