August 7, 2010
Nobody knows ….. how dry I am
Apollo 16 sample 60095, "Rusty Rock" -- contamination or Moon water?
The never-ending saga of water on the Moon continues apace. In the latest revelation, it is now claimed that the Moon is indeed “dry” after all and never had much water (this new finding is only in regard to endogenous lunar water contained inside the Moon, not to water that has been or is being added to the lunar surface from impacting debris). Details of the controversy illuminate not only how science is done, but also how science is reported to the public by the popular press.
The current study by scientists at the University of New Mexico did not measure lunar water directly, but rather a chemical proxy for it, the element chlorine. Chlorine is “hydrophylic” (water-loving) and in theory, its abundance and variations should track with those of water inside the Moon. The new study finds that while the ratio of isotopes of chlorine largely are invariant in Earth rocks, they vary widely on the Moon. The interpretation of this observation is that the Moon does not possess an “offsetting” mechanism that regulates terrestrial chlorine isotope ratios, and the biggest offsetting factor in such systems is the hydrogen present in water in the Earth’s interior. The conclusion of this study is that as this factor is absent from the studied lunar samples, the Moon has no large amount of water nor did it ever have any.
Back in 1972, a “rusty rock” – sample number 66095 – was brought back to Earth by the Apollo 16 astronauts. Lunar scientists have long debated the origin and meaning of the molecule hydroxyl (OH) in the mineral akaganite (an oxidized iron compound) that was identified on its surface. Does this famous “oddball” rock sample indicate the movement of and interaction with water and the lunar surface, or did the akaganite form inside the warm, humid Apollo 16 command module during its transport to Earth?
Results from the University of New Mexico study are not inconsistent with what we’ve known about the Moon for some time. Almost all of the Apollo samples are bone-dry (showing no hydrous mineral phases) and chemically reduced, indicating formation in a non-oxidizing environment. Such conditions are possible in the absence of water. Conventional wisdom that the Moon has no significant water derives from these and similar observations.
A 2008 analyses of lunar samples promised to change our perception of water and the Moon. Studies of beads of volcanic glass from the deep interior and grains of the mineral apatite in several types of lunar rock surprised us by the presence of water (H2O) or its related ion hydroxyl trapped in both the glass and mineral grains. The amounts of water detected were still quite small (a few tens of parts per million), but significantly greater than previously reported. Much was made of these new discoveries, including the suggestion that models of lunar origin would have to be reconsidered and perhaps revised.
Do the newly released study results negate previous work? Hardly. What’s true for one part of the Moon may or may not be true for another. Scientists must separate their observations from the subsequent inferences drawn from those observations. Unless some error is made, the previous measurements of water in a sample are objective facts. What the presence of that water means is something else. The interpretation of facts draws on our understanding of how nature works and the completeness of our reconstruction of the history of the Moon; both are incomplete at best and just plain wrong at worst. Moreover, there is a tendency for scientists to want their results to be significant. Thus, they will sometimes draw broad, sweeping planet-wide conclusions that may not be justified by the actual observation. I know this happens because I have done it myself. There is no intent to falsify or mislead – only a desire to claim a fullness of understanding that may not yet be warranted.
When esoteric or complex arguments are made about the meaning of some discovery, it is sometimes very difficult for the popular press to fully follow the lines of reasoning. They also have a desire to make stories interesting to their readers, so they tend to focus on controversy, often portraying different interpretation of facts as “fights’ between rival scientific groups. These tendencies often result in hilarious headlines, e.g., “Moon not so watery after all” or my personal favorite, “Moon water dreams evaporate.” Funny – I don’t recall ever “dreaming” about water in the Moon and I very much doubt that many of my colleagues do either. But differing opinions means conflict and conflict means human interest, and so a fight it must be.
Nature is complicated and that can make for some missteps in our long struggle to characterize it and reconstruct its history. The simple fact is, the Moon is more complex and interesting than we had thought. Scientifically, this is a good thing. We want hard problems to tackle and solve. And the process of solving problems sometimes does create feuds between scientists; history is replete with them. However, in this latest instance, a feud doesn’t exist – only a desire to fully understand the Moon and its history. When Prohibition is repealed and we return to the Moon, many of our questions can be answered and there will be no need to dream up non-existent controversies with hyperbolic and misleading headlines.
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Seeing as we have physically explored less than 1,000 meters of the Moon (I’m being generous with that measurement), it’s foolish to proclaim that Luna is bone dry inside.
Until we are able to dig down to a greater depth, we can’t be sure how wet the Moon is underneath. We still need more samples.
Until then, this is at best a theory (albeit one supported by partial evidence)
Comment by Darnell Clayton — August 7, 2010 @ 11:53 am
One major scientific advantage for a Moon base is that it could serve as a central deployment area for robots teleoperated from Earth. Such robots could rove about the entire lunar surface providing videos of different regions while collecting samples. The robot rovers could bring those samples back to the Moon base for examination and even export back to Earth.
Some of these roving robots could even be equipped with short range rockets enabling them to jump in and out of large craters for sample collection.
Lunar base deployed robots could actually allow NASA scientist back on Earth to do substantially more video exploring and sample collection on the lunar surface than astronauts living at a lunar facility. NASA astronauts would simply bring those robot collected samples back with them when they return to Earth.
Comment by Marcel F. Williams — August 7, 2010 @ 2:28 pm
Thanks, once again, Dr. Spudis.
I was just sorting through the feeds, getting more disturbed by the more prestigious, supposedly more “credible” news sources, happily reporting this latest study as conclusive, apparently delighted, to throw cold water on cold traps and the newly sensed lunar hydrological cycle.
Thanks for jumping on this.
Comment by Joel Raupe — August 7, 2010 @ 6:46 pm
Dr. Spudis is right. This is how science works. There are some tracers that suggest water, and others that do not. Reconciliation of those is the nature of the game. But what this shows quite clearly, it seems, s how unready we are to develop the Moon as a water-bearing site for humans. We’d be far better off developing our technologies to make human space flight more economical, and putting a raft of robotic craft on the Moon to help to fully understand to what extent water might actually be available to people there.
You sure don’t need a Moon base with humans as an outpost for such robotic craft. That makes no sense at all, given how hugely expensive it would be to put people there compared to what it would take to put robots there. If you want to send samples back to the Earth, why in the world do they have to come back in the pockets of astronauts?
I would call the new plan less of a “prohibition” of humans on the Moon, but a smart perspective on where humans could do the most good.
Comment by Heinrich Monroe — August 7, 2010 @ 7:49 pm
Heinrich,
But what this shows quite clearly, it seems, s how unready we are to develop the Moon as a water-bearing site for humans
Actually, it shows nothing of the sort. The issue of endogenous lunar water has nothing to do with the presence and quantity of polar exogenous water as a resource.
I agree that we should plan for a series of robotic missions to characterize the nature of the polar water — where it is, how much there is, its physical state. That can and should be part of a general plan to develop a lunar outpost. Much of the resource development of the Moon can be done with robotic machines, but we still need people there to fix and maintain those systems.
And in contrast to your assertion, the “conventional wisdom” that it cannot be done under existing budgets is simply wrong. The anti-Vision calls for even more money to be spent than had been planned — the difference is that with the new plan, we won’t get anything for it.
Comment by Paul D. Spudis — August 8, 2010 @ 4:42 am
A couple of questions. What is the best evidence to date of lunar surface water on either poles. How likely is it that lunar polar water is in sufficient concentrations so that it could be extracted economically?
Second, working with lunar polar ice involves spending more energy to getting to and from the lunar poles AND having to work in environments with incredibly low temps. Since oxygen is 89% of rocket fuel, and with large quantities of oxygen at the lunar equator, should we still be looking at extracting water from the lunar poles?
Comment by JohnHunt — August 8, 2010 @ 12:42 pm
JohnHunt,
What is the best evidence to date of lunar surface water on either poles. How likely is it that lunar polar water is in sufficient concentrations so that it could be extracted economically?
Multiple lines of evidence suggest the presence of water. The most definitive piece of evidence to date is the water seen during the LCROSS impact at the south pole last October. That measurement indicated between 5 and 10 weight percent water is present in polar soils. That’s at least two orders of magnitude greater than our previous highest estimate. If our Mini-RF radar interpretation is correct, there are places near both poles consisting of nearly pure water ice, but that interpretation needs confirmation by analysis on the ground.
Second, working with lunar polar ice involves spending more energy to getting to and from the lunar poles
Not true. If you stage your lunar landing from and back to Earth-Moon L1, it costs no more to go to a pole than it does to land anywhere else. Energetics are dependent upon architecture.
AND having to work in environments with incredibly low temps.
It’s easier and less power intensive to keep warm in space than it is to keep cool. Moreover, the poles provide places with near-permanent solar illumination, which not only allows us to generate electricity through solar arrays, but provides a benign, near-constant thermal environment as well. Machines will be doing most of the work in the cold traps, not people.
Since oxygen is 89% of rocket fuel, and with large quantities of oxygen at the lunar equator, should we still be looking at extracting water from the lunar poles?
Yes, for two reasons. First, oxygen by itself doesn’t buy you much — the key to propellant manufacture is oxidizer and fuel. The mass of hydrogen is low, but its “overhead” mass of tankage, refrigeration units to minimize boil-off, and supporting infrastructure make it essential to use lunar hydrogen if available. Mining lunar water gives us both with relatively little energy expenditure.
Second, the oxygen in lunar materials is very tightly chemically bound to metals. It takes significant energy to break these bonds and recover the oxygen. So on a per mass unit basis, it is significantly easier and cheaper to harvest water for H2 and O2 than it is to make it out of “dry” equatorial lunar soil. By the way, that same argument applies to asteroid resource usage as well.
Comment by Paul D. Spudis — August 8, 2010 @ 1:17 pm
The media stupidity continues! Just when I thought I had a winner in my “World’s stupidest lunar water headline” contest, a new contestant blows away the competition:
Moon actually dryer than dem dry bones, say boffins
Kybosh put on lunar ice-mine rocketfuel bonanza plans
It’s not even worth my time to rebut the idiocy.
Comment by Paul D. Spudis — August 9, 2010 @ 7:00 pm
[...] of volatiles at the poles of the Moon (discussed in my blogging many times, most recently HERE) and the infamous phenomena of Lunar Transient Phenomena (LTP), described as glowing reddish [...]
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