September 25, 2009
Water, water everywhere….
Water-bearing minerals on the Moon (in blue). (Chandrayaan M3 Team and NASA)
The extreme dryness of the Moon is established scientific dogma. The study of Apollo rock and soil samples pretty much had convinced scientists that the Moon has no water. Because its surface is in a vacuum and experiences extreme temperature swings at the equator (from -150° to 100° C), the Moon was believed to have a bone dry surface. Moreover, minerals that make up the lunar rocks not only have no water, but crystallized in a very reducing, waterless environment, indicating no significant water at depth.
Yet, some irritating facts suggested that the whole story was more complicated. Water is being added to the lunar surface. We know the Moon is bombarded with comets (mostly water ice) and meteorites rich in water-bearing minerals. Additionally, the solar wind (mostly hydrogen atoms or protons) constantly hits the surface, implanting itself into the dust grains and a possible source for the creation of water. An experiment laid out on the surface by the Apollo astronauts observed water vapor after the crew left the Moon. It was thought this vapor might be latent out-gassing from the Lunar Module descent stage, but scientists couldn’t be sure.
So what happens to all this water? Most of it is thought lost to space by a variety of processes, including dissociation by sunlight, thermal loss from the extremely high daytime temperatures, and sputtering induced by the impact of high-energy particles from space. Some areas near the poles of the Moon are permanently dark and cold, so if any of this stray water happened into them, they would be “trapped” forever in the dark areas. And although an extremely slow process, over millions of years a considerable amount of water ice might accumulate. But we don’t know how much water is made and how much might be present on the Moon.
Just published results from spectral mapping instruments on three different spacecraft indicate the presence of large amounts of either water or the OH molecule in the soils of the Moon. This water is present at high latitudes at both poles and occurs in sunlit areas (these instruments rely on reflected sunlight). Although the authors of these new results don’t understand the source of this water, they favor the creation of water by the interaction of solar wind with surface minerals. Solar wind protons reduce metal oxides in the soil, creating free metal (usually pure iron, Fe0) and water. The M3 Team suggested that this water might act as a source for the water believed to be trapped in the dark polar cold traps.
What’s surprising about this new data is not the presence of water, but its pervasiveness. The published image (above) shows this water to be present from the poles down to about 60° latitude. This area subtends over 10 million square kilometers, or about one-third the surface area of the entire Moon! Although the water appears to be present only in the upper few millimeters of the surface, its total mass could be enormous, greatly exceeding the several hundred million tones estimated to be present as ice in the dark areas of the poles.
As always with good science, the new results raise many more questions than they answer. In part, this is a “chicken or egg” issue – do the newly discovered deposits result from surface alteration by water derived from the polar ice, or do they serve as a source for such deposits? How does water form, move, get destroyed or get cold-trapped on the Moon? What are rates of water deposition and removal? What and where are the ice deposits and how pure might they be? Right now we can only dimly perceive the beginnings of a whole new sub-discipline of lunar studies: polar geoscience.
This exciting story isn’t over. More developments in this field are on the horizon. Results from other experiments carried aboard the Chandrayaan-1 spacecraft, including my own Mini-SAR imaging radar, have yet to be fully reported. The American Lunar Reconnaissance Orbiter (LRO) mission is settled into its mapping orbit and will be examining the Moon in detail over the next couple of years. Every time we get new data from the Moon or examine and map it with some new technique, we learn new and surprising facts.
In a future post, I’ll examine the implications of large amounts of lunar water for human return to the Moon and the possibilities for a permanent sustainable presence on our nearest planetary neighbor.
Stay tuned – things are getting very interesting.
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Quoting Arthur C. Clarke from 1951, “The first lunar explorers will probably be mainly interested in the mineral resources of their new world, and upon these its future will very largely depend.” The Augustine Committee clearly showed that we cannot get humans to the Moon anytime soon with NASA’s current budget and thinking. A huge increase in NASA’s budget (though small when compared to stimulus bills and bailouts of the banking system and auto industry) is not likely. So, what do we do? While we spend the next decade extending the human use of the International Space Station, and coming up with a new US human space transportation system, we can also be sending robots to the Moon, to continue exploration of the lunar surface and begin lunar resource utilization and development in preparation for a human presence sometime in the late 2020s or early 2030s. Robotic exploration and development of the Moon during 2010-2020 is an affordable, incremental step along the path of human expansion into the solar system, that subsequent steps could benefit from. Does this last sentence sound familiar? It should, it was espoused by Clarke and von Braun in the 1950s, more recently by the Augustine Committee, and by plenty of other people in between. Going back to the Moon does not have to start out like another big NASA rocket program. It just requires some old thinking, and some new implementing.
Comment by John G. — September 25, 2009 @ 11:59 am
Although the water appears to be present only in the upper few millimeters of the surface,
This is because the IR measurements can only sense that thin layer, right, not because there is evidence of absence at great depth?
Comment by Paul F. Dietz — September 25, 2009 @ 2:38 pm
Paul,
Yes, although in the Science paper, Carle Pieters makes the point that in some areas, she can see the water feature but the Lunar Prospector neutron spectrometer reports nothing. The NS samples depths down to about 30 cm. But this is only in one lower latitude area. Polar data, both NS and radar, sample to depths of a few tens of cm to a few meters.
Comment by Paul D. Spudis — September 25, 2009 @ 4:22 pm
Very exciting developments. LCROSS can only yield new clues and greater understanding, I’m so anxious for that on October 9th. As for where the hydroxyl exists in which layers, or from whence it can be coaxed with new extraction technologies, it’s also exciting to think that we don’t know the whole story yet. Think how many lunar samples we’ve had since 1969, but only now have developed techniques to unfold this amazing story. i’m thinking this is the tip of the proverbial lunar iceberg…
Comment by Pillownaut — September 25, 2009 @ 8:23 pm
@ John G.
The Augustine Committee clearly showed that we cannot get humans to the Moon anytime soon with NASA’s current budget and thinking.
Nevertheless, that does not entail that it cannot be done. Cf. the recent proposal by ULA that just came out. They can get boots on the ground permanently by 2018.
A Commercially Based Lunar Architecture
@ Dr. Spudis:
What about the fumaroles? Do you think they play a role in the lunar hydrology?
Comment by Warren Platts — September 27, 2009 @ 9:39 am
What about the fumaroles? Do you think they play a role in the lunar hydrology?
Although we cannot totally rule out anything at the moment, I doubt it. Fumeroles are associated with volcanic activity and the vast bulk of the Moon has been volcanically dead for billions of years. This water must be geologically young, otherwise it would have been lost to space and destroyed. In fact, its pervasiveness argues for its current, continual formation on the Moon. A more likely origin is solar wind reduction of silicates in the existing rocks. This newly formed water may eventually migrate to the polar cold traps.
Comment by Paul D. Spudis — September 27, 2009 @ 10:47 am
Dr Spudis,
I was trying to describe how much potential water was on the Moon to a friend of mine in terms he would understand. According to your article and others, I have read;
Assuming that H20 (I understand that research is talking about OH) is present at a concentration of 1 part per 1,000 by volume over 1/3 of the Moon’s surface and we extracted the water with 100% efficiency by strip mining one meter deep, we would expect to collect approximately 12.6 km^3 of water. Approximately 1/3 the volume of Lake Meade (volume of Lake Meade is approximately 35.2 km^3).
Have I calculated that correctly or have I understated the potential volume somehow?
Thanks,
Russell
Comment by Russell — September 28, 2009 @ 2:44 pm
If the theory that THERA collided with the Earth, creating both a larger Planet and of course the Moon, are correct then I think this data provides more ammunition for the seeding of Earth from Space. Not only in terms of Organics from the Kuiper Belt and Oort cloud meteors, comets etc but also water for the Moon as well as it would seem the Earth during the period of maximum(sorry about this) “Velikovsky” activity.
That being so, perhaps the moon is a case of development in progress. The Earth contains an abundance of resources. After this discovery perhaps the Moon does too! I’ve always been askance at the attitude that: “Well we’ve been to the moon and there’s not much there!On to Mars!” and felt it was somewhat premature; considering that the explorations made were very cursory, and then only to affirm manned landing viability.
Oddly, the same mindset goes for Mars. We now find that had Viking scooped just a bit deeper, Ice would most likely have been found! Less than 4 years after the last moon mission as well. What a jump start for REAL space exploration – at a time where we had both the money and manpower resources to do something about it!
One really gets a grasp of how negative suspect motivation can be for certain endeavors; not merely in terms of the right hardware for the wrong mission and cancelling everything once the “crisis” is over, but the entire direction of the space program: most especially the manned sector. Clearly the motivation has little to do with Exploration since it’s now clear in Space that machines can do 95% of what is required with a minimum of manned participation: Hubble excepted.
Even so that was actually service and Maintenance. I’m sure most of the Astronauts do not like to be thought of as Space mechanics, but in truth, that’s what they are!
The Gravity Well of Earth being what it is, if we wish to do more in exo-LEO Space then we need a permanent presence there. What better place than a resource-rich abode like the moon with its protective Regolith if we’re prepared to go underground? The moon is superior in most respect than the Langrange points or even LEO as a Space Base both in occupation and Launch terms. If normal and light water are there in useable(but probably @ largely recyclable level) quantities. what else there? We now have prototyping machines which would be ideal for creating an industrial infrastructure without transportation of heavy plant; and what better place than the moon for Fission based and later Fusion based power generation. Then there are Far-Side Astronomical observatories, laboratories…the list is almost endless and I’m sure there are ways to work with local resources so as not to haul hardware up the Earth’s Gravity well. Once we’re fully established, Interplanetary ships/craft can be placed in Lunar Orbit to shuttle between Mars Orbit and Back using Lunar resources rather than the much more expensive one of Earth. Not to mention the saving of some 8 m/s of Delta V, trading mass for Velocity. I say back on the moon by the 50th Anniversary: we can do if we apply ourselves – in any case we have greater resources to work with. Time to cease procrastinating!
Comment by Kit Hildreth — September 28, 2009 @ 5:32 pm
Russell,
Your estimate is as good as any other that I’ve seen. Well done!
Because this volume is spread over a very large area, it may be difficult to mine and extract. We calculated the amount of water possibly present as concentrated ice in the polar dark areas based on a variety of radar about as much water as in the Great Salt Lake.
Comment by Paul D. Spudis — September 28, 2009 @ 6:53 pm
Wow that’s a lot less than my calculations, but I noticed that you are looking at concentrated ice. Thanks for clarifying that for me.
Volume of water in the Great Salt Lake: 0.0189200000 km^3
Comment by Russell — September 28, 2009 @ 8:30 pm
Let’s say that the origin of this water is solar wind reduction of silicates in the existing rocks. We still have solar wind and we still have plenty of (unreduced) rocks on the Moon. If we were to harvest the top layer of the soil, thus exposing a new layer of (unreduced) rocks would these too produce water once the solar wind sweeps across them? Would it effectively be possible to ‘farm’ water this way? Or would the process take much longer than that?
Comment by Anders Feder — September 29, 2009 @ 1:08 pm
Anders,
We just don’t know enough about the water to understand how it’s made and transported. In principle, your idea could work, but we have no idea of how fast this reduction occurs. We’re not even sure that’s the process we’re looking at yet!
Comment by Paul D. Spudis — September 29, 2009 @ 3:59 pm
[...] is an extremely useful substance in space. The recent finding of water on the Moon has generated considerable comment in the space community; a quick search on Google using the [...]
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