The hypothesis: In the shadows of deep craters that pock the south pole of the Moon there might be ever-frozen water.
The experiment: Guide the final stages of the Lunar Crater Observation and Sensing Satellite (LCROSS) rocket into one of the craters and crash it into the surface, hopefully sending a plume of dust into the air that could be analyzed.
The event: On October 9, 2009 the LCROSS Centaur rocket crashed into the crater Cabeus, followed by the LCROSS package itself, which recorded (mostly by spectroscopy) information from the impact plume.
The first results: Just one month after impact, scientists announced that LCROSS did indeed find water. [SciTechStory: On the Moon or elsewhere: Follow the water]
The published results (some presented October 21, 2010 at a joint news conference): Yes, there is more water on the Moon than originally suspected. (Most scientists thought the Moon to be one of the driest places known to man.) In fact, substantial frozen water can be found in locations other than the bottom of deep craters. This is a piece of deduction that comes as something of a surprise. It follows from the measurements of temperatures in the area of the Moon’s south pole. They are the coldest ever directly measured in the solar system. One location registered 27 degrees Kelvin (-246 Centigrade, -411 Fahrenheit), that’s 27 degrees above absolute zero, the point at which atoms no longer move. At 100 degrees Kelvin water is not only frozen but will remain inert for billions of years. In fact, at 100 Kelvin many ‘volatiles’ such as hydrogen, methanol, ammonia, and carbon dioxide will also remain permanently frozen. Scientists believe temperature this cold exists not only in the shadows of craters, but also in the subsurface around the Moon’s south pole, in the lunar permafrost. There may be significant water in the soil even in areas that receive some direct sunlight. This could be up to 30% of the area around the pole.
This is a good thing. Working in somewhat warmer sunlight to extract water, hydrogen, and other substances from the soil of this area could make expeditions, settlement, and eventually commercial utilization possible. If you think about it, how well would machinery work at 100 Kelvin? (If it would work at all.)
For science, the treasure is in the preservation of materials that have been on the Moon – unaltered – for a billion years or more. The spectrographic analyses reveal the presence of many kinds of molecules, including those of hydrogen, oxygen, carbon, and nitrogen – the building blocks of life. The layers of material present the geological history of the Moon, perhaps all the way back to the days when it was still volcanically active.
However, there is the problem of fluff. Literally, the ‘soil’ of the crater is fluffy (‘light’, ‘airy’) in the extreme – so fluffy it could swallow astronauts and equipment far worse than quicksand. Is all the soil around the south pole like that? Probably not, but that’s unknown. As reported by Emily Lakdawalla at the press conference this problem was only partially addressed:
One questioner asked how easy it would be to get water out of the material that LCROSS crashed into. [Anthony] Colaprete answered, demurring a bit, saying that other people had thought much more about this problem than he or the other lunar scientists had. But he pointed out that the fluffy material is much easier to deal with than digging into solidly frozen ground; “you just scoop it up.” You can even just warm the surface, he said — the crater was steaming, and all you need to do is cover an area, then warm it up, to release the water.
However, in my conversation with Pete [Schultz] later, I learned that this ease of accessing the water cuts both ways. I asked Pete what would happen if you stuck a shovel into an area of the type that [Igor] Mitrofanov was talking about, a place that is not permanently shadowed, where there is ice-bearing material a few centimeters below the surface. Pete said, first of all, that despite all the results shown today we don’t really know what things look like much below the surface; all the material that got lofted upward was likely from pretty close to the surface, and the higher things went, the closer it was to the surface when it started. It could be a veneer of material, but we don’t know if it’s a veneer or not. It’s quite possible that it goes very, very deep, and if so, it could be very, very old — possibly old enough for these deposits to preserve volcanic gases left over from the later stages of the Moon’s geologic activity. Secondly, he said, this material is probably so delicate, that even sticking a shovel into the ground might warm it enough to make the water and other, even more volatile stuff (like molecular hydrogen and ammonia) go away — just the shovel will warm it up.
[Source: Planetary Society Blog]
I encourage everyone to read Emily Lakdawalla’s Planetary Society blog entry, LCROSS finds lots of water in accessible places at the Moon’s south pole – but we’ll have to tread carefully. It’s a fine piece of science writing that exposes the texture of real scientific enquiry and her infectious enthusiasm for the field. (She was a NASA deputy project manager and holds a master’s degree in geology.)
As you can see, the published results are far richer than the immediate results. In fact, they reveal a much more complex picture of conditions at the Moon’s south pole. Yes there is water, probably in quantities significant for human activity. There’s a lot more, a veritable treasure trove of materials including silver, manganese, and other ‘resources’ that humans like to grab. However, the environment is more difficult (some would say hostile) than expected. The scientists who made the reports are excited by what they found, but they’re also sanguine about accessibility. There is always the problem of something costing more to extract – especially in energy – than it is worth.