Viewing the Moon in a new light
Ken Murphy / 3:30 am January 22nd, 2008
“New Views of the Moon”, edited by Bradley L. Joliff, Mark A. Wieczorek, Charles K. Shearer, and Clive R. Neal.
Published in 2006 by the Mineralogical Society of America and the Geochemical Society, it weighs in at a stout 721 pages with index. One spelling error noted, illusive for elusive, and a couple of typesetting errors. Oh, and sometimes sentences will get diverted, as often happens when writing at this level, and never.
This book has it all. Anything you want to know about the rocks on the Moon, you’ll more likely than not find somewhere in here. It can rightfully claim to be the worthy successor to Heiken and Vaniman’s “Lunar Sourcebook” from 1991. While a successor, it’s certainly not a substitute for the Sourcebook, as New Views is sort of the digested end product of the Sourcebook supplemented by the Galileo, Clementine and Lunar Prospector remote sensing data. If you want to get closer to the raw data, Sourcebook is where you want to look. If you want the results of that plus all of the many papers published since then, then New Views is the answer.
These guys were thorough. The Introduction and Overview section alone has a 15 page references section. 18 pages for the second chapter. The bibliography alone makes the book a worthwhile investment for identifying the scores of source papers that have fleshed out our understanding of the Moon. Significant amounts of charts, graphs, illustrations and tables supplement the text. Twelve pages of color plates in the middle cover more false color remote sensing info than I’ve ever seen collected together before. I’m not sure why a Samarium abundance map is important, but it’s in there. I even learned that the J2 portion of the Lunar geoid is 1/3234.93, something that the folks who do the orbital calculations have to contend with.
Like most books about the Moon, we start off with a brief history of how the Moon got to where it is today. Though at 66 pages brevity might not be the predominant factor here. To give you a sense of level of the content, here’s one of the sentences from section 2.3.4 Loading-induced tectonism:
“Schultz and Zuber (1994) investigated faulting caused by axisymmetric surface loading and pointed out that geophysical models of flexural stresses in an elastic lithosphere due to loading typically predict a transition with increased distance from the center from radial thrust faults to strike-slip faults to concentric normal faults.”
Sure, anyone can puzzle it out with time, though it makes for slow but thorough reading. And you do have to be careful and read everything, or you’ll miss stuff like the fact that deep-seated moonquakes seem to originate in particular ‘nests’ in what may be a partially molten core, and correlate with the tides on Earth (presumably as a function of the orbital geometry, which manifests itself in the varying magnitude of the tides).
Next up is ‘Understanding the Lunar Surface and Space-Moon Interactions’. It covers the regolith and samples that we have here on Earth, and then dives into Lunar mineralogy as based on the samples - the silicates, the oxides, the phosphates, and iron metal. It also touches on the importance in Lunar rocks of the magnesium to iron ratio, as apparently the Moon ran out of magnesium first, making the earliest pyroxenes and olivines more magnesian, and the later ones more ferroan. Once the basics of the mineralogy are laid out, we then delve into how they’re put together to form rocks. The Moon may not have as many kinds of rocks as the Earth, but it does have some that the Earth doesn’t have. IIRC we did end up finding Tranquilityite, once we knew what to look for from our Apollo experience, in South Africa. This part is hard-core geological stuff.
As a side note, one overlooked benefit of the Apollo program is that the samples, on a per gram basis, were cheaper than any other sample return mission to date. A group of students (Kronos) participating in the Lunar Moot Corp, perhaps excited by the pictures of meteorites lying on the surface of Mars, decided to look at the business case of returning ‘authentic’ Lunar meteorites (valuable because they could be documented) for sale in the private market. They looked at various sample return missions, from Apollo to Genesis, and calculated the per gram cost of the returned samples. Apollo wasn’t just cheaper, it was way cheaper. The robustness needed to fly the crew gave the margin to carry nearly 400,000 grams of samples back to Earth over the course of the program. Sure, Moon rocks aren’t directly comparable to Solar wind or comet particles, and I doubt there was much transparency into the Soviet Luna program, but still, the results were pretty impressive. I’ll have to see if I can dig up the slides on the net. (Ah, here we go (pdf))
Also explored is the evolution of regolith in the Darwinian environment of micrometeorites and energetic particle interactions, as well as an overview of remote sensing of the composition of the Lunar surface, and a brief look at the tenuous Lunar atmosphere.
Working deeper into the book, we delve deeper into the Moon to learn about the ‘Constitution and Structure of the Lunar Interior’. The Moon is much different from the Earth in being a one-plate planet. The crust is thicker on the far side than on the near side. It’s really thin in parts of the Aitken Basin down near the South Pole. It rapidly gets much more complicated than that. Further down in the mantle we start entering the realm of significant speculation and the work of seismologists attempting to read into the data returned by the rather limited extent of instruments left on the Moon by the Apollo missions. Maybe a robot lander could go visit them and turn them back on? Even more speculative is the nature of the core of the Moon. We know the center of mass is offset from the center of geoid, and that the axial radii are not at perfect right angles to each other and are of different lengths. Mass and moments of inertia are beyond the scope of this review. Some of the macro-measure tools are discussed like laser ranging and free oscillations, and the chapter ends with some of the big unanswered questions (old and new) regarding the overall evolution of the Moon. This chapter had a 20-page reference bibliography.
Once the macro structure is described, we then get into the ‘Thermal and Magmatic Evolution of the Moon’. The general consensus is that the Moon was probably molten early in its life, which allowed the lighter anorthosites to rise like a foam to the top. It crusted over, and as the solidification progressed inwards successively heavier rocks cooled. Mega-Impacts helped to fracture the crust, and from time to time heavy lavas would push to the surface, rich(er) in things like iron and aluminum. When the lavas erupted has an affect on what kinds of elements in which they’ll be enriched, which is important later on in mining and beneficiation. Speaking of which, let’s hustle through the next chapter on Cratering History and Lunar Chronology, which is important, and get to a nice bonus chapter to see in such a thoroughly scientific book.
For business minded folks such as myself, there’s a chapter on ‘Development of the Moon’. Though really, it’s not especially for businessfolks but rather humans developing the Moon to useful ends as part of the expansion of humans into space. It outlines a number of ways in which the Moon can serve as a testbed for technology development with Mars-related applications. It notes energy alternatives such as Solar Power Satellites (now known as Space-Based Solar Power, or SBSP), Lunar Power Systems, and 3He (now only ten years away! [that’s a decades-long inside joke in the fusion field]). It touches on the industrialization of space, and some of the products that could be provided by the resources of the Moon.
Lunar industry is going to require a new mindset, one that looks at an entire value-chain in processing regolith, as opposed to one-off products. Thus, regolith is initially shaken and baked at about 800 degrees to drive off any volatile Solar-Wind Implanted Elements (SWIE). These would be harvested and separated for sale to one set of users. Then the main processing would occur (O2 generation) for multiple sets of users, with the remaining slag then used to create aeroshells for use in LEO or for Mars-bound vehicles, yet another set of users. The value of the SWIEs alone is enormous, given that it is mostly hydrogen, but also helium, nitrogen, etc. The value of the oxygen is important as part of the transport fuel chain in cislunar (between the Earth and the Moon’s orbit) space.
The chapter takes the next step and explores the exploration and development of the Solar system. The key here is fuel provision from the Moon. Oxygen is the obvious first step, because if you can supply it to LEO, then the amount of payload that you’re launching from Earth (as opposed to fuel) to go trans-LEO, like to a geostationary orbit, then goes up considerably. The basic rule is that we want to maximize the amount of high-value-added payload that we have to launch from Earth, and minimize the low-value-added payload like raw oxygen, and even things like high weight heatshields, which could be bolted on in orbit for the return trip. As more infrastructure is emplaced on the grayfields of the Moon, it can start marching up the value chain. PV cells for SBSPs is often mentioned, but even things like titanium struts are possible.
The logical marshalling point for cislunar space is the high ground of the Earth-Moon L-1 point, known as EML-1. Picture a line joining the center of the Moon and the center of the Earth. L-1 is the point on the line where the Moon’s gravity, Earth’s gravity and centrifugal force all balance out and something put into orbit at that point will stay there absent outside forces. The problem is that there are outside forces like the gravities of the Sun and Jupiter, so your best bet is to put your something into what’s called a halo orbit, whose radius is perpendicular to the Earth-Moon line. This lowers the station keeping requirements to tens of meters of seconds of station-keeping, which is really cheap by satellite standards.
When folks talk about launching a trip to Mars from the Moon, they’re really talking about assembling it at EML-1 with high-value-added components (like electronics) brought from Earth, and low-value-added (but high mass) stuff like titanium girders and aluminum plating and raw oxygen coming from the Moon, and everything put together and thoroughly checked over with some test runs around the Moon before heading out on its expedition.
EML-1 also happens to be the cheapest launch point, in terms of change of velocity (which you use the fuel for) requirements, of anywhere in near-Earth space besides the Earth-Sun L-2 (SEL-2) point. It is the on-ramp to what is known as the interplanetary superhighways, a supercheap way to get uncrewed probes around the Solar system. It’s also a great place from which to stage missions to GEO for any number of purposes. It’s a good place to not only look at the Earth and the clutter we’ve thrown up in space around her, but also the Moon, in towards the Sun to look for potential impactors, and out towards the rest of the Solar system and beyond, free of the clutter in cis-GEO space.
Next we visit the Moon as a planetary science laboratory, primarily on a macro scale, and some of the equipment required for a thorough mineralogical search. My personal interest is in the Moon as an impact record. The Earth is ever-changing, and so we’ve really only been able to identify the grossest of insults, the astroblemes that still scar our planet despite her best efforts to erase them. The Moon is different, essentially static and has been for a looong time. Impacts affect the surface in a fairly well understood way, and the affects stay there until disturbed in some way. Crater counting, sizing, and dating through sampling will allow us to develop a much better understanding of the kinds of things that come wandering into Earth’s neighbourhood, and more importantly whether there is any cyclicality in the impact record (since what little we’ve found on Earth seems to point to a 30-35/60-65 million year recurrence in sizable impactors, but we really have too few data points to really know. The Moon is invaluable in this regard and I wish the book had touch on that point in this section.
Astronomy on the Moon is another area to explore, although here the debate is between “grounded” scopes and their limitations, against free-floating instruments in space (Hubble, SOHO, XMM, WMAP, et al), and their limitations. For certain things, the Moon is ideal, but not for others, and so really both types of instruments will have their place in our toolbox. My preference is for the kind of slow, monotonous, boring stuff that you don’t want to waste the orbital scopes on, since someone’s always going to want to use their capabilities to look at a different part of the sky for a Gamma Ray Burst or whatever. Use the Moon scopes to keep an eye out for out-of-plane incoming objects, especially comets, with telescope facilities at each of the poles in ever-dark super-cold craters. While the book does note that the far side of the Moon is effectively radio-silent from the all of the electromagnetic signal that we humans generate here on Earth, it does technically receive a small murmer of Earth-origined signal reflected back from small bodies scattered throughout the Solar system.
A quick discussion on transportation highlights just how crucial this element is in anything we do in space. The Space Cynics like to harp on it, but the fact is we do not have transportation to the Moon right now, and we barely have transportation to orbit, so transport is what everyone needs to focus all of their attention on to the exclusion of everything else. Which is kind of silly, as you have to figure out where you’re going to go and what you’re going to do with the space transport once we do solve the problem.
One thing to do is mine the Moon. The next 24 pages outlines the development and use of Lunar resources, from the compositions of the rocks, including SWIEs and meteorites, to the various distributions that are found on the Moon. A variety of processes are explored regarding the extraction of various useful elements, and even some key strategies for Lunar development. Really Goods Ideas such as Throw Nothing Away - Recycle Everything (i.e. design for recycling).
The last chapter is kind of a summary view from 10,000 feet, exploring the ‘Earth-Moon System, PLanetary Science, and Lessons Learned’. The authors note many of the unique features of the Moon, including a graph of its infamous stabilizing affect on the Earth’s orbital inclination, keeping it close to about 23 degrees as compared with swinging wildly from less than 10 to over 30 degrees (which would make for some horrific weather). Other unique features:
-Moon’s orbit in neither equatorial plane [plane in 3D space which bisects the Earth through the equator] nor in plane of the ecliptic [plane traced by line connecting Earth-Sun]. It is inclined 5.1 degrees to the ecliptic.
-Angular momentum of Earth-Moon system is anomalously high compared with other planets.
-Moon has low density compared with other bodies in inner Solar system
-None of the other inner planets has a ‘real’ Moon of any size. [C’mon, seriously, Phobos and Deimos? They’re not even spheres!]
I would also note that the large size of the Moon relative to the Earth has created a lagrange point right on our front doorstep that connects us with the rest of the Solar system. [By the way, that works for inward-bound as well as outward-bound objects. Comet Shoemaker-Levy that smacked Jupiter is believed to have ridden the gravity warp through the Sun-Jupiter L-2 point for its date with destiny. The one that got the dinosaurs might have snuck in through the Sun-Earth L-2].
The book ends by looking at how Apollo and the Moon have taught us so much more about exploring planetary bodies. Our Moon is, in effect, a Rosetta stone to guide us as we learn to unlock the treasures, in both knowledge and materials, of the Solar system and eventually beyond. It’s going to take a lot of hard work, and a lot of people willing to take risks, to set us on the road to the stars. The Moon is where we’re going to cut our teeth, weaning ourselves from Mother Earth as we journey out of the cradle and into the playground of the Solar system.
So who is a good audience for this book?
-Graduate-level students in Moon studies, maybe Planetary Sciences
-Groups interested in learning what materials there are to work with on the Moon
-Terrestrial Rockhounds who want to one up their brainiac geologist buddies
-Moon-interested activists who want a solid grounding in the facts of the Moon, to rebut ignorant speculation.
-Guys with doctorates
-Mensa folks looking for an interesting diversion
This book is written at the graduate and post-grad level, so don’t have any illusions about drawing value from it if you don’t have a good grounding in chemistry, geology, mineralogy, selenology, and/or all of the above. This one is for the Pros and wannabe Pros (like me!) in field, and for them this book is indispensable as a reference. It fully earned its “Best of the Moon 2006 - Selenology” award, and I consider it the #2 reference in the Selenology section of the Lunar Library, a hairsbreadth so, after “The Lunar Sourcebook” (now in CD-ROM format). Between the two you would have pretty much everything we know about Moon rocks. Now it’s time to go back and start putting them to good use for the benefit of Earth.
A Full Moon very thoroughly at perigee.
