To A Rocky Moon by Don E. Wilhelms

To a Rocky Moon, written by Don E. Wilhelms, was published in 1993 by the University of Arizona Press. Like Taking Science to the Moon (Beattie, 2001), it covers the scientific components of the Apollo program. Wilhelms worked as a United States Geological Survey (USGS) geologist during this period, focusing on lunar geology. His book is at once a personal memoir discussing his own activities during the program and a broad overview of how scientific knowledge about the moon evolved during the Apollo era. It’s a success on both fronts. Wilhelm’s personality comes through in his often-opinionated narrative, and the well-organized structure of the book gives a clear view of how data and debates shaped our knowledge of lunar geology.

A side note: unlike many of the books discussed on this site, To a Rocky Moon is available for free online. It can be read at the website of the Lunar and Planetary Institute, here.

Wilhelms begins his story in the late 1890s, decades before the invention of the space-faring rocket. Starting with telescopic lunar observations of the USGS’s own Grove Karl Gilbert, he covers the major figures and theories of moon science up through the dawn of the space age. Next, he dedicates chapters to the major unmanned programs that paved the way for Apollo.

Ranger, the first such program, shot probes directly at the moon for planned crash landings, taking photos all the way down. Surveyor then achieved soft landings on the moon. The landers sampled and photographed their immediate surroundings. Lunar Orbiter—which ran concurrently with Surveyor—did what you might have expected based on its name, orbiting the moon and photographing wide swaths of its surface. Wilhelms explains what knowledge was gained by each mission. The central task of the USGS before, during, and after the flights was creating detailed maps of the moon’s surface. As more data came back, these maps improved, until they became good enough to plan the actual manned landings.

Following the robotic missions, Wilhelms dedicates full chapters to Apollos 11 through 17. The book uses a template for each of these chapters. Each begins with a discussion of the training and planning for each mission, including the site selection process. It then goes on to discuss the actual mission itself, covering the words and actions of the astronauts on the surface and in lunar orbit. The chapters then end with a detailed discussion of the scientific takeaway from that mission. The book concludes with extensive back matter, including appendices, detailed source notes, and a selected bibliography. One particularly handy table in the appendices summarizes how well each mission met each of the scientific objectives of the overall lunar geology program.

Wilhelms explains early on that the central issue of lunar geology in contention during the 1960s was whether the moon was “cold” or “hot”—that is, whether its current appearance was due to exterior forces (impacts from comets and asteroids) or internal forces (volcanism and heat from within the moon itself). Indeed, large chunks of the book are dedicated to the back-and-forth over this topic. Various manned and unmanned missions provided evidence, and the result seems to be a mix of hot and cold. Wilhelms argues that the most significant factor was cosmic impacts, with some relatively minor volcanism also having an effect.

The dating of samples from sites on the near side of the moon, including those from Apollo and from the unmanned Soviet sample return missions, made it possible to build a rough timeline of events in the moon’s history. Wilhelms details these clearly. I found this to be one of the most illuminating parts of the book, since it gives a sense of scale to lunar geology. The major maria, or seas, are found to have formed 3+ billion years ago. Two of the most prominent craters on the near side, Copernicus and Tycho, formed about 800 million and 100 million years ago, respectively. Little is known to have happened during that the 2-billion year gap between the formation of the maria and the recent crater impacts. It’s a nearly incomprehensibly long stretch of time. On the moon’s sister world, Earth, that much time was enough for life to evolve from bacteria into sentient beings capable of spaceflight.

Among the book’s strengths is its insightful look into how the process of science works in a unique circumstance. For thousands of years, humanity’s understanding of the moon was achieved through the eye or through telescopes. But over the course of the 1960s, people’s ability to see and study the moon improved in dramatic leaps and bounds. Wilhelms covers how discussions among scientists—ranging from informal chats to major conferences—collected all the new data that was rushing in and converted it into new hypotheses. And as scientists began poring over the data from unmanned missions, committees also determined how best to spend time on the moon’s surface once people got there. The activities of a scant few hours on lunar ground were the result of a decade of painstaking planning.

As I noted above, the fact that Wilhelms features his personal opinions in the book leads to a particularly compelling read, making the book more than a dry history. He’s in favor of the manned exploration of space, rather than simply using robotic landers or rovers. Throughout the book he cites examples of how geologically trained astronauts (and in Jack Schmitt’s case, an actual geologist) were able to provide detailed and scientifically useful descriptions and intelligently choose samples for return to Earth. Additionally, human explorers are able to troubleshoot issues with experiments and other important gear. Wilhelms reminds us of the example of the Apollo 17 astronauts using duct tape and a geology manual to repair their lunar rover’s fender. He freely shares his opinions about individual astronauts too, many of whom he met and worked with during geological training. Dave Scott, he says, was among those who took a keen interest in geology. Alan Shepard found it dull.

At the same time, Wilhelms is blunt in his criticism of other areas of the Apollo program. He criticizes those he believes were doing bad science, in particular calling out Thomas Gold. Gold is best known for his pre-Apollo theory that the first astronauts to land on the moon would sink beneath meters of loose dust. Wilhelms makes it clear that this was a fringe view, and that Gold was hanging onto his peculiar beliefs in spite of the evidence.

Wilhelms also criticizes some aspects of the mission planning, and in particular the selection of the Apollo 12 landing site—he thinks they should have landed near Surveyor 1, rather than Surveyor 3—for not maximizing the possible scientific return. Finally, he criticizes the cancellations of Apollos 18, 19, and 20, for which rockets and spacecraft were already being built. The marginal cost of keeping these missions, he says, would have been relatively minor since the hardware was already paid for.

As you can probably tell from the above, I quite enjoyed To a Rocky Moon. Still, a few aspects of the book make it less accessible than I would have liked. Wilhelms throws a ton of names at you, listing just about everyone who attended a conference, meeting, training session, or other event. This is appreciated for the sake of completeness, but it can be hard to keep track of all these characters at once. Similarly, Wilhelms does not shy away from the use of dense lunar geological terminology—again, the comprehensiveness is to be commended, but it takes some serious concentration to keep up if you’re not already well-versed in geology. Including a bit more explanation of these various terms in context might have made it a slightly easier read.

I mentioned Taking Science to the Moon at the top of this review; that book is an excellent companion to this one. The two titles present much of the same material from different angles, giving the reader a more complete perspective on Apollo science. Beattie comes at it from the engineering side, figuring out how to plan, design, and carry out experiments on the moon. Wilhelms approaches it from the pure science side, taking the results of those experiments and using them to piece together basic facts about lunar geology. The two men actually cross paths in each other’s books; both serve on a committee dealing with the selection of Apollo landing sites. I ended up reading the two books back-to-back, and I highly recommend taking this approach if you are interested in Apollo science.