(And Then I Wrote…) In order to let my backlog of “Across the Universe” columns build up a bit, I am republishing a selection of other articles that I have written and published in various places…
A well-known secret of book reviews is that reviews of bad books are lots more fun to write, and read. On the other hand, having been an author myself, I feel bad about scoring points off someone who’s not around to defend themselves. Every book represents a year of some poor author’s life, and it is just as much hard work to write a bad book as a good one.
Well, this one was a doozie. It was also the first book I was ever sent to review, dating from back when I still worked as a professor at Lafayette College, before I joined the Jesuits. My anger was more directed at the major publisher who allowed it to be printed; the author was certainly open to his own opinions. (And he avoided having to invent his own fact by simply ignoring any data.) The review ran in Icarus in 1988.
As with my previous bad review, I am keeping the entire review including the book and author behind the firewall. No need to embarrass them any further. But I will give you the opening paragraph, simply to show off how I could begin to review a serious science book about the origin of the solar system by quoting Thomas Aquinas!
A principle of ancient Greek philosophy, further developed in the Middle Ages by Thomas Aquinas, held that natural reason could, in principle, discover atleast some aspects of the eternal law of God without recourse to divine revelation. A modern variant on this theme might be that a sufficiently clever scientist should, in principle, be able to reproduce the accumulated wisdom of an entire field of science without recourse to the published literature…
[In order to read the rest of this post, you have to be a paid-up member of Sacred Space, and logged in as such!]
The Structure of the Planets. Academic Press Geology Series. By J. W. Elder. Academic Press, London, 1987. 234 pp., $49.50. [Which was a lot of money in 1987!]
A principle of ancient Greek philosophy, further developed in the Middle Ages by Thomas Aquinas, held that natural reason could, in principle, discover at least some aspects of the eternal law of God without recourse to divine revelation. A modern variant on this theme might be that a sufficiently clever scientist should, in principle, be able to reproduce the accumulated wisdom of an entire field of science without recourse to the published literature.
Such seems to be the goal of J. W. Elder’s book, The Structure of the Planets. Dr. Elder, professor emeritus of geology at Manchester, has produced a work which attempts to describe in one consistent, coherent picture the origin and evolution of the planets. He starts with the origin of the solar nebula, outlines from this the formation of the planets, and then describes the subsequent chemical and physical development of the terrestrial planets to the present time.
In essence, he is tackling the questions which have motivated research in planetary science for the last 40 years. In scope, one is reminded of the early work of Urey and Kuiper, and this general scenario is one which has served as a starting point for virtually all discussions of the origin of the planets. However, as Thomas Aquinas noted, “practical reason is concerned with contingent matters . . and consequently, although its general principles are necessarily true, the more we descend to matters of detail the more frequently we encounter defects.”
One immediately becomes suspicious of two circumstances of this book.
First, one wonders how such a theme could be adequately developed in a book only 210 pages long (Urey’s 1952 book is longer, and it was written before there were any data from space).
Second, one notes that the reference list contains only 35 citations. Of these, three are pre-1900, a third of them are pre-Apollo, and only six of his references were published since 1980. Virtually none of them are papers in the planetary science literature.
In his preface, Elder states that he “decided to refer explicitly only to those matters which bear directly on my theme. For students… there are several good textbooks available… for the expert it would be tedious to have to put up with yet another regurgitation of familiar ideas.” In fact, however, one worries that Elder’s knowledge of the literature may not extend beyond general reference books and perhaps a few Scientific American articles. As a result, he has produced a book which describes a peculiar, quirky view of the Solar System.
He begins with a model for the origin of the planets which is reminiscent of Cameron’s giant gaseous protoplanets hypothesis. His argument for this model is summed up in the book’s introductory chapter: “I should like to note immediately the bias of this book towards sub-theme (i) [direct condensation with possible progressive loss of volatiles during the proto-planet stage]. As I shall show, it is possible to account for the existence of large gaseous planets and small stony planets by a single simple mechanism. Sub-theme (ii) [condensation first into very small bodies (dust or planetesimals) which subsequently accumulate into larger bodies] can produce a plausible story for the stony planets, but is then in trouble with the larger gaseous planets (where did all the gas come from?) – I believe this sub-theme fails because of its preoccupation with the stony planets (in any event the bulk of planetary material is gaseous).”
He also uses the cratering history of the Moon to argue against the accretion of the terrestrial planets from smaller rocky particles. He calculates that extrapolating crater records back as a function of time does not yield enough cratering material to account for masses of terrestrial planets. “The cratering rates would need to be 1000 times greater than observed for the whole planet accretion mechanism to be possible. There never was enough particulate material.” [What I didn’t need to mention in the journal where this was published: this idea is totally nuts.]
The rapid accretion of these protoplanets produces, in his model, sufficient heat to drive off the hydrogen and helium from all but the largest of the protoplanets (which thus become the gas giants). Following this planetary gas blow-off, he is left with completely molten cores, of a temperature approximately 3000”K, which eventually cool into the terrestrial planets. The internal heat of the planets today comes primarily from their initial molten state. Radioactivity is negligible, he argues, except to change the boundary conditions, since radioactive materials are concentrated in the crust. “In this work I (somewhat arbitrarily) assume that no more than 10% of present-day net power output from the Earth’s interior is radiogenic.” [What I didn’t need to mention in the journal where this was published: this idea is totally nuts.]
His model predicts that the gas giant planets should complete their formation sometime after the terrestrial planets have been formed. However, he feels the data available on them so far do not warrant further modeling: “even moments of inertia are poorly known… a number of elaborate models have been produced, involving unnecessarily extreme assumptions and which for the foreseeable future cannot be calibrated within the existing data, the simple model of a chemically homogeneous polytropic gas is adequate.” [What I didn’t need to mention in the journal where this was published: this idea is totally nuts.]
The final third of the book describes in detail his model for the interiors of these planets. He concludes that the cores of the terrestrial planets consist of highly compressed iron oxides, with an FeO-depleted, MgO rich mantle. The density differences among the various terrestrial planets are mentioned but never directly addressed, except to suggest that residual volatile material driven off from other protoplanets should tend to drift toward the Sun (and so toward Mercury). From this he predicts a depletion of “higher atomic mass in the outer portions [of the solar nebula]… thus we would expect Mercury to be enriched in FeO, the Moon to be depleted in FeO, and the Jovian moons to be depleted in FeO.” [What I didn’t need to mention in the journal where this was published: this idea is totally nuts.]
His refusal to use the current literature hinders his work in many ways, major and minor. His cosmic abundances, for instance, come from a 1973 textbook which in turn used numbers from the 1960’s that overestimate the iron abundance in the Sun, for reasons (revised oscillator strengths of iron) which have been well known for 20 years.
The debate between a thick nebula (giant protoplanet) versus a thin nebula (Goldreich-Ward style accretion) has been going on since the 1950’s; he does not address the telling arguments of either side. Why are all terrestrial planets closer to Sun than gas-giant planets? Why does the equilibrium condensation curve work, at least to first order, in predicting the densities of the terrestrial planets? (By contrast, each protoplanet ought to have an identical condensation sequence, unaffected by nearness to the Sun.) Why do the masses of the planets vary smoothly with distance from the Sun? [While his idea is totally nuts, it turns out that the nice simple model to explain this that I was hinting at here has been shown to be unable to explain the fact that none of the exoplanet systems we have found since then actually show this variation; so in this case maybe I was totally nuts. It happens.]
He fails to understand the significance of isotope patterns in meteorites. He states, “I do not allow myself to become too excited about these apparent anomalies when I am (we are) still having difficulty in providing mechanisms for such gross features as the occurrence of small stony planets and large gaseous ones.” But his model for the terrestrial planets starting as 3000°K hot lumps of molten rock surrounded by heavy nebular gases does not allow for the presence of atmospheres whose rare gas isotopes mimic adsorbed gases, not cosmic (nebular) abundances. Isotope and trace element geochemistry has put very severe limits on acceptable models for the chemical composition of the Moon and the Earth; he seems unaware of these considerations.
His model for the structure of the planet’s core leaves several unanswered questions. Assuming that his planets are made with cosmic abundances of the nongaseous elements, where has the sulfur gone in these planets? Where is the nickel, for that matter? Why is the outer core liquid? Why is the inner core not liquid? [Another case where I was snidely implying that we had solved those problems. More data since then suggests maybe it isn’t as easy as we thought.]
This book also suffers from unclear figures and confusing notation. Since the concepts and terms are often of the author’s own invention, one can easily get lost trying to follow some of his arguments. For instance, a series of figures in Chapter 6 plots “C” versus “m,” without explaining what either one is. It requires close reading of the text to discover that “m” might mean the MgO mass fraction, or the “extract mass ratio,” or the mantle mass fraction; it’s not clear which. (It turns out he uses the terms “extract” and “mantle” interchangeably, since his model has the mantle formed as the distillate of a molten whole planet.) A similar graph, Fig. 6.4, plots three curves (one of them identified as “m”) on a graph with axes “m” versus some quantity which varies from 0 to 1000, but which is otherwise never identified. In this same chapter, the Greek letter “xi” can be a constant; or the ratio of core to mantle densities; or the moment of inertia of the planet.
It is clear that this book has limited usefulness to the researcher currently active in the field. It ignores everything that has been done in the last 20 years, it addresses none of the specific questions of current interest, and it presents a distorted perspective of the field as a whole. For the same reasons, this book is of no use to students; they would be better served going to one of the “numerous textbooks” Elder mentions (without naming) in his preface.
But does this book have a place at least in a library, as one person’s view on the origin of the planets? After all, the ideas are thought-provoking, if not always convincing. Dr. Elder may prefer his own back-of-the-envelope calculations to more established work in the literature (for such things as the carbon dioxide content of the terrestrial planets, to give one example), but such arguments can be instructive now and then. He does make valid points at times… some modelers do tend to construct elaborate theories for the early Solar System solely to explain one or two odd bits of data; heat sources concentrated in the crust of a planet are not very efficient at heating up a planet’s interior. He does have a competent grasp of physics and chemistry. What seems to be lacking in this book is a solid overview of the data to which they should be applied.
However, one danger of such a book in a library is that an unsuspecting reader might actually mistake this book for one which reflects the current thinking in the field.
I do not fault Dr. Elder too much for producing a book that is, for the most part, useless to other planetary scientists. I suspect he had a good time writing it; frankly, I enjoyed turning the pages to see what new outrage he was about to perpetrate. I do, however, seriously quarrel with Academic Press for publishing this book. At the very least, no editor should have allowed this book to appear with such confusing notation. And there is no excuse for publishing a scientific treatise which does not cite the literature.
The literature hardly represents Gospel truth, but the “marketplace of ideas” does provide our best guide to those ideas that can survive the challenges of new experiments or observations. Being able to create a scheme for the structure of the planets singlehandedly may be possible in theory, but, as modern church teaching says about Aquinas’ “natural law,” it “leaves so much to be discovered by man himself that, without the assistance of some guide or authority, his search would not be very satisfactory.” Or, in the words of Aquinas himself, “The truth is the same for all, but it is not equally known to all.”