Planetary surface processes


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Planetary surface processes, H. Jay Melosh . Purdue University, Indiana Hardback : Series: Cambridge Planetary Science (No. 13) , 2011 , Hardcover , 520 p . ISBN:9780521514187 , 141 b/w illus. 28 tables 34 exercises .

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We live in a Golden Age of planetary surface science. Starting with Mars Global Surveyor and continuing with the remarkably crisp imagery of HiRISE, we now have orders of magnitude more data on the processes occurring on the surface of Mars than we did just two decades ago. The same can be said for Titan and Io. Correctly interpreting these multispectral, hyperspectral, and elevation data sets in terms of the processes occurring on these solar system bodies requires a solid foundation in Earth surface processes (where field work and geochronology are possible) as well as a deep understanding of how different atmospheres, gravitational fields, etc., control differences in the evolution of topography and regolith on different planetary bodies. Few people (if any, besides H. Jay Melosh) have the depth of understanding of both Earth and extraterrestrial surface processes required to do the subject of planetary surface processes justice. Luckily, Melosh has devoted himself to the task of writing a textbook on this subject. Melosh is an intellectual giant, having contributed sufficiently fundamental insights on the evolution of planetary surfaces to be inducted into the National Academy of Sciences in 2003. The result is a peerless book: Planetary surface processes (Cambridge University Press, 2011). The best textbooks accurately describe the state of knowledge, but also inspire students by pointing out curious mysteries we still do not understand. Melosh’s book is informative and inspiring in equal parts.

After an initial tour of the planets, the book focuses on the processes that control the overall shape of planets, from the zeroth-order controls on the diameter of planets to the higher order topographic variations of continents and mountains. Discussions of shape naturally lead to treatments of lithospheric strength, rock creep, tectonism, and volcanism. These subjects are also ably presented in Turcotte and Schubert’s Geodynamics, but the comparative planetary perspective that Melosh provides is invaluable for a planetary sciences student. In what geomorphology or geodynamics textbook can one learn about Triton’s “boiled cantaloupe lands”? Moreover, Melosh covers the material as someone who has thought deeply about which concepts tend to trip students up (students including me, Professor Pelletier, who had more than a few misconceptions cleared up by Melosh’s clear exposition), and his writing is peppered with helpful explanations that foresee the difficulty that students will have with certain concepts. The book continues with a lucid presentation of impact cratering and the evolution of planetary regolith, subjects that Melosh is perhaps best known for in his research. The final chapters cover sediment transport by gravity, wind, liquid water, and ice in a manner similar to those of most geomorphology textbooks, but rich with planetary examples.

This is one of those books, like Turcotte and Schubert’s Geodynamics, that will continue to reward the reader for decades to come. Each time I open this book, I learn something new or at least see an old idea presented in a way I had not thought of before. The only possible quibble one could make about the book is that it does not show students enough detail, via worked case studies, about how to “do” science (i.e., solve specific equations in specific contexts). Turcotte and Schubert’s Geodynamics, for example, has many examples for each type of phenomenon (heat flow, flexure, flow in porous media, etc.), whereas Melosh’s book focuses more on the basic concepts and equations as opposed to their application. To the extent that it is generally best to learn by doing, the book might have been improved with some more worked examples of specific applications. That said, Melosh’s book is more readable than Turcotte and Schubert, a point driven home in Melosh’s preface, where he states that stories (about the history of ideas and the people who created them) are important aids of learning. His book is indeed sprinkled with fascinating stories about the history of science that readers of all levels will appreciate. Another possible quibble is that chapters on sediment transport by gravity, wind, liquid water, and ice, may be covered as well or better in recent geomorphology textbooks (e.g., Anderson and Anderson’s Geomorphology: The mechanics and chemistry of landscapes (2010) (Melosh’s treatment of these subjects is a bit dated). These are minor quibbles, however. The book is a remarkable resource, and I plan to incorporate it in my own teaching of Earth and planetary surface processes, along with excerpts from Turcotte and Schubert’s Geodynamics, Anderson and Anderson’s Geomorphology: The mechanics and chemistry of landscapes (2010), and my own Quantitative modeling of earth surface processes (2008) (all Cambridge University Press).