Book Review

Book Review – How to find a Habitable Planet.Colin Burgess.

James Kasting is an American geoscientist and a distinguished professor at Penn State University. Kastings was educated at Harvard University and the university of Michigan, where he earned his Ph.d. He has published numerous papers and uses his experience and background as a professor and an environmentalist to write, “How to find a habitable planet.” In this book he discusses the conditions necessary to support life in our universe and solar system. In this book, Kastings does not seem concerned whether or not life actually exists on other worlds, but ‘can it exist?’ seems to be the question asked. Kastings does not mention what he considers to be the definition of life in this book, although that may not be the point he is concerned with. I will assume he considers life to be carbon based, which requires oxygen and water and reproduces, for purposes of this review. Kastings seems to write in gentle disagreement with another book called “Rare Earth” by Ward and Brownlee. While Kastings takes up the optimism Sagan had, regarding exoplanets and extraterrestrial life, Ward and Brownlee suggest a more pessimistic approach, suggesting that variables such as plate tectonics and the stabilization of Earth’s spin axis by the moon, are rare and that ‘these and other cosmic accidents permitted complex life to evolve on Earth, but it is highly unlikely that this same evolutionary pathway would have been followed on any other rocky planet.’ (P. 12).

One certainly needn’t a chemistry background to read this book, just as I do not. I managed to read this book with little knowledge of chemistry and still managed to glean much information from it. Although, the more educated one is, the more they will be able to appreciate it. Those interested in astrobiology and astronomy should definitely enjoy this book, as it discusses how planets are built, habitable zones, conditions for life, telescopes and past-present space based projects, such as Kepler and the James Webb telescope.

As most of us are aware, earth is not at the centre of the universe, nor is it orbited by our sun. Kastings takes this principle and extends it to biological issues, and suggests earth is not so rare and that it is not at the biological centre of our universe either. He cuts right to the chase in the first chapter of this book and says that NASA’s proposed Terrestrial Planet Finder missions are at the heart of his book. He and NASA researchers want to know, “Are there other planets like Earth and, if so, do they support life?”

A well organized book, Kastings begins by introducing the reader to some salient issues in developing a habitable planet and how planets are formed, in chapters 1-2. He then continues, in chapter 3, to discuss environmental issues to discuss the ‘faint young sun paradox’, solar evolution, how the sun converts its hydrogen into helium and how our suns age plays an important factor in life sustaining conditions for its habitable zone, as a function of distance from sun and atmospheric conditions on our respective planet. Chapter 4 is an important one and uses the Earth’s current conditions and history as an analogy for finding a similar planet to our own. Here, the reader will be introduced to different epochs in Earth’s life and climate history. Here Kastings stresses the importance of understanding why O2 is present in Earth’s atmosphere in order to predict if it is or could be, someday, present in the atmospheres of other planets. (P. 71).

Kastings points out that the oxygenic process only happened once on Earth and oxygen is necessary for complex life to occur. (P. 75).

I will not summarize the sub-thesis of each chapter, but will focus on how Kastings wisely uses the principle of analogy in this book to study what we do not have direct access to, in astronomy. He seems to want to respond to the ‘Goldilocks Problem’ as mentioned in chapter 4 and uses two planets which we can relate to, in subsequent chapters–Mars and Venus. He goes on to discuss how Venus Venus, in some ways, is our sister planet, in terms of size, but certainly not temperature. Despite its tremendous heat and current atmosphere he seems to think it could have contained water at some point, while currently at 30ppm of water vapour in its lower atmosphere. On page 103, the reader can quickly gather that he is suggesting Venus as an inductive starting point for discussing habitable zones around our Sun. The model Kastings proposes suggests that Venus should have lost its water over time by a mechanism known as photodissociation and hydrogen escape. Kastings concludes this chapter by saying, “Planets that are located too close to their parent star are likely to lose their water and become uninhabitable.

In Chapter 8, Kastings discusses the Martian climate, which is our other planetary neighbour, except it is a little colder than Venus and is half the diameter of Earth. Here he discusses the existence of water and ice on the Martian surface and suggests while water may have been in abundance n this surface, at one point, and we can tell this by looking at canyons formed on the surface, (P. 126-27). On page 131 he uses the ‘Spokane flood that created the Scablands of eastern Washington near the end of the last ice age,’ and an analogy for how these valleys were formed by water that once flowed on the surface of Mars, in the past, rather than by landslides.

What I consider to be the greatest strength of this entire book is summed up in the previously discussed chapters. While we do not have direct access to possible earth-like candidates, we can inferentially study them by looking in our own backyard, because what the Earth is made up of, is what is found elsewhere in space. Using our own solar system as an inductive starting point for identifying the sufficient conditions for life, and understanding Earth’s current and past climate, we can examine other planets and identify them as possibly habitable now, or as possibly habitable in the distant future, as the planet undergoes necessary evolutionary changes–even if we never make contact with its hypothetical inhabitants. Kastings gives a good overview of operation science and the forensic science that examines the past in light of the present knowns. One book that I would suggest as a follow up to this one is Norman Geisler’s “Origin Science.” Kastings lays out his axioms well and proceeds to speculate on detection of planets and life from well established guidelines.

The weakness in Kastings arguments, and he seems to agree in the final chapter, that his conclusions are not directly testable. We currently lack the funding and technology to really put these ideas to work and to search for life or life sustaining conditions. Another weakness, which the author also admits, is the conditions of the Drake Equation–put forth in the first chapter–are not satisfiable. I do not quite understand this equation, but am certain the more mathematically minded reader will have more to say on this point. In chapter 1 he introduces this equation and in chapter 15 he revisits it after tackling the satisfiability of the variables involved in it.

This book’s strength and weakness is that the arguments are probabilistic. While the author uses well established knowns and proceeds from there, we are still left saying, “Maybe/possibly…” Kastings writes humbly in this book and says that future generations of scientists will likely be the ones to have more answers.

This book was informative, the logic was tight. One needn’t agree with Kastings on his conclusions about exoplanets, or on extraterrestrial life to appreciate his knowledge of astronomy and science, in general. I would suggest anyone read this book who is interested in the subject and needs an introduction, with how well this book was referenced one could follow the goat trails of suggested reading, including the Ward and Brownlee book, which the author respectfully disagrees with. New terms and concepts are italicized and explained, to make sure the serious reader can become well introduced to the subject. The author seems more than qualified to tackle the thesis he takes on and it has forced me to treat the issue of extraterrestrial life less flippantly and more respectfully. To comment more competently on this book would require more insight than a lay-apologist, such as myself, can provide. I think one with a good understanding of calculus, chemistry or biology would really be able to exegete the wealth of information in this book. As a lay-apologist, I simply benefited from learning more about operation science, and how it is used to interpret our past. Learning about planet formation and discovery was important for buttressing my knowledge in the area of science apologetics.

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