Well written popular science book on the science and history of asteroid and comet impacts on the Earth, detailing some of the basic science and history behind what asteroids and comets are, the surprisingly contentious history of the study of either hitting our planet, the history and science behind famous impact craters and observed impacts, and the debates about what to do with regards to future threats. The author says several times he is not a specialist but it seemed he researched his book very well and kept the writing very approachable for the amateur, particularly with its focus at times on the personalities involved in the field.
The introduction grabbed me right away, the author writing about an asteroid that exploded in the skies over Arizona just before 4 am on June 2, 2016, something the author witnessed, an asteroid that no one had seen coming but that “burst apart in the atmosphere with the energy equivalent of half a kiloton of exploding TNT – that is, a million pounds of TNT…the U.S. military’s most powerful non-nuclear bomb is the GBU-43/B Massive Ordnance Air Blast (MOAB) bomb – the so-called Mother of All Bombs – which has a blast yield of a mere 22,000 pounds of TNT.” This small asteroid “made a MOAB look like a firecracker.”
Chapter 1 focused on the famous Meteor Crater in Arizona, an excellent topic to truly begin the book. The crater, caused by “an asteroid half the size of a city block,” hurtled towards the Earth at 40,000 miles an hour about 50,000 years ago (on a high desert plain near Flagstaff, Arizona). With some good description of what that blast might have been like (including to the unfortunate Pleistocene megafauna that was likely nearby), Dillow did a good job of describing how impressive this event was, noting that the Hiroshima atomic bomb “had the energy equivalent of about twelve thousand tons of exploding TNT…[this] asteroid…release[ed] the energy equivalent of some twelve million tons of TNT, or twelve megatons.” The crater itself is also well described in the chapter from the author’s personal experiences and research, a crater “4,000 feet wide and 550 feet deep, with a flat bottom and steeply sloping walls…as deep as the Washington Monument is tall.”
Chapter 2 was a great introduction to the basics of comets, asteroids, and impacts. A pretty general chapter but a good one, it is one of the few chapters to really discuss comets (with passages on Halley’s Comet and Comet Hale-Bopp), as well as covering the differences between asteroids, bolides, meteors, and meteorites, people actually injured by objects from space (the only one officially known is Ann Hodges, hit and injured by a meteor in Sylacauga, Alabama in 1954, though there are unconfirmed deaths throughout history attributed to impacts and explosions, briefly mentioned in the text), the history of the discovery and science of asteroids, asteroid composition and distribution, how close many asteroids come in terms of near misses (often these asteroids are only spotted after they just missed), and the overall likelihood of asteroids hitting the Earth (over time a certainty basically).
Chapter 3 returned to the Meteor Crater, this time the focus on the history of the study of the crater and the personalities involved as well as the influence all of this had on the science of asteroids and asteroid impacts. Far and away the dominant figure in this chapter is Daniel Moreau Barringer, the man most connected with the human history of the crater, Dillow providing an absorbing biography of this intense personality, a man who ruined himself trying to make a fortune off the asteroid he believed buried in the crater and who tirelessly crusaded to have the scientific world accept the crater was not volcanic in origin. Other personalities figure in the chapter, including noted late 19th, early 20th century American scientist Grove Karl Gilbert (a figure of enormous importance in the history of geology especially in the United States) and Forest Ray Moulton (expert on celestial mechanics, a man whose work showed that most of “Barringer’s asteroid had been shattered or melted into billions of tiny pieces that were ejected from the crater and then had blown away with the wind”). The chapter closes out with coverage of current plans for attempts to mine asteroids out in space as well as spacecraft missions sent to study asteroids related to this (or otherwise studying the content of asteroids).
Chapter 4 was one of the best chapters in the book, focusing at first on the famed Tunguska Event in Russia in 1908, using that as segue into the study of the science of asteroid and comet impacts, recognizing them for what they are, how common they are in Earth’s history, and the long and contentious debate about whether they even existed. Beginning with the lead scientist studying the Tunguska Event, mineralogist Leonid Alekseyevich Kulik (who lead an interesting life), and going on to discuss among other people involved in the location and study of impact craters Englishman Harry St. John B. Philby (father of Soviet spy Kim Philby), Grove Karl Gilbert once again, American pilot and geologist Robert S. Dietz (who coined the term astroblemes for impact crater, a concept discussed in the chapter), and closing with a lot of time spent on another larger than life scientist, a man fascinating to read about and absolutely essential to know about in any discussion on impact craters, American geologist Gene Shoemaker (a man who brought knowledge of the effects of nuclear weapon tests to the study of impact craters on Earth and later the Moon, as Shoemaker worked with NASA in both unmanned lunar missions and the Apollo missions).
Chapter 5 was on a favorite topic of mine, the science and the history of the science on the celestial impact that likely killed the dinosaurs and brought the Mesozoic Era to a close. The two dominant figures in this chapter are geologist Walter Alvarez and his Nobel-prize winning physicist father Luis Alvarez, two figures I know from my amateur readings on geology and especially paleontology (though this author did mention in passing the interesting life of Luis Alvarez, who among other things was on the Manhattan Project, flew in an observer B-29 accompanying the Enola Gay when it bombed Hiroshima, and served on a CIA-sponsored UFO investigative group called the Robertson Panel in the early 1950s; I need to read more on this man). Lots of great science in this chapter too, not just human history, discussing at length the 6-mile-wide asteroid that hit the Earth 65 million years ago, hitting with the equivalent of 100 million megatons of TNT or ten billion Hiroshima bombs and also the science and history associated with the Shoemaker-Levy 9 impact on Jupiter in July 1994 (an event that was an important turning point in how seriously people viewed impacts as a threat to life on Earth) and closing with discussion of various programs to search for potentially dangerous comets and asteroids.
Chapter 6 focused on the hunt for asteroids today that might hit the Earth, especially NEOs – Near-Earth Objects – the author showing an asteroid hunter at work (Richard Kowalski, a professional asteroid hunter who rose up from amateur ranks). Doing a great job (it seems to me) of conveying how asteroids especially are discovered, studied, their orbits plotted and risk of their impact assessed, the chapter introduced still more science in an easily accessible way, including the hazard rating for asteroids called the Torino Scale (a scale that addresses both the likelihood of an asteroid or comet hitting and also how dangerous that impact would be, with 0 being virtually no chance of an impact in the next century and a 10 being a 100% chance for a global catastrophe that could threaten civilization as we know it, one it seems thought probably only occurring every 100,000 years or less often than that).
Chapter 7 discussed at length another wake up call in the field (and politics especially) of asteroid and comet impacts, the February 15, 2013 explosion of the Chelyabinsk meteor in Russia, ironically the same day as a publicized near miss by asteroid 367943 Duende, discovered in 2012 and predicted to pass within 17,000 miles of Earth, closer than many geosynchronous communications satellites (an event in the press massively overshadowed by the Chelyabinsk meteor though prior to what happened in Russia was much publicized). In addition to a lot of coverage of what happened in Chelyabinsk, the chapter extensively covered issues in getting anyone to do anything about planetary defense and the debates swirling around it, along with a profile of NASA’s first Planetary Defense Officer, Lindley Johnson.
Chapter 8 was engagingly written with a storyteller’s flair, focusing primarily on a student war games study to stop an asteroid, Project Icarus, an MIT project in 1967, the author using this as a segue to discuss the technical, scientific, budgetary, and political challenges to dealing with impacts, such as when to act (what probability of impact requires attention and when to act), the different ways of dealing with a protentional impactor (changing the path of an asteroid versus trying to destroy one, nuclear versus nonnuclear options, how much time the different strategies require, how much knowledge of asteroid composition is required, how different tactics might be required for different sized objects or when the threat is either diagnosed or the will to act upon it finally exists).
Chapter 9 read like fiction (this is praise), describing a hypothetical impact by asteroid 2014 TTX, of the events that would enfold relating to its discovery, the prediction of how likely an impact is, predicting where it will impact once impact chances become a certainty, responses to destroy or deflect the asteroid, and what happens with governments, businesses, the economy, and people on the ground. All fiction, but also a real war gaming scenario ran by various agencies and organizations to try to get an idea of what would happen. It raised some interesting issues, such as some techniques used to change the area of impact might shift the area endangered (such as say moving the impact zone from one country to another) and also of the careful use of language in discussing Earth defense programs (don’t say nukes or nuclear weapons, say atomic deflection devices or even better ADDs).
The book closes with a brief epilogue, acknowledgments, some very readable “chapter notes, sources, and relevant fun facts,” and an index. Also included is a section of black and white and color plates.