Fire in the Sky Cosmic Collisions, Killer Asteroids, and the Race to Defend Earth

Can you have too many books on the same topic? Not four months after the publication of Cosmic Impact in February 2019, which I reviewed earlier this year, Scribner books published Fire in the Sky in June. The former book was written by astrophysicist Andrew May, while Gordon L. Dillow is a newspaper reporter and war correspondent, coming at the subject from a different angle. Despite touching on many of the same events and topics, he provides a wealth of new information in what is a thoroughly researched work of popular science. But first, let’s go to Arizona and turn back our clocks some 50,000 years.

As an Arizona resident, it is only logical that Dillow takes Meteor Crater as his starting point. At some 170 metres deep and almost 1200 metres in diameter this impressive astrobleme, or star wound (what a beautiful word he introduces here!), is one of the best-preserved impact sites on our planet. It also plays a large role in the history of impact theory and Dillow skillfully uses it as his jumping-off point for a science history lesson that spins itself out over the first half of the book.

Although Native Americans in the area believed Coon Mountain, as it was known back then, to be an impact structure, the Western academic establishment did not. They were still held in thrall by the geological doctrine of uniformitarianism, which held that changes on Earth happened gradually through known processes (see my review of Cataclysms for more). When the famous geologist Grove Karl Gilbert mounted an expedition to Coon Mountain in 1891 to address the question of its nature, he considered the possibility of meteoric impact but rejected it in favour of a volcanic steam explosion. Not that strange, with the 1883 volcanic eruption of Krakatau still fresh in people’s minds (see Krakatoa). With that, the case was closed for geologists. But it was not for Daniel Moreau Barringer. Nor, later, for Gene Shoemaker.

Where May’s book focuses more on the technical side complete with diagrams – the celestial mechanics of asteroid orbits, the different types of asteroids – Dillow instead largely focuses on the human story of geology’s history. He gives a delightful introduction to early efforts, including the 1800s group calling themselves the Himmelspolizei or Celestial Polic. But the focus is on the fascinating story of both Barringer and Shoemaker. The former made his fortune mining but then wasted it over the next few decades, from 1904 to 1929, digging holes in the crater, obsessed with the idea that there had to be an enormous meteor buried there somewhere. He published academic papers on the topic, but his belligerent attitude made him few friends (see Coon Mountain Controversies). The latter, upon visiting the crater in the 1950s, thought it looked like those left by nuclear bomb tests, just bigger. He changed his career from geology to astronomy, joined NASA, and set up the first observatory to find and track asteroids that could pose a risk to Earth (see Shoemaker by Levy).

A recurrent theme in this book is the reticence of the geological establishment to accept the impact theory (see also Four Revolutions in the Earth Sciences, which covers some of this history in its chapter on impacts). Despite mounting evidence, volcanism remained the preferred explanation for craters both here and on the moon. Dillow traces the big change in attitude to two things. He gives an excellent brief history of the dust kicked up by the famous 1980 Alvarez et al. Science paper that proposed the Cretaceous ended with a bang (see also T. rex and the Crater of Doom and my review of The Ends of the World). And while scientists were busy arguing, Shoemaker discovered an asteroid on a collision course with Jupiter, which it hit in 1994 (see The Great Comet Crash)

From here on outwards Dillow makes clear how the sniggering around the wacky concept of giant-rocks-from-space died down, with the 2013 Chelyabinsk meteor a disconcerting reminder that the threat is real. He describes the many initiatives to find and track Near-Earth Objects or NEOs (see also Near-Earth Objects), and joins astronomer Richard Kowalski at the Catalina Sky Survey to learn how asteroid sightings are shared and verified by amateur astronomers around the world.

Dillow takes the same historical approach when considering what, if anything, we could do. From the 1967 MIT student project, Project Icarus, that asked participants to come up with solutions, to NASA’s 2005 Deep Impact mission that hurled a heavy projectile at a comet, people have been considering all sorts of strategies. NASA now even has a Planetary Defense Coordination Office and Dillow interviews its officer, Lindley Johnson.

There are really only two options to deal with an incoming asteroid: nudging it or nuking it. Dillow briefly considers the slow-push methods that aim to change an asteroid’s course but spends most time on the idea of the kinetic impactor. Basically, the idea of launching a large object or nuclear warhead to blow up the incoming threat. The latter is, unsurprisingly, controversial, and Dillow examines the different opinions on the topic. For now, it might be our only realistic option though. Similarly insightful is his coverage of several “asteroid war games” conducted by NASA and FEMA (the Federal Emergency Management Agency). These are tabletop exercises to train government officials on how to respond when a natural disaster strikes. Obviously, these drills are somewhat different from the regular ones, both in the likely long lead time where we know an impact is imminent years in advance, and the limited capabilities we currently have to actually do something.

Fire in the Sky is an excellent example of an outsider digging into a topic, doing his homework, talking to experts, and becoming fascinated with the story he uncovers. With a reporter’s flair, he transmits his enthusiasm, making this a fun book that treads lightly on the science side of things. His focus on the human history ensures the book does not simply rehash recent publications such as Cosmic Impact. Dillow makes a convincing case that, despite so many other problems here on Earth requiring our attention, we would do well to apportion some of our funds to keeping an eye on the sky.