This is certainly a book for the aficionado. Commissioned by a government agency – NASA – it could easily have made for dry technical reading. Instead, for anyone fascinated by or fearful for humanity’s history and fate in the stars, this is an enthralling read.

The scope of the book’s coverage is vast. It is specifically the story of how small solar system bodies – comets and asteroids – went from being objects of superstition and myth to being objects of intensive scientific study, entrepreneurial dreams, and, above all, planetary defense.

In delicious detail, especially regarding more recent events, we learn about the many thrilling episodes of recognition of the hazard posed, and, especially, about the many unsung heroes who, with prescience, dedication, and skill, may one day be recognized as the saviors of our species from a catastrophic impact like the one that wiped out the nonavian dinosaurs, or, more broadly, from city-destroying missiles of the astronomical kind. It never ceases to amaze me how much extraordinary work goes on beneath the radar of general public awareness. This book is one window on that phenomenon.

Of course not even a long and detailed volume like this one can cover everything. There are other good books out there addressing the same general topic, and others that could yet be written. One theme that this book certainly takes note of but could nevertheless bear additional scrutiny is the question of who is responsible for planetary defense. One might suppose that the very term “planetary defense” provides the answer: the military.

But one of the peculiar facts about how planetary defense is in fact being carried out is that the DoD, despite having actually spawned the field, has gladly ceded primary responsibility to NASA. Of course this makes sense in terms of the scientific and engineering expertise needed to conduct deep-space operations. However, the mandate of NASA is primarily scientific discovery, whereas planetary defense is “applied” science.

Meanwhile the DoD has been wholly oriented to defense against human (and largely Earth-bound) enemies of the international kind. Even the new Space Force is focused mainly on human-inspired threats from space.

The result is that planetary defense has fallen between two stools. And as the present book makes very clear, this is not a merely academic issue of how to categorize planetary defense (Is it science? Is it defense? Etc.). Very real budgetary decisions have been made and are being made that determine the security of our country and the world in the face of the impact hazard … and often to its detriment.

So, yes, there does need to be conceptual work on how properly to categorize (this cosmic kind of) planetary defense. But then there will also have to be the hard slog of legislating new mandates and changing organizational cultures and mindsets and so on. In the meantime we remain 100% vulnerable to an impact by any object that gives us only a short warning time.