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At some future time, it is bound to happen. A space rock large enough to trigger a mass extinction like the one that killed the dinosaurs will be on a collision course with Earth. Or a smaller one, like the impactor that caused major devastation in the forested Tunguska region in Siberia in 1908, will threaten a major population center.
Will humans (or our successor species) be able to do anything about those eventualities? According to NASA scientist and author Donald K. Yeomans in his new book, Near-Earth Objects: Finding Them Before They Find Us, the answer is yes.
"If we find them early enough, we now have the technology to deal with them. For example, a massive spacecraft could be directed to purposely run into an Earth-threatening asteroid of modest size and alter its trajectory just enough so that it would no longer threaten Earth. As it turns out, the dinosaurs became extinct because they didn't have a space program."
The image of space-faring dinosaurs may make readers chuckle, but Yeomans' compact and readable book is about serious stuff. As the author puts it, "While Earth impacts by large near-Earth objects are very low probability events, they are of very high consequence."
NASA has recognized the importance of identifying these dangerous objects since at least 1980, when a team led by Berkeley geologist Walter Alvarez and his father, Physics Nobel Laureate Luis Alvarez, published their findings about the dino-dooming impact. But it took nearly two decades before both the technology and funding were in place to begin a systematic search.
NASA is now tracking numerous potentially dangerous Near-Earth Objects (NEOs), and several new ones are discovered monthly. But in these days of fiscal cliffs and austere budgets, the cost and benefits of such searches, including Yeomans' own Near-Earth Object Program, will surely be scrutinized.
That is not to suggest that Yeomans' purpose in writing this book was political. Its main goal is to invite readers to share a topic that is fascinating beyond its practical importance.
Yeomans' early chapters describe the origin of comets and asteroids and their importance as delivery systems for molecules essential to life on Earth. Later chapters discuss discovering and tracking NEOs, space missions to explore and characterize them, and the possibility of a future spacefaring society that mines their resources.
Readers learn how astronomers measure the orbit of an NEO and the difficulty of predicting its future trajectory after a close encounter with Earth. A particularly problematic object is Asteroid (99942) Apophis, discovered on June 19, 2004, by astronomers from a NASA-funded asteroid survey. At first, its computed orbit gave it a one in thirty-seven chance of impact on Friday, April 13, 2029.
Fortunately, pre-discovery images in the Spacewatch data archive soon allowed astronomers to breathe more easily. Still, as Yeomans notes, this "Poster Child of Near-Earth Objects... with a diameter the size of the entire Rose Bowl football stadium will pass within 5 Earth radii of the Earth's surface, briefly appear as a naked-eye object, and dramatically focus the world's attention on a shot across the bow by Mother Nature."
The book's closing chapter discusses what we can do when another NEO is discovered with a significant impact probability. Given uncertainty in our measurements, how do we change its orbit to miss the Earth? Should we try to break it up so that the pieces are less threatening? Can we avoid sending it on a path that makes impacts more likely on future orbits?
Those questions will leave readers persuaded that the impending fiscal cliff may be the least of our worries in the long run.
Physicist Fred Bortz's twenty books for young readers include Collision Course! Cosmic Impacts and Life on Earth and Seven Wonders of Space Technology.