American Scientist

Impact! The Threat of Comets and Asteroids. Gerrit L. Verschuur. 237 pp. Oxford University Press, 1996. $25.

Asteroid: Earth Destroyer or New Frontier? Patricia Barnes-Svarney. 290 pp. Plenum Press, 1996. $25.95.

Mining The Sky: Untold Riches from the Asteroids, Comets, and Planets. John S. Lewis. 256 pp. Addison-Wesley Publishing, 1996. $26.

In 1980, when Luis Alvarez and his colleagues attributed the excess iridium found in the fossil record at the Cretaceous/Tertiary (K/T) boundary to an extraterrestrial impact, they were greeted with the requisite and customary scientific skepticism. Over the years, however, their measurements have been confirmed at different locations, and shocked quartz, soot and residue from massive wildfires above the iridium anomaly have provided additional evidence of impact. After a decade of further research, magnetic, gravimetric, petrographic and isotopic evidence linked an impact crater buried beneath 1,000 meters of sediment off Mexico's Yucatan peninsula with the K/T boundary event.

In their well-written books, Patricia Barnes-Svarney and Gerrit Verschuur present recent scientific findings from NASA's exploration of small bodies. They offer good summaries of our knowledge of asteroids, comets and meteorites, the ways in which we acquire that knowledge, and our current understanding of the formation of the solar system. Adding drama to the story is the very real statistical probability that civilization is poised on the edge of extinction.

Their books differ slightly in emphasis. Verschuur stays within the solar system, tracing theories of its origin back a few centuries. His account piecing together the research that led to acceptance of the Chicxulub crater as the site of the K/T impact 65 million years ago is the first I have read. It is an interesting story—unfolding in the mass media as well as the scientific literature. Verschuur also attends to the predicted climatic consequences of catastrophic impacts in terms of tsunamis and the cratering observed throughout the solar system. In a brief conclusion, he discusses the pros and cons of proposals to use military technology to avoid global catastrophe, and closes with humble and well-expressed reflections on the vulnerability of civilization.

Barnes-Svarney's account of asteroids and comets, their effects on the earth and the techniques used to assess the threat of catastrophic impacts is very readable, thorough and accurate. She places her story in the context of astronomy, walking the reader through the components of the solar system, which she relates to the large-scale structure of the universe. This is not an easy task, and she succeeds moderately well. After reviewing the facts and statistical probability of impacts and developing the catastrophe scenario, she presents the threat as an opportunity, leading the reader to hope that we will have time to use small bodies in space for expanding civilization beyond the earth.

Mining The Sky, by John Lewis, contains much of the same information plus a discussion of the technology required for colonization of space. In this persuasive work, Lewis, an accomplished cosmochemist who is co-director of the NASA/ University of Arizona Space Engineering Research Center, presents his vision for civilization's expansion beyond planet earth. Beginning with the 15th-century Age of Exploration, Lewis reviews simultaneous developments worldwide, on topics ranging from recognition of outer space to rocket propulsion. He reports results from NASA's space exploration, notes the limiting technologies—a lack of effort to develop agriculture in space and the absence of rocketry to get us there—and argues with dogged determination that moving beyond earth will be economically feasible and will expand civilization in terms of the human spirit and its accomplishments. Although his efforts to implement this vision have recently been subjected to the funding ax, the first private company (Pegasus Development Group, Inc.) planning to build and launch a planetary probe has just gone public. Lewis expresses his frustration with the NASA administration, but current events in the private sector parallel his vision.

Trying to create an economic structure for space exploration, Lewis looks beyond the moon to the asteroids and comets for life-sustaining resources. After a tutorial on meteorites, asteroids and comets and an introduction to astronautics, Lewis conducts a cost-benefit analysis of the trip to the asteroids versus their value, which he estimates as equivalent to the gross global product of earth for the next 30,000 years! If I were not acquainted with Lewis, I would probably have put the book down here. Back to astronautics: We continue through the solar system, considering Mars, its moons, and the requirements of getting there and sustaining human activities. The final dream is of bringing back helium-3 from Uranus and selling it for astronomical sums to supply the energy needs of earthlings.

All three books are informative and well illustrated. I would recommend Verschuur and Barnes-Savney's books to anyone who wants to think about and worry about out-of-this-world natural disasters. Impact! had a handful of annoying typographical errors. I found Lewis's combination of fiction, persuasion and economic perspective refreshing. Furthermore, Lewis is not afraid to trace ideas to the writers of science fiction. A poetic or literary prelude to each chapter provides a pleasant introduction to material that might otherwise be quite dry.—Lucy-Ann McFadden, Astronomy, University of Maryland