J. Brit. Astron. Assoc., 106, 1, 1996
John Wiley & Sons, 1995. ISBN 0-471-30824-2. Pp xii + 308, £16.99 (hbk).
reviewed by Jonathan Shanklin
It is often said that you cannot judge a book by its cover, but the cover of this book sets the scene for what follows. Subtitled 'The search for the million megaton menace that threatens life on Earth,' the reader can easily deduce that the plot has a foregone conclusion. However this is not a work of fiction; equally it is not a balanced review of our knowledge of objects that may encounter the Earth.
The author is passionate in his belief that extinction from an impacting body is just around the corner, and this passion comes across well in his writing of a well-produced book. I found very few typographical errors; Kelvins reared their ugly head and there are a few other indications that it is intended for an American market. It is a pity that the author uses the old naming scheme for comets, when he acknowledges that he works closely with the CBAT in the search for Earth-crossing comets and asteroids.
What of the science? Steel discusses the various objects that may hit the Earth and identifies the probabilities of each type doing so. Unfortunately he gets a bit carried away and goes on to identify various periodicities in patchy data and concludes that all extinctions are caused by impacts. A more balanced view would be that extinctions have many causes, mostly triggered by environmental stress which includes that caused by impacts, but which must also include natural climate change, tectonic change and competition for habitat amongst others.
More sensationally he suggests that Stonehenge and the Pyramids were built to observe the after effects of the capture of a large comet (the progenitor of the Taurids) into the inner solar system. He thinks that the zodiacal light would have been greatly increased in intensity and that there would have been spectacular annual meteor storms including major airbursts which would decimate large areas of countryside. What evidence is there for this? Very little as yet; the Tunguska fireball occurred at the right time of year, as did impacts on the moon recorded by Apollo seismographs. However just as a layer of iridium provided conclusive proof of a large impact at the end of the Cretaceous period, so must similar layers in Antarctic and Greenland ice-cores. They haven't been found yet, though the measurements are difficult to make.
Herein lies my main criticism of the book. The author presents many ideas and statements as if they were proven fact accepted by the entire scientific community. Readers should be aware that very often this is not the case, and that there are many postulates and fringe ideas mixed in with the solid fact. In addition there are numerous errors, some trivial such as Messier listing 113 objects, some more technical such as suggesting that there was no Leonid storm in 1899 because the period is not exactly 33 years.
Is it worth buying? Undoubtedly yes. It is a thought-provoking read, which shows that observing asteroids, comets and meteors is still a worthwhile pursuit which may lead to our recognising the object with our number on it.
Jonathan Shanklin directs the BAA Comet Section and visited the most recent UK impact site at Glatton near Peterborough in May 1991. Damage that time was restricted to a few broken branches in a hawthorn hedge, but next time, who knows?
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