Rogue Asteroids and Doomsday Comets: The Search for the Million Megaton Menace That Threatens Life on Earth

Related titles include "Night Comes to the Cretaceous" by James Lawrence Powell and "T Rex and the Crater of Doom" by Walter Alvarez.
December 18, 2000

Ever since the first pictures of other planets and in particular their moons arrived, studies have been made of their cratering records. Pictures from space have also been the main method of detecting craters but this time down on earth where plate tectonics, erosion, sediments or vegetation tend to erase them.

Astronomy and Geology linked up when cosmic impact events were suggested as possible cause or trigger for some of the major extinctions we find in the fossil record. The effects of both solar and cosmic cycles on all aspects of life on the planet are now widely studied.

Mr. Steel gives an account of a very bright meteor seen by many people in 1993 in New South Wales. When asked for an estimate of how soon it would before another such sighting to occur the answer was given in years. One week later, however, an object estimated to be 2-3 meters in size and traveling at 30Km/Sec exploded 18Km overhead with the amount of energy produced by a Hiroshima Bomb. Events such as these and the trail of impacts left on Jupiter show that objects in space are certainly not solitary. Lines of craters have been found on other moons in the system. Comet Hale/Bopp provided a spectacular sight a few months ago but for now the interest is in the debris and dust they and asteroids can leave behind often in highly eccentric trails across our orbit. Gravitational forces and solar wind affect the objects and the trails have a structure and it is the "busy" parts of the belt which give the peaks to meteor showers as we pass. The widely varying time scales which have been linked with extinctions and other cycles are the result of earth and solar system moving round the galaxy.

The possible effects of a large impact, global warming, ice ages, large fire storms or basalt floods have all been discussed elsewhere but the book considers several other theories. A large object landing in the ocean could cause a truly instant catastrophe.

This is the tsunami wave which can be caused by earthquakes or large undersea slope collapse. Islands in the middle of the Pacific can feel the effects of activity right across the ocean. The sloping continental shelves amplify the height of the waves and in low lying areas they can reach well in land. Observations of the cratering pattern on Mercury led to one theory where the shock waves from a large impact travel round the globe and fracture the crust on the opposite side. Reconstruction of the continents at the times of suggested impact events seems to make it possible to link basalt floods such as the Deccan traps with their "opposite" partner.

The remainder of the book deals with the problems involved first in detecting objects which may be a threat to the earth and also discusses what or how anything could be done about it. The pictures of S/L 9 described as a "string of pearls" as it approached Jupiter show just how much of a problem this could prove. For a book found

on the astronomy shelves in the library this one provided a very interesting read and shows that we on earth are not alone in space.
October 15, 1998