Paul Murdin. Are We Being Watched? The Search for Life in the Cosmos. Thames and Hudson, 2013.

This is one of a number of recent books which have combined astronomy with biology in order to discuss the prospects of finding evidence of extraterrestrial life. This study is, not surprisingly, called astrobiology. The main problem with astrobiology, as the author admits, is that it is "a science about something that might exist, not something that exists for certain". This lack of convincing evidence perhaps inevitably leads the author to resort to padding out his treatment of the subject to produce a book rather than a pamphlet.

Evidence for the possibility of extraterrestrial life has become available only fairly recently. It was not until 1992 that radio astronomer Aleksander Wolszczan, when timing a rapidly rotating pulsar, noticed unusual features which led to the conclusion that there were three planets orbiting it. Many other stars with planetary systems have since been discovered and the increasing use of computers has enabled the process to become at least partly automatic.

Further evidence comes from organic compounds found in meteorites. Thousands of complex organic compounds were found in samples of the meteorite which broke up over Murchison, near Melbourne, Australia, in 1969. Study of these compounds caused controversy as the organic compounds formed by non-biological processes are 'racemic', which means that they consist of equal numbers of left-handed and right-handed molecules, unlike those formed in living organisms which are left-handed, with few exceptions. The amino acids in the Murchison meteorite proved to be predominately left-handed.

A chapter is devoted to the experiments to look for signs of life on Mars. As in other observations and experiments the evidence obtained is inconclusive and the interpretations of it are highly controversial. Of course no one expected Martians as depicted in science fiction stories, but it was thought that it was possible that micro-organisms might live in the soil.

Two main methods have been used to investigate this possibility. The first was the experiments carried out by the Viking landers of 1976 which produced results indicating either the presence or absence of living organisms, depending on which scientists you asked. The second, and cheaper, method was to examine meteorites which came from Mars. This resulted in the discovery, in a meteorite found in Antarctica in 1984, of a microscopic tube-like structure which either is or is not the fossil of a Martian micro-organism, again depending on which scientist you ask.

Apart from Mars, Murdin considers the possibility of life on one of Jupiter's satellites, Europa, as it is apparently covered by an ocean with a layer of ice on top. There has been much speculation about possible forms of life in this ocean, but at present no way of finding any hard facts.

Very little of the scientific speculation in this book is about the possibility of intelligent life, as consideration is given only to listening for alien radio signals from distant star systems. Only a very few anomalous signals have been reported and these have either never been repeated or have no independent confirmation. There is nothing about the possibility of alien space probes lurking in our solar system, or the search for large-scale engineering projects in other star systems, such as Dyson spheres. Some of these ideas have been discussed by serious scientists and engineers, yet Murdin ignores them but finds space for a few paragraphs about Roswell, which, not surprisingly, does not impress him at all. Then why mention it?

This is a book with few surprises for readers interested in the possibility of alien life, as they will already be familiar with most of the main facts and theories. A shorter version, with irrelevant or obvious material excised, might be a good idea for any future edition. -- John Harney

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