How Likely Is Extraterrestrial Life? by J. Woods Halley

Rating: 8/10

Does life exist somewhere else in the Universe? - this is likely to be a question that intrigues everyone. However as long as we've been searching for it, there haven't been any positive signs, although scientists claim that they do at least have the necessary equipment for finding it.

But that leaves us wondering whether or not scientists will find anything and this depends on the main topic of this book: "How Likely Is Extraterrestrial Life?"

One way of determining how likely it is to find a highly-developed extraterrestrial civilization in the Milky Way Galaxy is the Drake equation. That equation takes into account such factors as the likelihood of life developing on a planet and how likely it is that the star has the right properties to be able to support a planetary system and a planet in the habitable zone.

There are several other contributing factors that come into play and this book describes all of those factors in detail and gives the modern values for some of the variables in Drake's equation. So although in the 1960s when the equation was first proposed, a lot of variables weren't known with any kind of certainty - for example astronomers hadn't even found any exoplanets yet, there was an estimation that there could be 1 or up to about a million civilizations in our Galaxy alone, then J. Woods Halley gives a more contemporary angle to it all.

In addition to the main question, it also gives overviews of the various ways that scientists are searching for extraterrestrial life now, or could do it in the future, and where they think might be some life-forms - Europa and Titan for example.

Although the main view in this book is that finding extraterrestrial life is unlikely, then the writing is quite optimistic and informative.

I found the structure of this book to be very good, as it begins by explaining the astronomical factors that come into play first - what sort of star might be suitable, where does the planet have to be located, what conditions there should be and so forth. And after that the book goes into the biological factors -the likelihood of life arising on a suitable planet. To top that off there's discussion of why the search for extraterrestrial life hasn't been successful this far and why it might never be successful.

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