Searching for Extraterrestrial Life

I'm reading a book about the possibility of life as we know it (or maybe as we don't know it) on other planets in our solar system and on extrasolar worlds, THE SECRET LIFE OF THE UNIVERSE, by astrobiologist Nathalie A. Cabrol. The author, director of the Carl Sagan Center at the SETI Institute, has worked on multiple unmanned space exploration programs. Reflections on her own experiences in that field lend a lively, personal touch to her in-depth analysis of the subject. Published in 2023, the book contains information about discoveries nearly as up to date as a reader could hope for. This book could serve as a valuable resource for science-fiction writers.

After two introductory chapters about Earth and the origins of living organisms here, she lays out the basic conditions for life as we know it -- mainly a temperature range where liquid water exists, the presence of certain vital elements, and particular levels of gravity and atmospheric pressure. Ideal geological and meteorological conditions also contribute to the probability that life could develop and survive.

Detailed analyses of Venus and Mars explore whether living creatures, if only on the microbial level, could exist there. Other possilities are some of Jupiter's moons and Titan, a moon of Saturn, since organic molecules and liquid water have been discovered on them. More surprisingly, Cabrol proposes possible environments for organic evolution on dwarf planets and even Mercury and our moon. Later chapters plunge into more speculative discussions of life that might exist on planets of other stars. She delves into the Drake equation (how statistically likely are extrasolar biospheres, intelligence, and civilizations?) and the Fermi Paradox (if other advanced civilizations exist in the universe, where is everybody?). Of course, the problem with determining the likelihood of some of the factors involved is that we have a sample of only one, our own world. There's a chapter on the active search for life throughout the galaxy, especially the SETI project. The author also considers the broad question of the definition of life and whether artificial intelligence could qualify.

The book's endnotes direct the reader to the resources the author drew upon. Her treatment of the various topics is so extensive and deep, however, even sometimes getting rather technical with discussions of organic and inorganic chemistry, that anyone wanting to use this work as background for creating alien lifeforms would hardly need to look elsewhere.

Margaret L. Carter

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