Worlds Without End: The Exploration of Planets Known and Unknown

This notable addition to the burgeoning galaxy of nonfiction books about extra-solar planets shines brighter than many of its companions--in part because Lewis (Rain of Iron and Ice) is a planetary scientist (at the University of Arizona) well versed in his field. Lewis is a fine teacher, lucid without being didactic: he explains that while there are billions of galaxies, each containing billions of stars, only a few types of stars are candidates for hosting habitable planetary systems, not only because of their size but also due to their life expectancy. Lewis questions the popular assumption that a habitable world need only contain elements, air and water in similar proportions as found on Earth. He hypothesizes that if there were a smaller version of our planet, it would resemble Mars eons ago, with towering mountains but such a low escape velocity that the atmosphere and water would quickly disappear into space. Lewis succeeds in keeping the necessary geological terminology to a comfortable level for general readers, and he explains fairly complex earth-science concepts with admirable clarity. Be forewarned: Lewis doesn't indulge in speculation about where intelligent life may be found. He is more interested in exploring the basic questions that are at the forefront of today's most advanced observatory science. (Dec.)