Worlds Without End: The Exploration of Planets Known and Unknown

I like this book about planets, which is written by an expert. John Lewis makes the point that Earth's history was modified rather dramatically by an impact with a huge (maybe Mars-sized) bolide. That impact influenced the Earth's spin, axial tilt, and internal composition. And it produced the Moon (which was initially far closer to the Earth than it now is). He asks what the Earth would be like had this impact not occurred, but he also explains that this is a very hard question to answer. The author then discusses what the Earth might be like were it a little larger or a little smaller. He shows why a Mars-sized Earth could have taller mountains, due to the lower gravity. And such a planet would be far less likely to have subduction zones, because its lithosphere would be thicker, colder, and more rigid. Meanwhile, an "Earth" with twice the radius would probably be completely covered by water. Next, Lewis tells about giant planets, including ones orbiting other stars. And brown dwarfs. And then he talks about planet-sized moons of giant planets. There's even a nice discussion of spin-orbit resonances. Of course, the conditions on a planet depend enormously on the nature of the star it orbits. For a star to be able to stay on the Main Sequence for a billion years or more, it must be smaller than the O-stars, B-stars, and many of the A-stars: it must be an A7 or smaller. That means F-stars, G-stars (such as the sun), K-stars, and M-stars. Even the small, long-lived, and numerous M-stars (down to M7) could be hosts of planets with Earthlike temperatures. Lewis does ask the question, "how common are planets that are inhabitable by life that is similar to Earth life?" And he indicates that there may be quite a few such planets. I recommend this book, and I enjoyed the style in which it is written.

John Lewis is a professor of planetary sciences at the University of Arizona. Astronomy is the broad field under which this falls, but there is a specialisation within the field. I must confess I have always been one who is more interested in large-scale structures (galactic astronomy), origins and endings (cosmology and the like) as well as `how things work', the theoretical physics aspect. Planetary science didn't really enthrall me as much, even with the increasing availability of stunning photographs and records coming back from the other planets in our solar system. Don't get me wrong - I was fascinating and interested, but it did take a backseat to the other study.This changed somewhat such that planetary sciences became near to an equal footing when instrumentation and measurement became sufficiently precise to begin detecting planets around other stars. Suddenly there was a new universe opening up around each and every star, at least it seemed so for a time. We've reached the point now where announcement of new planets around other stars not only no longer makes headlines, but may no longer warrant a mention in the press beyond the professional journals. Lewis' book, `Worlds Without End: The Exploration of Planets Known and Unknown' helped to fill a gap in my knowledge about the direction and breadth of the new planetary studies. Published back in 1998, it is already somewhat out of date given the speed with which discoveries are occurring in this field, but it still serves as a great, accessible and interesting primer to the study of planets both `at home' and `abroad'. Lewis explores the different kinds of planets, from rocky types like Mercury to the big gaseous giants like Jupiter and Saturn. This survey includes the study of satellites, or planets around planets, as Lewis terms them. There are more moons around Jupiter and Saturn than planets around the Sun (if one does not include asteroids). These make for fascinating trips, too.It is no surprise that these types of giant planets were the first to be discovered around other planets. He talks about the different kinds environments for stars, and in so doing gives a short course on other aspects of general astronomy such as overall galactic motion, the different types of stars and their life cycles, and the different kinds of groupings of stars. For example, a planet around a star in a globular cluster, clumps of stars that exist surrounding some galaxies but to a certain extent separate from those galaxies (rather like gated communities might be to larger urban settings), would have spectacularly starry nights, even if the stars in the cluster were relatively small, and the close fly-bys of other stars would be a million times more frequent, such that the environment of the planet would constantly be shifting dramatically as the orbit would constantly change - stars may even `steal' planets away from one another!Lewis in his final chapter sets the stage for ongoing pla

This is a really good book. Lewis explores the physics and chemistry of the worlds in our solar system, and then using the principles of physics and chemistry learned there to explore the possibilities of other worlds, and life on them.He presents several mind-bending -- yet scientifically feasible -- worlds for our consideration. "Earthissimo," for example, made me put the book down, lean back in my chair, and SAVOR the elegance of the science for several minutes. Wonderful!BUT, like Lewis's otherwise excellent _Mining the Sky_, he doesn't include any graphs, table or illustrations. (He has a few artistic rendering in the middle, which are different.)A few graphs or tables would have clarified his arguments and saved pages of dense, descriptive text.Good book, mind-twisting science, poor presentation: 4 stars.

______________________________________________ Besides being a fine primer on modern planetary science, Worlds without End strikes me as an exceptional resource for science-fiction worldbuilders -- and readers. I've read a couple of world-building books and they were pretty dry. This is the real thing -- a respected planetary scientist (Codirector of the Space Engineering Research Center at the University of Arizona) reporting on recent discoveries of extrasolar planets, and speculating on the range of possible planets that might host life. Lewis does a nice run-through of possible planetary surface chemistries for "life as we don't know it", and reluctantly concludes that extraterrestrial life will most likely be carbon-based and use water as a solvent, because both are the best available by far. Which isn't to say that we won't find some very odd critters out there... And I don't mean to imply that general readers won't enjoy Worlds without End -- I recommend it to anyone who's curious about how solar-systems form. This is a better-written book than his Mining the Sky (1996), though Lewis still gets annoyingly cutesy at times. Anyway, it's almost always a pleasure to read a pop-sci book written by a working scientist. I'm looking forward to Lewis's next. Happy reading-- Pete Tillman Consulting Geologist, Tucson & Santa Fe (USA)

Dr. Lewis starts a scientific inquiry with a humanistic approach--an interesting history and evolution of thought concerning the number of other planets in the universe and whether they host life. The book then discusses the necessary elements for life as we understand it and the prospect of life on other planets, in its likely varieties.This is a successful presentation of these ideas, done in a reasoned and interesting manner. Dr. Lewis' expertise as a planetary scientist qualifies him as an academic, while his wit and readability qualify him as an author.This book is an excellent treatise and exploration of other worlds: fact- and analysis-filled for the techinical among us, yet readable and entertaining for the less so. As such, I recommend the book for all.