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What If the Earth Had Two Moons?: And Nine Other Thought-Provoking Speculations on the Solar System

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What if the Earth Had Two Moons?: and Nine other Thought-Provoking Speculations on the Solar System by Neil F. Comins is one of the more interesting books I've read so far in 2010. As an amateur astronomer a few of the questions covered by Comin's wondering imagination aren't new. What is new, at least for me, is his ability to logically work through to a sensible conclusion. Given the range of possibilities covered in What if the Earth Had Two Moons the reader gets a glimpse of an active imagination in operation.

Specifically, the questions asked and answered are:

What if the Earth had two Moons?
What if the Earth were the moon of a massive planet?
What if the Earth orbited a less massive sun?
What if the Earth had a thicker crust?
What if the Moon orbited the Earth in the opposite direction?
What if the Earth had two Suns?
What if the Earth had a twin orbiting on the opposite side of the Sun?
What if the Andromeda Galaxy collides with the Milky Way? (Apparently this one is really going to happen at some distant point in the future.)
What if the Earth formed closer to the center of our galaxy?
What if the Earth formed in the distant future?

What if the Earth had Two Moons is certainly entertaining and quite educational.

If you're curious about any of these questions or just have a love of our physical environment then you'll want to read What if the Earth Had Two Moons.

I highly recommend.

Peace to all.

This is an excellent book! Very well written - I can't set it down. This is one of the most unique, interesting, and valuable books I have read in astronomy and geology. Many deep insights are gained simultaneously by asking "What If?".

Just as an example from the first few chapters, we take our tides for granted. Most of us know tides are related to the Moon, but we might not think the effects are significant enough to understand the topic in any detail. This book shows that nothing could be further from the truth. The effects are significant, and could have been very different for the different moons considered in this book. Only by considering a variety of possible moons (and different home planets) can we really appreciate our tides and what they could have been. You'll understand how our own tides have slowed down Earth's rotation and flung the Moon into a farther orbit. You'll understand how different conditions could have lead to stopping the Earth's rotation and a moon that gets torn apart by Earth and rains down debris to the planet's surface. That could have been us!

But, this book sheds light on a lot more than tides. By considering different possible earths and moons, we can also appreciate volcanoes - the ones we have, and the ones we're lucky we don't. Tremendous insight is gained by this approach, and leaves the reader in awe at - you guessed it - the world we live in, and what it might have been. Many core pieces of our past and present are woven together and elucidated in this book: the oxygen we breathe, the water life depends on, the plate tectonics that drive geology, and the evolution of life itself. And what if our Sun had different properties, or we orbited two suns instead of one (and many stars are in such pairs)? Few books can bring so many topics together, and elucidate them all at once. And, in such an enjoyable read.

There are different types of speculation. The speculations in this book are based on our best understanding of astronomy, geology, and biology. Some of the scenarios in this book might better be termed as extrapolations, and in this sense they are on more solid ground than mere speculations. This is important to appreciate because this book will expand your understanding of our world. The author also tells you the parameters that go into the astronomical models, and even better, why other choices (say, for masses and distances) might be dead-ends for any interesting phenomena. If you enjoy astronomy, some of these scenarios actually exist in similar ways elsewhere in our solar system, so you'll understand more about many actual planets and moons.

The book has no equations and is very accessible. Educators, students, and the wider public will all find this book an excellent read.

The title does not fully convey the breadth and depth of the material this book covers. By asking a series of seemingly innocuous "what if" questions like "what if the Earth had two moons?" the author introduces the reader to the frontiers of cosmology, astronomy, planetary science, as well as basic physics that govern all the processes involved. You will learn about how the universe and all the elements in it were created and how those elements ended up in the Earth (and you for that matter), how spiral galaxies form and what happens when two of them collide, how Earth ended up with a solid crust covered by oceans and an oxygen rich atmosphere, and much much more.

Each chapter is preceded by a short, entertaining, pseudo-scifi type story describing events unfolding on an alternate "Earth" under each "what if" scenario, followed by a detailed scientific analysis of what would really happen. Particular attention is paid to whether each scenario would allow for sentient life to evolve on the alternate "Earth," highlighting how life on our Earth may not have evolved the way it has had certain conditions been even slightly different.

The book may not be an "easy read," as some reviewers have stated, especially if you are unfamiliar with various science concepts such as plate-tectonics, globular clusters, planetary nebulae, solar winds, etc.(A glossary of terms would have helped, but then, you can look up all these terms on the web.) However, you learn so much from reading this book that it is well worth the effort.

This book would be a great side reader for any astronomy or physics course. In fact, there is so much information in it that it can potentially be used as the textbook proper. All physics and astronomy students should read this book so that they get a feel of how the simple laws of physics conspire to create the vast and intricate universe around us, and how lucky we are to exist at the right time and place to be able to see and appreciate it. All science fiction fans should also read this book if they are to properly speculate about the possibility of extraterrestrial life.

Neil F. Comins is a professor of physics and astronomy at the University of Maine and has written a number of popular books including: The Hazards of Space Travel: A Tourist's Guide and What if the Moon Didn't Exist? Voyages to Earths That Might Have Been. In his new book, What if the Earth Had Two Moons, he gives us nine alternative realities, including what our world would be like if we had two moons. At the beginning of each hypothesis, Comins has a little fun with a short fictional reality existing in the condition he is about to describe, then he analyzes it from a scientific and then sociological perspective. While he tends to keep everything dry and scientific, and there seems to be a lacking in exploring the alternate world (perhaps that is a different book), Comins nevertheless is thorough and detailed, taking on what ifs like: "What if the Earth's Crust Were Thicker," "What if the Sun Were Less Massive," "What if the Earth had Two Suns," as well as many others.

Originally written on May 18 2010 ©Alex C. Telander.

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The author, while obviously knowledgeable and intelligent, is not a fiction writer and so fails as he tries to dress up his scenarios. He would have been better off just cutting to the chase and not presaging each chapter with an attempt at narrative fiction. Worse, is that if you can get through these laborious introductions, he tries to snazz up his 'what ifs' with fancy names for alternate 'heavenly' bodies. Perhaps it is just me, but I got thoroughly lost trying to keep track of all his weird and wonderful names. Both these things unnecessarily detracted from, an otherwise, very illuminating read.

This is a second book of this type for the author. In this book, he imagines additional scenarios in which an earth-like planet or Earth finds itself with some different variable. Each chapter changes the situation somewhat. In one chapter he imagines Earth with two moons. In other chapters he discusses ideas such as Earth being a moon of a larger planet, Earth being in a different part of the galaxy, Earth having a smaller sun and so forth. each chapter follows a similar format. They begin with a fictional story of some characters on the imagined planet in some situation that involves the difference being looked at and then the chapters go on to discuss the scientific and practical ramifications of the difference if it were really to be the case. In a number of cases, he discusses some basic astronomy issues such as the life cycle of stars or the makeup of galaxies.

This is a very interesting book because it makes you think not only about intriguing possibilities for other Earth-like arrangements, but also the actual situation of Earth itself. In a way, this book is sort of an attention-grabbing way of teaching astronomy by using interesting fictional scenarios to teach real-world issues. The reader not only learns about Earth's past, which involved very different things like molten crust, shorter days and huge tides, but also about the kinds of places life might be able to develop elsewhere in the universe. Many of the chapters obviously involved a great deal of calculation and research to determine things like how long a day would be on such and such a planet or how high the tides would be. Obviously, much of the material is highly speculative. For example, who is to say how long it would take sentient life to evolve, if it ever would on a planet in a different environment? Additionally, the author intentionally sets up his fictional planets to be just right for life. With probably trillions of planets in the known universe, it's very possible that some of these scenarios actually exist somewhere, but the point of this book isn't so much to talk about actual situations as to teach about astronomical effects. In a way, the whole book is like a big serious of thought experiments.

Personally, I found the book to be something of a page turner. While there were some sections that got a bit bogged down in extended discussion of things like how long a day might last on such and such a planet, overall, there were enough interesting ideas to keep my attention. I have only one complaint about the book. Both the fictional stories and the chapters themselves ended somewhat abruptly. The little stories at the beginning of the chapters would end right at some crescendo leaving you to think the wrap-up would come, but it never did. It would have been nice if the author had eventually gotten around to making reference to his stories later in the chapter or wrapping up what happened, but he leaves us hanging. Also, a number of the chapters just sort of end when a bit more of a summary would have been nice. These two things detract slightly from the effectiveness of the book. I think the stories and the chapters themselves would have been a bit more memorable had there been more resolution and summary. Because of this, I give the book 4 stars. If you are interested in astronomy, space, the evolution of life on earth or the potential for life on other planets, you will most likely enjoy this book. It injects the curiosity of a science fiction piece into the reality of the universe we live in.

Neil F. Comins has always been a mixed bag. Having read many of the original articles in "Astronomy" magazine that he later expanded in "What If the Moon Didn't Exist?", the briefer articles are often better through their concision. At chapter-length, I find myself getting a "just the facts, please" attitude, and that's no good. Yet, WITMDE has been a favorite read of mine ever since it was released.

Perhaps my criticism is not entirely fair. As a book that's exactly about its title, it's a fine, fun, and easy read, one that will appeal especially to SF fans and world-builders. Some have criticized this book for being overly technical, an assertion I vehemently disagree with; this book is so clearly aimed at neophytes that those with even an informal knowledge of geology and astrophysics will probably be left hankering for more scientifically rigorous fare. Furthermore, better organization and abundant illustrations make this work an improvement on its predecessor, overall.

The book falls short of perfect, less for the few glaring typos than for what the author chose to write. For instance, the Dichron chapter feels unfairly truncated, while the Futura chapter contains a long digression on the mechanics of interstellar colonization that, if it belongs in the text at all, should have been in its own chapter. The vignettes at the beginning of each scenario, though well-meant, are distracting.

Stylistically, I'd give the book three and a half stars if I could, but four is more honest; for all its flaws, it's enjoyable enough to win most people (myself included) over. And, if you haven't read WITMDE, get to it; it's a companion piece in every sense of the word.

This book debunks most fantasists and SF writers' astronomical absurdities. It gives good solid foundation for devising a universe, solar system or planet for a fantasy or SF setting that will at least bear critical scrutiny. This is important in the modern era of 'world-creation' that is a prereqisite for believable fantasy/SF worlds. The author is scientific, and covers most scenarios with their likely outcome and effect on cultures, even life itself. Thus a world with two moons is one with major tidal problems, and the subsequent effect that would have on trading patterns - would coastal settlements be so desirable?
Recommended for all would be world designers.

This book is a follow up to the book Comins wrote back in 1995. His earlier book was called What if the Moon Didn't Exist? In that book, which I also read and enjoyed, he described ten different scenarios for an alternate Earth, starting with a description of our planet but without its signature Moon. In this new volume, Comins follows the same format - he presents ten scenarios for alternate earths, and then describes possible effects on the inhabitants of the alternate Earth.

The first chapter is titled: What if the Earth Had Two Moons? Dimaan, Lluna, and Kuu. Comins likes to give his alternate Earths each a unique name. In this chapter, Dimaan is our planet, and Lluna and Kuu are the two moons that orbit it. Comins goes into great detail to describe how it might be possible for a planet like ours to have two large moons - it takes a bit of rigging, but eventually everything lines up in a stable system (its not permanently stable, but the two orbiting moons would not collide until a distant future). What would be different for the inhabitants of Dimaan? The tides would certainly be different, as would eclipses and night skies (the amount of moonlight would be 4x greater than what we Earthlings experience.)

The second chapter is titled: What if the Earth were a Moon? Mynoa and Tyran. This was one of my favorite chapters. It describes an Earth just like ours, except it orbits around a Neptune size planet - the alternate Earth (called Mynoa) is itself a satellite. This has some dramatic effects on the planet. The major effect is that Mynoa becomes synchronously locked to the rotation of Tyran - Mynoa will always present the same the same face toward the large planet. Inhabitants on one side of the Mynoa will see the giant planet Tyran overhead (I liked Comins description of the amount of light falling upon the inhabitants, as Mynoa goes through frequent eclipses as it circles Tyran), while inhabitants of the far side would see gloriously dark night skies.

Chapter three is titled: What if the Moon orbited backwards? Anillo. The moon of Anillo is called Noom - it orbits Anillo in the direction opposite from the direction of its rotation. Unfortunately, this has bad results. On Earth, the tides and the moon have the net effect of slowing the rotation of our planet, but also transferring the Moon in slightly greater orbit (our moon drifts further away by one and a half inches every year). But on Anillo, Noom will come closer and closer each year until a final catastrophic breakup when Anillo's gravity rips it apart. If one falling rock could wipe out the dinosaurs, imagine the prospects for any lifeforms on Anillo when an entire Noom disintegrates overhead.

Chapter four is titled: What if Earth's Crust Were Thicker? Dichron. This is another fascinating chapter, describing how different the planet would be if the crust were much thicker. This would interrupt the plate tectonics. Unlike our planet, where the continents move about, on Dichron everything will be fixed in place. But the heat from the of Dichron core is trapped in place. On Earth, there are 15 to 20 active volcanoes a year, which is how our planet radiates heat from the core. On Dichron, this heat will be trapped by the thicker crust, so it will keep building up until a "hot spot" develops and an entire section of the crust will liquify and melt through! There wouldn't be any permanent landmasses, after millions of years, every part of the crust would be melted and reformed. This would have some hazardous effects on any beings living on Dichron!

The remaining chapters are:

Chapter 5: What if the Earth formed Fifteen Billion Years from Now?

Chapter 6: What if There Were a Counter Earth, a Planet in Earth's Orbit on the Other Side of the Sun?

Chapter 7: What if the Earth had Formed Elsewhere in the Galaxy?

Chapter 8: What if the Sun Were Less Massive?

Chapter 9: What if the Earth Had Two Suns?

Chapter 10: What if Another Galaxy Collided With The Milky Way? This last chapter is a bit of a cheat, because the Andromeda Galaxy is already on a collision course with the Milky Way - our distant descendants will live through this collision.

I like this book because it is fun to think of alternate lifeforms and societies that might arise under these alternate Earth environments. Maybe a SF author will be inspired by these ideas and construct an elaborate alternate history. Or perhaps a director will create a film for a planet like Mynoa, orbiting around giant Tyran - that would create some memorable visuals!

But the counter-factual aspect of this book proved too much for me to resist. Ten Chapters pose What if questions. Each is prefaced by brief, illustrative vignettes, using whimsical names as stand-ins for the earth, the moon, the sun etc. The author, Neil Comins, tries to keep it real. In the chapter, What if the Earth were a Moon?, certain assumption have to be made. The Earth would be the same size as it is now. That is to hold a breathable atmosphere. Therefore, it would need a giant planet, (Neptune is used as an example) to hold it in place but close enough to the sun's habitable zone. This huge planet would be uninhabitable but early sentient beings on Earth wouldn't know that. Evolution would have taken a wildly different path. The relationship would be so much different. The sizes, the rotations, the tides, how the inhabitants adapt to day & night cycles vs. our current earth-moon relationship are foreign to us. That's what makes this book so entertaining. A spoiler here to let you know that in most of these scenarios the Earth come to grief eventually. But then we're doomed anyway.