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What If the Earth Had Two Moons?: And Nine Other Thought-Provoking Speculations on the Solar System Hardcover – March 30, 2010

4.3 out of 5 stars 21 customer reviews

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Editorial Reviews

From Publishers Weekly

Armchair astronomers and hard SF fans who love a good game of cosmological What If? will find this an entertaining follow-up to physicist Comins's WhatIf the Moon Didn't Exist? Here he presents 10 more intellectual puzzles that explore new worlds, and imagine what life there might be like. Each chapter opens with a vivid glimpse of a hypothetical new world, such as in the title scenario, where Earth's gravity captures a second moon—a scenario that ends in destruction. Equally disastrous would be an Earth with a thicker crust—unable to form new volcanoes, hot magma would simply burn through the crust's surface, melting continents and the ocean floor. In another scenario, our solar system forms 15 billion years later than it did, prompting Comins to conjecture that aliens would have more time to traverse great distances to the planet and colonize it. This is a lucid, thoroughly accessible presentation of what might have been that is sure to make this volume as popular as its predecessor. 25 b&w line drawings. (Apr.)
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From Booklist

Stretching his scientific imagination, Comins tweaks the astronomical dials that control evolution on Earth, such as the length of the day, the height of the tides, or plate tectonics. He adds a second moon; he converts Earth into a moon of a Neptune-like planet; he reverses the direction of the Moon’s orbit; he puts an additional Earth into Earth’s orbit; he moves the solar system to other locations in the Milky Way; and in an ostentatious display of omnipotence, Comins makes Earth 15 billion years in the future. On these alternative Earths, of which Comins describes 10 in total, the evolutionary environment changes markedly once the author hits the start button. An astronomy professor and author of several successful science books (What If the Earth Had No Moon? 1993), Comins plays out his scenarios in physics-grounded narratives that all posit the same result despite different evolutionary paths: the rise of humans. Depicted in fictional predicaments that preface each chapter, they, warming up Comins’ factual explanations, create sf crossover appeal for this entertaining piece of popular science. --Gilbert Taylor
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Product Details

  • Hardcover: 304 pages
  • Publisher: St. Martin's Press; 1 edition (March 30, 2010)
  • Language: English
  • ISBN-10: 0312598920
  • ISBN-13: 978-0312598921
  • Product Dimensions: 6.4 x 1.2 x 9.6 inches
  • Shipping Weight: 15.2 ounces
  • Average Customer Review: 4.3 out of 5 stars  See all reviews (21 customer reviews)
  • Amazon Best Sellers Rank: #1,314,727 in Books (See Top 100 in Books)

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Top Customer Reviews

By Robert Busko VINE VOICE on April 22, 2010
Format: Hardcover
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.
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Format: Hardcover Verified Purchase
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)?
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Format: Hardcover
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.
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