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

by Neil F. Comins

“What if?” questions stimulate people to think in new ways, to refresh old ideas, and to make new discoveries. In What If the Earth Had Two Moons, Neil Comins leads us on a fascinating ten-world journey as we explore what our planet would be like under alternative astronomical conditions. In each case, the Earth would be different, often in surprising ways.

The title chapter, for example, gives us a second moon orbiting closer to Earth than the one we have now. The night sky is a lot brighter, but that won't last forever. Eventually the moons collide, with one extra-massive moon emerging after a period during which Earth sports a Saturn-like ring.

This and nine and other speculative essays provide us with insights into the Earth as it exists today, while shedding new light on the burgeoning search for life on planets orbiting other stars.

Appealing to adult and young adult readers alike, this book follows on the author's previous bestseller, What If the Moon Didn't Exist?, with completely new scenarios backed by the latest astronomical research.

Genres: Science, Nonfiction, Astronomy, Space, Adult, Alternate History, Research

304 pages, Hardcover

First published January 1, 2010

Reviews

[Terence · Rating 2 out of 5]

First the "good stuff":

The ideas alone get a minimum three+ stars in my reckoning. I've always liked SF stories that took me to truly weird worlds like Mesklin (Mission of Gravity) or Helliconia (Helliconia: The Classic Epic Trilogy in One Volume) and how the environments shaped the natives and the humans who (sometimes) colonized them. So in this book we get 10 scenarios about what an Earth-Moon system would be like if something were changed:

1. What if the Earth had two moons?
2. What if the Earth were a moon?
3. What if the Moon orbited backwards?
4. What if the Earth's crust were thicker?
5. What if the Earth formed 15 billion years from now?
6. What if there were a counter-Earth (ala Tarnsman of Gor, et al.)
7. What if the Earth had formed elsewhere in the galaxy?
8. What if the Sun were less massive?
9. What if the Earth had two suns?
10. What if another galaxy collided with ours? (This last scenario is going to happen in another 3 billion years or so, so if we have any descendants around at that time, they'll get to find out firsthand.)

Comins writes clearly, and even the most astronomically innocent reader should be able to grasp what's going on. The problem is the execution. Comins manages to make what should be some really exciting ideas sound...well...dull. Pedestrian. Ho-hum. And it doesn't help that he employs two extraordinarily annoying tactics. One, he introduces each chapter with a (mercifully) brief fictional episode set in the alternate Earth we're about to discuss. And, two, he feels he has to rename his Earths, as if you couldn't keep our Earth separate from his speculations. I skipped the fictions and gritted my teeth and tolerated the naming conventions.

I'd give this book a qualified recommendation to astronomy fans and SF authors looking to find exotic scenarios to put their heroes in but overall I was disappointed.

[Natalie aka Tannat · Rating 3 out of 5]

2.5 stars.

Parts of it were interesting, but nothing is really gained by reading the introductory vignettes. Unlike others, I won't criticize the renaming of the different scenario planets because of the way the names were subsequently used in the discussion. Thanks to the unknown library patron who pointed out the mistakes in the text which I had glossed over. Actually, some of the information was dated, even for 2010. Perhaps it's a consequence of the chapters having been written separately.

However, the almost exclusive use of Imperial units throughout is inexcusable. Talking about a scale of 10^-13 inches is nonsense. Talking about the temperature of stars in Fahrenheit is just...ugh (I don't care if he quotes them Kelvin too). The author even brought up slugs! [A slug is an American Imperial unit of mass.]

[Jennifer · Rating 4 out of 5]

This book, like Comins' earlier What If the Moon Didn't Exist?, contains a series of thought experiments about alternate Earths. This book is essential for science fiction writers and for anyone who's ever wondered what might have been. I especially liked the section 'what if the earth was a moon?' But each one of the book's ten chapters poses some interesting questions.

[Yael · Rating 3 out of 5]

Neil F. Comins, WHAT IF THE EARTH HAD TWO MOONS?

I am not happy with this book.

To be sure, the subject -- the question of what an earthlike world would be like if it had formed and evolved in different circumstances than ours, and what life would be like on such worlds -- is fascinating. Comins presents ten such scenarios:

1) What if the Earth had two moons?

2) What if the Earth were a moon?

3) What if our Moon orbited backwards?

4) What if the Earth's crust were thicker?

5) What if the Earth were to form fifteen billion years from now?

6) What if there were a counter-Earth, a planet in Earth's orbit on the other side of the Sun?

7) What if the Earth had formed elsewhere in the galaxy?

8) What if the Sun were less massive?

9) What if the Earth had two Suns?

10) What if another galaxy collided with the Milky Way?

This is the stuff of which the best science-fiction novels are made, the ones that explore the possible consequences of the natural laws that govern the universe as they impact a world and its life. This book should have been enthralling. And it was . . . up to the point at which dissatisfaction with its flaws got perilously close to outweighing delight at the scenarios Comin outlines here.

Some of those flaws were relatively trivial. For example, I have about the same reaction to stylistically and/or grammatically flawed writing that journalist Lynne Truss does, about like that of a master conductor or a musician such as Mozart or Bach to a long series of musical horrible discords. The standard fingernails-down-the-blackboard reflex anyone with decent hearing and an absence of Tin Ear Syndrome does. There are such problems in this book; I won't detail them, because they are relatively minor and really have no relationship to the things that are really wrong.

Which are:

Context: Neil Comins is a professor of astronomy and physics at the University of Maine, and the author of many popular books, articles, and textbooks on various aspects of science. He took his Bachelor of Science degree from Cornell, and a Ph.D. in astrophysics from University College, Cardiff, Wales.

And yet he presents us with statements such as the following:

"For stars with less than 0.4 times the mass of our Sun, the helium created by fusion bubbles out of the core and is replaced by hydrogen. This continues until the entire star is helium, after which fusion stops, and the helium star, called a red dwarf, cools off forever" [emphasis mine:]." Ibid., p. 214

I agree that up to the point at which fusion ceases in such a star, it fits the technical definition of "red dwarf," which is essentially a very low-mass star with no more than 40% of the mass of the Sun. But when its fusion candle finally goes out, from then on it is a white dwarf , a small star composed mostly of electron-degenerate matter. This slip of the light-pen may not seem serious, but Comins is, after all, an astronomer, and should be familiar enough with his subject not to make such a slip.

Another such slip, involving a cosmological principle, has to do with black holes. On page 188, he says:

"Contrary to common belief that black holes are giant vacuum cleaners in space that suck everything into them, weird effects only occur within a few radii of these objects. For example, if a black hole is a million miles in diameter, then bizarre behavior of space, time, matter, and energy occur only within ten million miles of the black hole . . ." [emphasis mine:]

In fact, a black hole is an object with infinite density and zero radius, which, according to the "No-Hair Theorem" of black hole physics, can be completely characterized by only three externally observable classical parameters: mass, electric charge, and angular momentum. (All other information -- for which "hair" is a metaphor -- about the matter which formed a black hole or is falling into it, "disappears" behind the black-hole event horizon and is therefore permanently inaccessible to external observers. And that means that a black hole has zero radius. It is the event horizon around it that has an appreciable radius, i.e., one greater than zero, and it is that which is the measure of how far the "weird effects" of a black hole on spacetime extend from that object.

These aren't trivial complaints. Young readers and others with little or no grounding in the sciences or experience of hard science-fiction of the sort Larry Niven and his colleagues write, which do pay close and reverent attention to state-of-the-art knowledge concerning physics, cosmology, chemistry, and astronomy, will, not knowing any better, almost certainly accept Comins' statements about such things gratis, and never think to question them except in the unlikely event they run across a book or article or science-fiction story or movie that prods their curiosity enough to make them review the matter and do some research of their own on it. And with our schools the sort of shambles they have become, especially when it comes to a real scientific education, that is tragic, for it is only through books like these that the lay public will ever have a chance to gain a real basic understanding of what scientists know about our universe today.

Thus I give this book three stars. It could have been worse -- but it also could have been so much better. {sigh}

[Christopher Desruisseau · Rating 4 out of 5]

Good what if book on astronomy and the effects changes would have on history.

[Rebecca · Rating 4 out of 5]

Absolutely fascinating thought experiments & completely packed with knowledge, not just limited to moons. I loved the short fiction that starts each chapter, it’s a great way to introduce each scenario & I wanted to know more immediately. I also thought the epilogue, a counter to the evangelists who (wrongly) jumped on the author’s first book, was poignant.

[Mark · Rating 3 out of 5]

What If Earth Had Two Moons
And Nine Other Thought Provoking Speculations on the Solar System
Author: Neil F. Comins
Publisher: St. Martin’s Press
Publishing Date: 2010
Pgs: 288
Dewey: 525 COM
Disposition: Irving Public Library - South Campus - Irving, TX
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REVIEW MAY CONTAIN SPOILERS

Summary:
“What if?” Science. The title questions and nine other scenarios about what Earth could be and what life, the past and the future would be like “If”.

Ten speculative essays with insights into Earth as she exists today and as she could exist tomorrow and the wheres, whys, and hows of other Earths that could exist and may exist out there around other stars.
_________________________________________________
Genre:
Science
Space
Astonomy
Astrophysics


Why this book:
Always fascinated by space and what ifs.
_________________________________________________
Favorite Concept:
This has a little bit of everything in it; how planetesimals react in a ring system, why galaxies further away seem younger, though they're not, the evolution of stars and spiral galaxies, etc etc. All kinds of lay astronomy and galactic cosmology.

So, Mizar and Alcor are both double stars. And Mizar, itself, is a pair of double stars. So, it is a six star system. One more star and that would be Isaac Asimov's Nightfall planet.

Hmm Moments:
Makes sense that the capture of the second moon almost destroys Dimaan, Earth in this context.

The idea of Earth as a moon of a gas giant was fascinating.

WTF Moments:
Horror of being Galileo was not what I expected to find in the opening pages of this book.

Meh / PFFT Moments:
Since all of these What-Ifs center on Earth, calling all of the planets in question by different names is a bit silly.

Wisdom:
Looking at all these scenarios and the potentialities, we’re probably really lucky that we only have one moon.

The question is easy to answer. The reason why we haven't had an interstellar visitor upset the solar system, the sun, or the planets, in the 4 and 1/2 billion years, is because space is big and there is a lot of empty space in it.

Juxtaposition:
In Nocturnal Hunter intelligent evolution, instead of an Arboreal Progenitor intelligence, on a two-moon planet, the dominant species would probably be feline or chiropteras instead of primates...or whatever the alien physiology version would be

So, the two moon system could become one after collisions and amalgamation leaving one large Moon. Possible. Equally, and I would say more likely, actually, space is big and empty. The two moons could miss each other for eons and epochs and possibly never, ever, collide. I submit that that's more likely.

The Unexpected:
Wasn't expecting the fictional accounts incorporated into this book.

So a moon orbiting retrograde is in a death spiral, interesting. Does that apply to all the retrograde moons orbiting the gas and ice giants in the outer solar system.

All these, various, what-if scenarios involving the Earth-Moon system are teaching me orbital mechanics without the math, excellent.

Missed Opportunity:
The Earth as the moon of a gas giant gives me a real Pitch Black feel. Doesn’t touch on what would happen to the planet and the life on it when the long term conjunctional eclipse happens as it no doubt would. Because, even if the moon-earth is tidally locked to always show the same face to the planet below, the gas giant would not suffer under the same limitation. Eventually, the moon-earth would fall into the long deep shadow and if that eclipse were longer than a day or two, things would get hairy for life on the surface of the moon-earth.
_________________________________________________
Last Page Sound:
Interesting questions, interesting answers. I'm glad the author used science to answer these thought experiments.
_________________________________________________

[Claudia · Rating 5 out of 5]

We all wonder about the enduring question 'What if?'
In this case, there are in 10 different speculations regarding the the Earth, planetary scientific variations and the background (as known in 2010) for each. In actuality, there are 16 as some possibilities can have multiple scenarios.

Once you're past the introduction which gives origin of this book - which this is actually the author's second book of what if's - you're asked what if the Earth had two moons. The author gives a little fictional excerpt of life on this alternative Earth and then the scientific explanation for this possibility.

And this is how every chapter flows. What if the Earth WAS a moon? What if the Earth orbited backwards? If the crust was thicker? If it formed 15 billion years from now? A counter-Earth which orbited in Earth's orbit but on the other side of the Sun - there are 3 different variations with this one. Two variants for if the Earth formed elsewhere in the galaxy as well as if our sun was less massive. Three variants if the Earth had two suns. And the one that is purported to happen billions of years in the future - if another galaxy collided with the Milky Way which Andromeda is forecast to happen.

Not being an astronomer, the science behind Comins speculation explanations seems completely sound and realistic without delving too deep in the complexity of stellar physics. We've all read and watched science fiction and even some fantasy which discusses alternative solar system arrangements but this book can give some of those arrangements a solid scientific base.

Personally, some of the views of life on these alternative worlds I wish could actually be expanded into a full-length fiction piece because they are interesting. Also, with the exploding discovery of exoplanets, these type of questions are becoming more relevant and intriguing.

[Lio Leeuwerink · Rating 5 out of 5]

In this book, Neil F. Comins explains 10 possible alternate origin stories for the Earth. In doing so Comins breaks down complex astrophysical and biological problems to layman's terms. Because of this, prior knowledge of the scientifical theories discussed in this book is unneccesary.

I thought the weakest points of the book are the little vignettes he uses to introduce each alternative Earth; most of them don't add anything to the book. Luckily they're not very long and can even be skipped if you really want to.

Read this book if you're interested in what life would be like if the earth had two moons, two suns, a smaller sun, was billions of years older, etc. Do not read this book if you aren't fascinated by space and science.

[Laura · Rating 5 out of 5]

I highly recommend this book!

I love how each chapter starts with a brief fiction story to give you a sense for how the changes to Earth would *feel*, and then the author transitions into hard science.

It turns out that in the process of explaining what effects various little changes (like adding a second moon) would have, you end up having to clearly explain how everything actually works right now, in the real world. I learned a lot more astronomy from this engaging format than I ever bothered to learn from a textbook. Bravo, Mr. Comins! It is a very well-done book.

(Side-effects may include questioning whether the beach-side economies of some of your favorite fantasy books that include two or more moons are actually practical...)

[Rachel McCollin · Rating 4 out of 5]

Mind boggling. I particularly enjoyed the little stories, a nice touch.

[Shaz · Rating 3 out of 5]

Two and a half stars

[Akash Meka · Rating 3 out of 5]

Intriguing for certain

[John · Rating 3 out of 5]

Lots of interesting situations posited and many interesting bits of cosmological, geological, and physical sciences thrown in. The theme which gets hammered again and again is if there are any "Earth like" planets out there, they're ultimately not going to be "Earth like" as we tend to think of a la 'Star Trek' or 'Star Wars'. In fact, even though every scenario posits life on these alternate Earths, you increasingly are given the feeling that life (or life sticking around for hundreds of millions of years or more) is shockingly rare.
I've read the book twice and still find myself struggling to deeply grasp the mechanics of how lunar tides are slowing the Earth's rotation while stealing energy which pushes the moon's orbit out further and further - but all the other scientific bits are clearly explained enough to hit home.
A bit like his earlier book, 'What If The Earth Had No Moon?', this one seems to lose steam a bit as it goes on. Some is by the nature of the repetitive effects ("Remember that thing we talked about in chapter 3? It's happening in Chapter 6's scenario, too.") - but it also feels a bit as if he's glossing over the later scenarios where it gets a bit too grim or unlikely, or perhaps it just didn't spark his interest as much.
Plenty of food for thought though, and a less threatening way to learn about the various scientific concepts snuck in, though. For science and science fiction fans alike.

[Dan Thompson · Rating 4 out of 5]

This is a collection of ten what-if scenarios for alternate earths in various solar systems. It includes the title scenario of Earth having two moons, how we would have gotten them, their effects on the Earth over time, and ultimately what’s going to happen to them. Other scenarios include the Earth as a moon, the Moon in a retrograde orbit, other planets in Earth’s orbit, Earth’s elsewhere in time, Earth’s elsewhere in the galaxy, and even what will happen to the Earth when the Milky Way and Andromeda galaxies eventually collide.

The nice thing about this for me is that he explores the science behind a variety of fantastical other Earths. In other words, he’s done much of the homework for exotic SF locales. Most of the science is well-written and aimed at the educated layman. A few bits got boring for me, but by and large it was good stuff.

However, this was not a particularly good Kindle edition. The text and diagrams themselves were decent, but the final 15% was taken up by a useless index (i.e. it had no links back into the text) and a collection of footnote/endnotes with no context back to the earlier text. Some of this may be simple limitations of the format, but I would have liked to have seen them handle it differently. If the index was going to be that useless, it should have been removed, and if there was no way to handle the footnotes more elegantly, they should have been inlined parenthetically in the text.

So, I enjoyed the book immensely, but I wish I had bought the dead-tree edition instead.

[David · Rating 2 out of 5]

It takes a bit of work to take such riveting questions and fascinating science and turn it into one of the most boring non-fiction reads I've experienced in a while, but Neil Comins manages to pull it off. My review won't add anything to previous reviews, but merely agree. The fictitious excerpts on these alternate worlds was a corny trick. Feeling the need to rename the alternate earths and other worlds (presumably to remind the reader that this really isn't how earth is) was just annoying. I don't think I'm being picky here. The device ruins any opportunity for the reader to feel any relation to the world that might have been, because so much care is given to make sure we don't think of it as our world. Coming off the latest book from physicist Michio Kaku, an author with an almost self-blinding passion for his material, Comins presents these bizarre alternate scenarios for our solar system in an emotionally detached style. And as another reviewer pointed out, he goes from talking down to the reader to throwing out some passages that probably require a prerequisite in a couple of collegiate astronomy courses to make any sense. Two stars is being kind, and entirely to the handful of interesting nuggets that escape the unriveting parts that surround it.

[Alex Telander · Rating 3 out of 5]

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.

For more book reviews and exclusive author interviews, go to BookBanter.

[Cal · Rating 3 out of 5]

I like the ideas and the guy clearly knows what he's talking about, but it was pretty boring, sadly. For me, he spent way too much time talking about how the planet would come to exist and not enough time exploring or explaining intricacies of what a "present day" would look like. I wasn't a fan of the fiction or renaming either, although I suspect I know what he did the renaming. The names themselves had me kinda eyerolling (Zweisonne? really? Well the inhabitants must be pretty dull if they don't realize they have two suns). As for the science, I've taken a college astronomy course so I know the basics, but his writing felt as once beyond my grasp and overly obvious. He endeavors to explain the basic concepts of astronomy, such as how stars work, which suggests he is aiming this book at the average Joe, but then he goes off in concepts that are much too complicated for the average uninitiated person to understand. I found my mind wandering every other paragraph.

I ended up through chapter 9 but then I had to return it to the library after having it out for 2 months.

I didn't get as much out of it as I would have liked.

[Gaabriel Becket · Rating 4 out of 5]

I love Neil Comins and recommend this to anyone willing to give it a crack. Reading these essays on how single, but pivotal, changes to our solar system or our planet or our moon would effect the earth and life on it, really sparks and invigorates the imagination. These are great fun to read and to think and imagine with and Comins takes the reader through the ripple effects single differences might make. Two moons, as opposed to one, is just one example: how would it effect gravity and water and the development of life on the earth and how different might things be? With this, I'd recommend "What if the Moon Didn't Exist," also by Comins, filled with more imaginative essays of speculative physics and evolution.

[Christine · Rating 5 out of 5]

I don't normally comment much on a book, but this one I loved. I'm normally a very fast reader, but this one did take me 25 days to get through only because I did get a little bogged down with the actual science/math he put into the book. And occasionally his suppositions took a little bit of thought too. However, it would be facinating to find "earths" like this and see how accurate everything he proposes is. I believe I saw that he had a book prior to this starting with the postulation of what the earth would be like with no moon. I may have to look into that one.

[Sally Lopez · Rating 4 out of 5]

Very enjoyable. I would have liked longer sci-fi sections that better introduced the explanatory parts, so I could have made more connections and been more fascinated by the differences each planet has from Earth. That would have made the book significantly longer, though, and maybe Comins wasn't ready to go deep in the story-telling realm. In all, highly recommended. I read Orson Scott Card used this book to plan the world in which his new Pathfinder series is set.

[Deanna Necula · Rating 2 out of 5]

I can read dense scientific books with pleasure, but this, despite its layman-friendly premise, is simply too boring. I almost couldn't make it past the introduction. I'm somewhat disappointed, because I have the distinct impression I'm missing out on some interesting nuggets to come, but I believe my time will be better spent with a more interesting, and better-written book. Don't even get me started on the odd and far-too-long fictional vignettes opening each chapter. Ugh.

[Blair Conrad · Rating 4 out of 5]

Interesting popular science book about how Earth-like planets might've developed under different astronomical circumstances. Not too deep, and each article is prefaced by (a pretty superfluous) story set on the planet to be discussed. Fairly fun, with the best bit being the one about Earth being a moon.

[James · Rating 5 out of 5]

Great science writing. As the title indicates, the author starts each of ten scenarios by imagining a solar system differing from our own in a different way - Earth with two Moons, Earth as a moon of a gas giant, etc.; then he explores the conditions that would result on Earth's surface and how - or whether - human civilization might form as a result. Good for adults or bright kids.

[Marc94 · Rating 2 out of 5]

This book was ok, but it got a little dry and at times the explanations could go from very elementary to more complex. However, I did like imagining what these various worlds would be like. If I could pick one to visit, I'd choose Mynoa the Earth-moon, orbiting the Neptune-like Tyran. Definitely not one of the better books I've read, it nevertheless threw out a few interesting concepts.

[Jo · Rating 4 out of 5]

A nice way to learn astronomy concepts through a series of thought experiments that could easily expand into works of science fiction (though some scenarios were more interesting than others, and the mini "stories" that begin each chapter were a bit cheesy). I particularly appreciated the way each scenario drew on the foundation of understanding from the previous ones.

[Jeff Brateman · Rating 4 out of 5]

Good intro read for those with or without an astrophysics background about the how and the effects of different situations having to do with the moon, earth, and sun placement. Pretty quick read, but I did skim a lot of it because it got repetitive.

[Lucy · Rating 3 out of 5]

It was interesting to read a book that by discussing different what-if scenarios involving the earth or the moon, ended up teaching me about so many different branches of science. Odd to see how much I've forgotten and how much I never learned...

[Dane Mamula · Rating 4 out of 5]

Book asks and answers some really weird questions..."what if", questions to be precise (as if you couldn't determine that from the title). But almost all of them are really well-thought out and based off fact, not just some rabbit out of the hat mysticism. Good stuff.

[Vic · Rating 3 out of 5]

Spent more time and went more in depth than what I was hoping to find. Still and interesting read and had I been in a different mindset I may have rated it higher. It is fascinating to know how much has to line up for life to exist the way it does on our planet.