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When the Earth Had Two Moons: Cannibal Planets, Icy Giants, Dirty Comets, Dreadful Orbits, and the Origins of the Night Sky Hardcover – October 29, 2019

by Erik Asphaug (Author)

4.4 129 ratings

Part of: Cannibal Planets, Icy Giants, Dirty Comets, Dreadful Orbits, and the Origins of the Night Sky (1 books)

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An astonishing exploration of planet formation and the origins of life by one of the world’s most innovative planetary geologists.

In 1959, the Soviet probe Luna 3 took the first photos of the far side of the moon. Even in their poor resolution, the images stunned scientists: the far side is an enormous mountainous expanse, not the vast lava-plains seen from Earth. Subsequent missions have confirmed this in much greater detail.

How could this be, and what might it tell us about our own place in the universe? As it turns out, quite a lot.

Fourteen billion years ago, the universe exploded into being, creating galaxies and stars. Planets formed out of the leftover dust and gas that coalesced into larger and larger bodies orbiting around each star. In a sort of heavenly survival of the fittest, planetary bodies smashed into each other until solar systems emerged. Curiously, instead of being relatively similar in terms of composition, the planets in our solar system, and the comets, asteroids, satellites and rings, are bewitchingly distinct. So, too, the halves of our moon.

In When the Earth Had Two Moons, esteemed planetary geologist Erik Asphaug takes us on an exhilarating tour through the farthest reaches of time and our galaxy to find out why. Beautifully written and provocatively argued, When the Earth Had Two Moons is not only a mind-blowing astronomical tour but a profound inquiry into the nature of life here―and billions of miles from home.

Editorial Reviews

Review

“Delightful. ... The story swings from the birth of the universe, through the history of astronomy, to the modern understanding of the piece-by-piece building of the planets. ... Makes the solar system an even weirder and more wonderful place than it seemed before.” — Wall Street Journal

“A gripping and endlessly fascinating account of how planets formed.” — Alan Stern, planetary scientist and leader of NASA’s New Horizons mission to Pluto

"If the planets were born out of material orbiting the Sun, like raindrops condensing from a cloud, why do they differ so much in structure and chemical composition? This detailed book assesses the astronomical and geological evidence on the origin of planetary diversity." — Nature. "Best Science Picks of the week"

“When the Earth Had Two Moons is a lyrical exploration of our solar system, introducing not just the facts of its formation and nature but the implications for all of us living on Earth.” — Amy Mainzer, visiting scientist at the Jet Propulsion Laboratory and professor of planetary science at the University of Arizona

“An enthusiast as well as a fine writer, Asphaug lays it out from the beginning. . . . An expert, entertaining review of what’s known about the solar system.” — Kirkus Reviews

“Asphaug draws upon his years of research and expertise to provide the reader with a truly wondrous and surprising exploration of planet formation and the origins of life. A meticulous and expertly presented work of science, When the Earth Had Two Moons is unreservedly and enthusiastically recommended.”
— Midwest Book Review

“An enthusiastic and erudite guide.” — Publishers Weekly

About the Author

Erik Asphaug is a professor in the Lunar and Planetary Laboratory at the University of Arizona. He studies planet formation and evolution and has been on the science teams of numerous past and upcoming NASA and international space missions. He lives with his family in Arizona.

Product details

Publisher ‏ : ‎ Mariner Books; 1st edition (October 29, 2019)
Language ‏ : ‎ English
Hardcover ‏ : ‎ 368 pages
ISBN-10 ‏ : ‎ 0062657925
ISBN-13 ‏ : ‎ 978-0062657923
Item Weight ‏ : ‎ 1.27 pounds
Dimensions ‏ : ‎ 6 x 1.17 x 9 inches

Best Sellers Rank: #606,261 in Books (See Top 100 in Books)
- #36 in Comets, Meteors & Asteroids
- #333 in Geology (Books)
- #623 in Cosmology (Books)

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4.4 129 ratings

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Erik Asphaug

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Erik Asphaug was born in 1961 in Oslo, Norway, to parents who had immigrated to California after the war. He grew up in various parts of the US, and then back in Norway for his teenage years. He majored in English and Math at Rice University, and then taught high school in Minneapolis and Tucson. He tried his hand at graduate studies at the University of Arizona, and has been a planetary scientist ever since. In 1998 he won the Urey Prize of the Division of Planetary Sciences of the American Astronomical Society, and asteroid 7939 Asphaug recognizes his work on comet physics and impacts. He helped start the planetary sciences program at the University of California, Santa Cruz, where he became a full professor in 2006, and then was Ronald Greeley Chair of Planetary Sciences at Arizona State University from 2012 to 2017. He's worked on spacecraft mission projects from Galileo to MMX. Now he's a professor at the University of Arizona, back in Tucson, and lives with his family in the foothills of the Santa Ritas.

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Ralph Glasser MD

So deep it makes my head hurt…again!

Reviewed in the United States on January 20, 2023

Verified Purchase

So fascinating, after reading a library copy, I bought it to read again! Mind-bending theories on planetary creation, up to date concepts that shatter my generations-old understanding of the solar system. A must-read for astronomy lovers, meteorite enthusiasts, or anyone who just wonders from whence we came.
But, I read a paragraph at a time, put it down to ponder, “Ow, my head!”
Then read some more, or just sleep on it!

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Matthew Harris

scientific yet readable

Reviewed in the United States on February 13, 2020

Verified Purchase

having not read any other books about how our solar system formed, much of this information in the book I was encountering for the first time and didn't understand about 40% of it, but from what I could wrap my head around, I found it incredibly fun and engaging. It certainly ignites your imagination regarding the cosmos. Some nice features of the book 1) glossary of terms, very helpful 2) a list of planets and their moons with a specifications sheet that you can reference. 3) sprinkled illustrations throughout are only a secondary feature here and I think that's okay. I read another review that recommended reading the notes in the back. I agree, although it can get a bit arduous. It breaks the flow of the text somewhat and the writing is quite good so I found myself not wanting to break that flow. Flipping back and forth can get annoying, but the additional information and references listed enhances understanding. The author creates interesting analogies to help you understand phenomenon that can otherwise feel abstract. He has a clear passion and thirst for knowledge and understanding of the cosmos and he shares that excitement but also understands the limitations of what we can know simply due to distance between us and other stars and galaxies, but he has an admirable sense of hope that at some point we will begin probing further and further into the vastness of interstellar space. There are certain parts of this book that I will have to re-visit in order to better understand and to pursue some of the other sources and references listed. Exciting topic. exciting and readable book.

7 people found this helpful

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Huck Roberts

An enjoyable ride around our solar system

Reviewed in the United States on December 18, 2019

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If you are looking for a traditional astronomy textbook, look elsewhere. If you want a synthesis of modern physics (dark energy, black holes, etc) this isn't your book. But if you want an incredibly fun ride around our solar system (and what it may tell us about other planets out in the cosmos), then I highly recommend this book.

Asphaug blends personal insights with modern data intensive astronomy to give us a snapshot into both the process and the resultant theories of current planetary research.

One caution: don't skip the footnotes! Some really fantastic (and humorous) material hidden in there!

11 people found this helpful

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Michael Buratovich

Splendid introduction to planetary science

Reviewed in the United States on August 27, 2020

Verified Purchase

This is a beautiful, clear, introduction to planetary geosciences and astronomy. Anyone with an interest in planetary sciences can benefit from this book. It is nicely written and avoids rambling. It has just enough anecdotes and people stories to spice it up. The book is also well organized and satisfies the curiosities of readers. Highly recommended.

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Just another reviewer

The author can turn a phrase but, as another reviewer notes, rambles and rambles

Reviewed in the United States on July 7, 2020

The science content of the book is good, but it is not very organized. The author can write sentences well and choose words well, but structuring a book in a common-sensical way clearly is not the author's forte. There are way, way too many footnotes, some of which belong in the text and many of which should not be present at all. Some of the non-hard-science data are laughable, such as the claim that the Iraq War's accumulated total cost was as high as $6 trillion--a third of one year's GDP for the United States. The highest claimed number I have seen is $2 trillion, but most estimates are closer to half that amount. And try telling a lower- or middle-income taxpayer that $10 billion for a robotic space mission isn't all that much. I think space exploration is important, but $10 billion surely sounds like a lot to me! So if you contemplate buying the book, recognize that you will have to put up with a lot of rambling, but the science content you can glean contains a lot of gems. You will have to work hard a mining them, though.

2 people found this helpful

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Richard T Wilson

A great book for those interested in planetary and satellite formation and interactions.

Reviewed in the United States on June 9, 2020

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The book explains quite clearly how a lot of the planets and their moons could have been formed with the expert opinions and research from leaders in their fields. Presented in a logical and entertaining way.

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Aran Joseph Canes

A Whirlwind Tour of the Solar System

Reviewed in the United States on October 31, 2019

Verified Purchase

When I was an undergraduate physics student in the mid-nineties I remember seeing a presentation on how a golden age of astronomy was about to begin with the amount of data amassed by satellites and robotic expeditions.

Erik Asphang displays some of the results of this golden age. Steering the reader from Pluto to the asteroid belt to his own theory of when Earth had two moons, it feels a little like one is being whirled around the solar system.

Admittedly, parts can be difficult to follow. There is so much to describe that the narrative is strained by the need for brevity with such copious material.

And the material shared is mostly a combination of speculation on the formation of the solar system with a lot of geoscience. Readers not interested in the chemical makeup of various celestial objects will find these parts of the text tedious.

But the overall sense of wonder that beyond humankind’s everyday world there are planets, asteroids and stars undergoing changes that are every bit as dramatic as human history is a view that should be more widespread.

Overall, I found this book worth reading even if I did feel a little jolted by the roller-coaster. We truly are in a golden age of astronomical discovery. Not essential reading but probably the best popular guide to contemporary theories about the formation of our solar system. Recommended to all interested in such matters.

40 people found this helpful

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Ken Kabb

An interesting look at the history of the universe.

Reviewed in the United States on February 20, 2020

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Well thought out and extensively documented imaginative look at the development of our planet and the universe we live in.

One person found this helpful

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