When the Earth Had Two Moons

August 26, 2019
Asphaug, a University of Arizona professor of planetary science, takes readers on an initially promising, ultimately somewhat disappointing tour of the solar system. Exploring a variety of planetary forms—including comets, asteroids, moons, and the sun—he depicts the system in its entirety as a dynamic, complex, and deeply mysterious place. For instance, there’s Iapetus, one of Saturn’s eight moons, dubbed a “walnut moon” because of a 20-kilometer-high ridge that circles its equator, about which Asphaug concludes, “Ideas for how it formed are rather crazy, but one of them is true, or none of them are crazy enough.” Asphaug integrates his own research with that of others, yielding a firsthand account of cutting-edge science, including his titular hypothesis that early in Earth’s history it had two moons. He posits that the smaller satellite crashed into the moon, leading to the stark differences in composition between its two sides. He also hypothesizes about the origin of life, discussing how microscopic organisms might well have migrated among celestial objects. Asphaug makes for an enthusiastic and erudite guide to these and other subjects, but his overly technical language will likely frustrate general readers attracted by his compelling material.

Narrator Adam Verner's friendly, leisurely cadence immediately invites listeners into Eric Asphaug's discussion of the origins of our solar system. The renowned planetary geologist examines planetary formation, revealing new insights on perceptions of creation. From Kepler's laws to giant impact theory, Asphaug's concise writing style makes the subject accessible. Some of the information is complex, and Verner takes his time walking listeners through the material. In doing so, he captures Asphaug's conversational tone as well as his passion for his subject. Verner's engaging narration makes this audiobook enjoyable no matter what level of scientific background the listener has. D.M.W. � AudioFile 2019, Portland, Maine

October 1, 2019

Asphaug's love of the cosmos and his desire to understand the way it works led him to a career as a professor of planetary science at the University of Arizona. In this work, his passion shows clearly in his writing. The introduction asks readers to imagine Earth with two moons, one large and one small. The author opines that Earth had two moons at one point in the distant past, and notes that the far side of the moon is dramatically different from the near side as first shown by the Soviet space probe Luna 3 in 1959. The far side has a much thicker crust and more impact craters, while the predominant features of the near side are the large dark regions known as maria (seas). This and that the moon is slightly oblong suggest that Earth had two moons that eventually collided to form the moon we have today, an event that tells a great deal about the solar system itself. The author further explores how planets were formed, and why many are so different from one another. VERDICT A fun read from an award-winning scientist. Asphaug's literary skill shines throughout this entertaining work.--Dave Pugl, Ela Area P.L., Lake Zurich, IL

Copyright 2019 Library Journal, LLC Used with permission.

September 1, 2019
The sun and every body in its vicinity formed from the same primordial dust, yet every planet, moon, comet, and asteroid is different. This accomplished overview of planetary science describes the details. The first photograph from another planet was the rocky surface of Venus, transmitted from a Russian lander in 1975. More Soviet Venus probes followed, and while NASA has been responsible for most of the rest, other nations are getting into the act. The result, featuring contributions from high-tech telescopes and computer simulations, is an explosion of information about our solar system and, more recently, solar systems throughout our galaxy. An enthusiast as well as a fine writer, Asphaug (Planetary Science/Univ. of Arizona) lays it out from the beginning. Despite their flawed theories, when the ancients observed and calculated, they proved that Earth was a sphere and measured its diameter and the distance to the moon and predicted eclipses. Geniuses from Copernicus to Einstein improved the big picture, but it was well into the 20th century before interesting details became clear. That meteor strikes formed the moon's craters remained controversial until the Apollo landings proved it. After a nod to the Big Bang and formation of the sun, Asphaug concentrates on the history and current knowledge of the planets, familiar and unfamiliar moons, and unattached bodies in between. As an earthling, he favors earthlike features, and readers will share his pleasure as he discusses them. Rivers, lakes, oceans, and rain? Saturn's moon, Titan, has them; Mars and perhaps Venus once enjoyed the same. Life began in water, so scientists are thrilled when they find it elsewhere. Ice doesn't qualify, but there is evidence for liquid water oceans under the icy surface of Jupiter's Ganymede and Europa, Saturn's Enceladus, perhaps Mars, and even some asteroids and comets. An expert, entertaining review of what's known about the solar system.

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October 15, 2019
Asphaug, a planetary geologist and professor of planetary science at the University of Arizona, takes readers on a tour of the solar system and explains how planets are formed. He refers to the likes of Galileo and Robert Hooke as he writes about the history of the exploration of the moon via telescope. While exploring the formation of planets, he addresses how planets' surfaces are created, along with how planets are resurfaced, including the (literal) impact of craters and more. The author injects his own thoughts and research into his writing, including his work studying how a big splat may have created the mountainous regions on the far side of the moon. Black-and-white photographs from moon landings and planetary expeditions nicely complement the text. Extensive footnotes, endnotes, a glossary, and an index (not seen) are provided. Aspaugh's enthusiasm and expertise are apparent in his writing. Readers with some knowledge of planetary science will enjoy this book more than those looking for an introduction to the topic.(Reprinted with permission of Booklist, copyright 2019, American Library Association.)