SCIENCES

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

Custom House. Oct. 2019. 368p. illus. notes. index. ISBN 9780062657923. $28.99; ebk. ISBN 9780062657947. SCI
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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.

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