Erik Asphaug’s When the Earth Had Two Moons (REVIEW)

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When it comes to writing books about space, few may be as qualified as Erik Asphaug. Asphaug has established himself as both an academic through his work as Professor of Planetary Science at various universities, and an impact specialist for NASA’s Galileo and LCROSS missions in 2006. His latest release, When The Earth Had Two Moons: Cannibal Planets, Icy Giants, Dirty Comets, Dreadful Orbits, and the Origins of the Night Sky, compiles the results of Asphaug’s research into a handy guide detailing space’s quirkiest phenomena.

Asphaug opts for concise explanations and astrophotography over the relatively abstract astrophysics and heady diagrams often found in top-selling astronomy books (Hawking, anyone?). Two Moons consistently keeps the casual reader in mind when navigating some of astronomy’s most pressing concerns. Neither wordy nor lacking, Asphaug successfully tackles everything from the intermediary state between stars and planets to NASA’s endless pursuit for liquid water in a mere 290 pages. He also addresses some of the most controversial topics in popular science: why was Pluto demoted to a “dwarf planet” (Blame the IAU and Neptune)? What would it be like to fall into Jupiter? (In Asphaug’s own words, it would be “a quiet but spectacular ride going in . . . the last part of the story is short: you’d punch through the cloud deck in a final hurrah. . . and ultimately crushed.”).

Two Moons aspires for more than just Jeopardy trivia. Rather, Asphaug’s insights showcase the paradigm shifts that have resulted from our millennia-old quest to understand the cosmos. He takes on the roles of philosopher, physicist, and historian in his attempt to reconcile the seemingly disparate approaches that mark astronomy’s history. Whether it’s the Ancient Greek’s commonplace acceptance of a round Earth by 350 B.C. or Ancient China’s discovery that the Moon reflects light rather than produces its own, Asphaug points out the astounding ingenuity of our ancestors that often goes unacknowledged.

Of course, Asphaug is a geologist at heart. As such, Two Moons devotes entire chapters to extraterrestrial topography, plate tectonics, and our seemingly endless pursuit for liquid water. In one of many sections devoted to the possibility of liquid water on Galilean satellites, Asphaug offers the following advice that sums up much of his career: “One mantra for planetary exploration is to follow the water.” While the media has often touted exoplanets as humanity’s next frontier, Two Moons
argues that the Solar System’s “geological weirdness” warrants further investigation. Although he admits that “it will be more challenging to send a robot down into the strange seas of [Jupiter’s moon,] Ganymede than to send a mission to the nearest star system”, Asphaug asserts that the elusive, yet undeniable presence of liquid water in our Solar System brings with it invaluable insights into the development of life on Earth.

Asphaug opts for concise explanations and astrophotography over the relatively abstract astrophysics and heady diagrams often found in top-selling astronomy books (Hawking, anyone?).

We currently stand on the edge of a new era in space exploration, in which the likes of Elon Musk and Richard Branson attempt to outcompete government-funded agencies. With it has come both a surging interest in monetizing space tourism and bizarre feats of flexing (such as launching a convertible into Earth’s orbit). Amazon CEOs and tech entrepreneurs may hog the daily headlines, but their escapades seem shallow and nearsighted next to the possibilities Asphaug offers in Two Moons.

While When the Earth Had Two Moons is stuffed with surveys and descriptions of clashing planets and otherworldly satellites, it also highlights the shortcomings found much closer to home. In describing encounters with Ph.d candidates who have never looked through a telescope and the Church’s retaliation against the Scientific Revolution, Asphaug implies that we stand as the biggest threat to space exploration: “If exploration is the yang of science, understanding is the yin. One cannot advance without the other.”

For more information, follow Erik Asphaug @smallplanets

WORDS: Aaron Tremper

IMAGE CREDIT: Custom House /HarperCollins

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