A Note from the Author: On August 24, 2006, at the 26th General Assembly of the International Astronomical Union (IAU) in Prague, by a majority vote of only the 424 members present, the IAU (an organization of over 10,000 members) passed a resolution defining planet in such a way as to exclude Pluto and established a new class of objects in the solar system to be called "dwarf planets," which was deliberately designed to include Pluto.
With the discovery of Eris (2003 UB313)--an outer solar system object thought to be both slightly larger than Pluto and twice as far from the Sun--astronomers have again been thrown into an age-old debate about what is and what is not a planet. One of many sizeable hunks of rock and ice in the Kuiper Belt, Eris has resisted easy classification and inspired much controversy over the definition of planethood. But, Pluto itself has been subject to controversy since its discovery in 1930, and questions over its status linger. Is it a planet? What exactly is a planet?
Is Pluto a Planet? tells the story of how the meaning of the word "planet" has changed from antiquity to the present day, as new objects in our solar system have been discovered. In lively, thoroughly accessible prose, David Weintraub provides the historical, philosophical, and astronomical background that allows us to decide for ourselves whether Pluto is indeed a planet.
The number of possible planets has ranged widely over the centuries, from five to seventeen. This book makes sense of it all--from the ancient Greeks' observation that some stars wander while others don't; to Copernicus, who made Earth a planet but rejected the Sun and the Moon; to the discoveries of comets, Uranus, Ceres, the asteroid belt, Neptune, Pluto, centaurs, the Kuiper Belt and Eris, and extrasolar planets.
Weaving the history of our thinking about planets and cosmology into a single, remarkable story, Is Pluto a Planet? is for all those who seek a fuller understanding of the science surrounding both Pluto and the provocative recent discoveries in our outer solar system.
Earlier this year, when astronomers officially "demoted" Pluto from its status as the ninth planet in our solar system, they little expected the public rancor that followed the decision. Vanderbilt astronomer Weintraub places the Pluto controversy in context in his judicious, lively account of the development of our solar system and the evolution of the meaning of the word planet, from Aristotle's theories to recent decrees by the International Astronomical Union. Assuming a geocentric universe, Aristotle argued that Mercury, Venus, the Moon, the Sun, Mars, Jupiter and Saturn were the only seven planets in the celestial realms. Later scientists notably Kepler, Copernicus and Galileo revolutionized astronomy by demonstrating that Earth and the other planets revolved elliptically rather than in perfect circular movements around the sun. By the mid-18th century, astronomers discovered other celestial bodies comets, asteroids and moons that often acted like planets by orbiting the sun and threw the definition of a planet into even more confusion. Weintraub effectively shows that Pluto is a planet by most definitions, but so are several other objects in the Kuiper asteroid belt. Weintraub's provocative, engaging study points to the richness and complexity of our solar system and its many possible planets.