Op-ed: Is Pluto a planet?

by David A. Weintraub

For the last week, astronomers gathered in Prague have debated, among other topics, what the right answer is to the question ‘Is Pluto a planet?’ This debate has captured the attention of huge numbers of people, many of whom have passionate opinions on this question. And now, by the vote of a small majority from among the 424 professional astronomers who happen to be members of the International Astronomical Union (IAU) – I am not – and who also bothered to attend the first part of the final plenary session of the meeting – more than 2000 persons attended the IAU meeting but did not participate in the vote – a decision has been made. The answer: vagueness and confusion. This debate will continue.

The headlines read “Pluto Demoted” and “Solar System Loses a Planet.” But the reality is not that simple. The newly approved definition creates a category of “planets” that includes Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The newly approved language also creates a category of “dwarf planets” that includes Pluto, Ceres, 2003 UB 313, and many more to come. So is Pluto a planet? Yes. It is a dwarf planet. Is Earth a planet? Yes. A plain old planet. Is Pluto different from Earth? Yes. Is Earth different from Jupiter? Yes. All of them remain planets. But our solar system has many different kinds of planets, and Pluto is not the same kind of planet as is Jupiter.

What, then, does all this debate mean? The debate means that science, in this case astronomy, operates in the public arena and that the knowledge derived from the scientific enterprise belongs to all of us. Astronomers are hired guns who have the privilege of uncovering the secrets of the distant universe. In the last twenty years, astronomers have discovered a part of the solar system completely unknown to us before, other than in informed speculation: the Kuiper Belt. The Kuiper Belt exists out beyond Neptune and we now know that Pluto is one of thousands of objects in the Kuiper Belt. The same process of discovery led, after the discovery of Ceres in 1801, to the discovery of the asteroid belt, of which Ceres is the largest object. With this international debate, many people are now more informed about the universe in which we live than they were last month.

In addition, new discoveries lead to new ways of thinking. Pluto must be thought of as part of the Kuiper Belt. Pluto is also a large object whose shape is determined by gravity and which has a primary orbit around a star (the Sun). This public debate permits us to start thinking about the solar system and about educating our children differently, better I hope. Children don’t need to memorize the names of planets. They need to learn about the universe and how we and the Earth fit into the universe. With knowledge comes empowerment to ask important questions, such as: Are most planets like the Earth and Mars or like Jupiter and Saturn or like Ceres and Pluto? And if the answer is ‘the Earth is unusual’ or ‘the Earth is like all the rest,’ how do we act upon that knowledge?

Weintraub is associate professor of astronomy at Vanderbilt University.

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