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Teaching What a Planet Is: A Roundtable on the Educational Implications of the New Definition of a PlanetAbstractPrefaceTable of Contents and CommentatorsA. INTRODUCTIONB. THE SCIENTIFIC ISSUESC. THE EDUCATIONAL IMPLICATIONSAPPENDIX 1APPENDIX 2Reader ResponsesVolume 5Issue 2Teaching What a Planet Is: A Roundtable on theEducational Implications of the New Definition of a PlanetConducted by Andrew Fraknoi Foothill College and the Astronomical Society of the PacificThe Astronomy Education Review, Issue 2, Volume 5, 2006© 2006 Copyright assigned to the Association of Universities for Research in Astronomy, Inc.AbstractA quick review of the August 24, 2006, decision by the International Astronomical Union about how todefine a planet in our Solar System is followed by commentary from planetary scientists and educatorsfrom various settings. A table of relevant dates and a list of useful resources are appended, and readers areinvited to participate in the discussion. PrefaceReaders of the Astronomy Education Review are often the ones on the front lines of our educationalsystem, teaching students, meeting with planetarium and museum audiences, and responding to mediarequests for information. Given all the hoopla about the new definition of a planet in our Solar System bythe International Astronomical Union (IAU) at its meeting in Prague in August 2006, we thought it mightbe interesting to gather a cross-section of reactions from noted astronomy educators and then invite ourreaders to voice their opinions.We begin with a personal report by David Morrison, who was in Prague and served on one of thecommittees that considered the issue of defining a planet. This is followed by comments from OwenGingerich, the chair of the IAU Planet Definition Committee, and a statement from Richard French, thechair of the main organization of planetary astronomers in the United States. We then continue withcommentary from a number of planet experts and several formal and informal educators, including threetextbook authors. (The authors of each comment wrote independently, and there is thus a small amount ofoverlap in their comments that we have left in when needed for clarity.)At the end, we invite readers to join in the discussion. A table with the history of the number of planetsbeing taught and a resource guide of relevant readings and Web sites are included as appendixes. —Andrew FraknoiMy Very Educated Mother Just Said, "Uh-oh, No Pluto!""What’s in a name? that which we call a rose by any other name would smell as sweet."Shakespeare, Romeo and JulietTable of Contents and CommentatorsA. Introduction 1. David Morrison, NASA Ames Research Center 2. Owen Gingerich, Harvard-Smithsonian Center for Astrophysics B. The Scientific Issues 3. Richard French, Wellesley College 4. Steven Soter, American Museum of Natural History 5. Mark Sykes, Planetary Science Institute 6. Gibor Basri, University of California, Berkeley C. The Educational Implications 7. Debra Fischer, San Francisco State University 8. Eric Chaisson, Tufts University 9. Larry Lebofksy, University of Arizona 10. Jay Pasachoff, Williams College 11. Cary Sneider, Museum of Science, Boston 12. Dale Cruikshank, NASA Ames Research Center 13. William Hartmann, Planetary Science Institute 14. Paul Knappenberger, Adler Planetarium A. INTRODUCTION1. David MorrisonNASA Ames Research CenterAs a participant in the recent International Astronomical Union (IAU) meetings and votes on the definitionof a planet, as well as previous debates on the same subject, let me note some of my thoughts on both theprocess and the result.First, let’s look at the actual new IAU definition of a planet in our Solar System. Note that the upper limitin size for a planet (distinguishing it from a brown dwarf star) had earlier been set by requiring that it mustnot have sufficient mass to derive energy from fusion reactions at any point in its evolution. To this upperlimit we now add,The IAU . . . resolves that planets and other bodies in our Solar System be defined into three distinctcategories in the following way: (1) A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for itsself-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round)shape, and (c) has cleared the neighborhood around its orbit.(2) A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for itsself-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round)shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite [of a planet].(3) All other objects orbiting the Sun shall be referred to collectively as Small Solar System Bodies.The IAU further resolves that Pluto is a dwarf planet by the above definition and is recognized as theprototype of a new category of trans-Neptunian objects.This new definition is controversial, and not just among scientists. Such public interest is appropriate,because the definition is not primarily a science issue. No scientific study or mission has been waiting forthis decision, and scientists can (and often do) use all sorts of jargon without official approval. The wholeissue is of interest primarily because nonscientists, including school textbook writers, want a definition.Now they have one. It remains to be seen whether planetary scientists will adjust their terminologybecause of the IAU votes.The process was highly convoluted. I was a member of the IAU committee of 19 elected planetaryscientists who debated for months and finally adopted a definition by a vote of 11–8, in which Plutoremained a planet, along with any new objects discovered with a radius greater than 1000 km. This proposed definition, which would eventually have led to several new trans-Neptunian planets, wasnot even on the table at the IAU. Instead, several versions were debated that were formulated by acommittee (which I was not on) chaired by historian of science Owen Gingerich. Rightly or wrongly,many astronomers considered this process to be lacking in transparency, and they seemed to be unwillingto trust their representatives on either committee. During the IAU meeting, the Gingerich committeereported and alternate suggestions were made, so that the issue was in a constant state of flux. This processultimately led to a public vote on a series of issues, with no amendments allowed. The vote was taken


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