<p>What Happened to Pluto?!! </p><p>Scale in the Solar System, New Discoveries, and the Nature of Science </p><p>Mary L. Urquhart, Ph.D. </p><p>Department of Science/Mathematics Education </p><p>Marc Hairston, Ph.D. </p><p>William B. Hanson Center for Space Sciences </p><p>From Nine to Eight? </p><p>On August 24th Pluto was reclassified by the International Astronomical Union (IAU) as a “dwarf planet”. </p><p>So what happens to “My Very Educated Mother Just Served Us Nine Pizzas”? </p><p>Official IAU Definition </p><p>A planet: </p><p>(a) is in orbit around the Sun, (b)has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, </p><p>and <br>(c) has cleared the neighborhood around its orbit. </p><p>A dwarf planet must satisfy only the first two criteria. </p><p>What is Science? </p><p>National Science Education Standards </p><p>(National Research Council, 1996) </p><p>“…science reflects its history and is an ongoing, </p><p>changing enterprise.” </p><p>Beyond Mnemonics </p><p>Science is “ not a collection of facts but an </p><p>ongoing process, with continual revisions and refinements of concepts necessary in order to arrive at the best current views of the Universe.” </p><p>- American Astronomical Society </p><p>A Bit of History </p><p>• How&nbsp;have planets been historically defined? </p><p>• Has&nbsp;a planet ever been demoted before? </p><p><strong>Planet </strong>(from Greek “<em>planetes” </em>meaning <em>wanderer</em>) </p><p>This was the first definition of “planet” </p><p><strong>planet Latin&nbsp;English Spanish&nbsp;Italian </strong></p><p>Sun Solis&nbsp;<em>Sunday </em>domingo domenica dimanche </p><p>Moon Lunae&nbsp;<em>Monday lunes &nbsp; lunedì lundi </em></p><p><strong>French </strong></p><p>Mars Martis&nbsp;Tuesday <em>martes martedì marti </em>Mercury Mercurii Wednesday&nbsp;<em>miércoles mercoledì mercredi </em></p><p>Jupiter Jovis&nbsp;Thursday <em>jueves </em>giovedì </p><p>Venus Veneris&nbsp;Friday <em>viernes venerdì &nbsp; vendredi </em></p><p>Saturn Saturni <em>Saturday </em>sábado sabato&nbsp;samedi </p><p><em>jeudi </em></p><p>Copernican Revolution <br>(16th Century) </p><p>“Planet” now means “any celestial body orbiting the Sun.” The <em>second </em>time we’ve defined the word “planet.” </p><p>Copernicus <br>Ptolemy </p><p>Find these images and learn more about&nbsp;the Universe models of Ptolemy and Copernicus&nbsp;at </p><p><a href="/goto?url=http://www.pbs.org/wnet/hawking/universes/html/univ_coper.html" target="_blank">http://www.pbs.org/wnet/hawking/universes/html/univ_coper.html </a></p><p>In 1801, 20 years after the discovery of Uranus, Ceres was discovered by Giuseppe Piazzi. </p><p>Cerese was demoted to asteroid after the discovery of many other objects in similar orbits. </p><p>“Planet” became&nbsp;defined as “any celestial body orbiting the Sun that is ‘big enough,’ in other words Mercury-sized or bigger.” The <strong>third </strong>time we’ve defined the word “planet.” <br>The hunt for Planet X (1903-1916) </p><p>Clyde Tombaugh&nbsp;1904 - 1997 </p><p>Problems with Pluto’s mass </p><p>(this is the only scary mathematical plot that we’ll use here, we promise!) </p><p>from <em>Dessler and Russell (1980) </em></p><p>Discovery of Charon in 1978 </p><p>Images courtesy of the U.S. Navel Observatory and NASA/HST/ESA </p><p>Pluto and Charon </p><p>Pluto and Charon as imaged by the Hubble Space Telescope in 1994 </p><p>Image Credit: Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA </p><p>The <br>Kuiper <br>Belt </p><p>Image from <a href="/goto?url=http://www.ap.stmarys.ca/~ishort/Images/SolSystem/" target="_blank">http://www.ap.stmarys.ca/~ishort/Images/SolSystem/ </a></p><p>1992 QB1 </p><p>The first Kuiper Belt Object (KBO) was discovered in 1992 <br>Diameter: 200 km </p><p>A 1992 discovery image of 1992 QB1 (indicated by the arrow) captured by Jewitt and Luu using the University of Hawaii's </p><p>2.2 m telescope on Mauna Kea, from <a href="/goto?url=http://science.nasa.gov/headlines/y2001/ast13sep_1.htm" target="_blank">http://science.nasa.gov/headlines/y2001/ast13sep_1.htm </a></p><p>More Kuiper Belt Objects (KBOs) </p><p>More than 1000 KBOs have now been found. </p><p>100,000 may be detectable from Earth. </p><p>1000 km </p><p>Image Credit: NASA JPL-Calech </p><p>Neptune’s Moon Triton: <br>A Captured KBO </p><p>Image credit: Paul M. Schenk, Lunar and Planetary Institute </p><p></p><ul style="display: flex;"><li style="flex:1">Is Pluto Just a KBO? </li><li style="flex:1">UB313: Bigger than Pluto! </li></ul><p></p><p>An NASA artist’s conception (left) and an actual Hubble Space Telescope image (right) of a 2400 km diameter Kuiper Belt Object orginally called UB313, discovered by Michael Brown. </p><p>Credit: NASA, ESA, and M. Brown (California Institute of Technology) </p><p>So, What is a Planet? </p><p>Dysnomia </p><p>Eris </p><p>Image Credit: NASA, ESA, and A. Feild (STScI) </p><p>Scale in the Solar System </p><p>We’ll use a scale model of the solar system using a 1:10 billion scale factor, and including 8 planets and the first 3 dwarf planets: </p><p>1. Ceres </p><p>2. Pluto </p><p>3. Eris </p><p>Size? </p><p>“... anything bigger than TEXAS is certainly not minor, not small, and not a dwarf, </p><p>Therefore, a planet must be any star-orbiting, nonfusing celestial body larger than the smallest sphere containing TEXAS.” </p><p>-Bob Johnson <br>Graduate Student <br>UT Dallas </p><p><a href="/goto?url=http://www.johnstonsarchive.net/astro/planettexas.htm" target="_blank">http://www.johnstonsarchive.net/astro/planettexas.htm </a></p><p></p><ul style="display: flex;"><li style="flex:1">Smaller than Many Moons </li><li style="flex:1">Ida and Dactyl </li></ul><p></p><p>10 km </p><p>Roundness Criteria </p><p>Should everything round be a planet? </p><p>Saturn’s moon, Mimas Diameter: 394 km </p>