Pluto is Falling From Status as Distant Planet

Introduction | Task | Process | Guidance | Conclusion | Questions

Introduction
USA Today, March 28, 2001
     Like any former third-grader, Catherine Beyhl knows that the solar system has nine planets, and she knows a phrase to help remember their order: "My Very Educated Mother Just Served Us Nine Pizzas."
     But she recently visited the American Museum of Natural History's glittering new astronomy hall at the Hayden Planetarium and found only eight scale models of the planets. No Pizza - no Pluto.
     "That's because the museum doesn't consider Pluto to be a planet," docent Marjorie Kagan explained to Beyhl and other senior citizens on a trip organized by the Westbury Public Library. "Poor Pluto has been downgraded, knocked down."
     "Excommunicated!" interjected Beyhl, who got her basic astronomy from the nuns at St. Sylvester's Grammar School in Brooklyn in the 1930s.
     And now here was Kagan, preaching heresy. "We think Pluto is probably a comet. It's very small, very icy, and it has a very eccentric orbit," she told the visitors. Some looked as if they'd just been told "A" isn't a vowel or September hath 31 days. "There is a lot of disagreement about this, even in the scientific community," Kagan added. "But we think within five years everyone will agree with us."
     "I don't think it's gonna be missed," muttered one member of the group.
     "If it's a comet," replied another, "where's the tail?"
     The Westbury seniors had stumbled into a debate that might rewrite schoolbooks, render a million classroom astronomical charts obsolete and change how generations yet to be born build model solar systems. Is Pluto really a planet? And if not, what is it? Last year, the museum opened its astronomy exhibit inside a giant glass cube that's about 10 stories high and contains the Hayden Planetarium. The display grouped eight of the planets into two "families" - the "terrestrials" (Mercury, Venus, Earth, Mars) and the "gas giants" (Jupiter, Saturn, Uranus, Neptune). The ninth, Pluto, was quietly consigned to the Kuiper Belt, "a disk of small, icy worlds" beyond Neptune.
     But in 1999, the leading international organization of astronomers rejected a move to list Pluto as both a planet and Kuiper Belt object. Those who call Pluto a planet note that it has an atmosphere and a moon, Charon. It also is larger than any object yet observed in the Kuiper Belt.
     Other major museums still consider Pluto a planet, and some astronomers were appalled by the revisionism in New York. David Levy, the noted comet-finder, said the demotion was "off base." Alan Stern of the Southwest Research Institute's space studies department called it "absurd."
     Many non-scientists also spoke up for the outerdog planet. Docents at the Museum of Natural History get many questions from children, some of whom asked, "Where's my friend Pluto?"
     So this month, the museum installed a plaque titled "Where's Pluto?" and programmed an electronic kiosk to make the case to confused visitors.
     It goes like this: Science is the classification of similar things. Pluto has little in common with the two nearest planets, Uranus and Neptune. They are made of gas (Pluto is ice and rock) and are much larger than Pluto (which is smaller than Earth's moon). Also, Pluto's elliptical orbit is tilted 17 degrees from those of the other planets. So what is Pluto? "A breed of comet that lives in the outer solar system, never venturing near the sun," the display reports. "If Pluto were close to the sun, it would grow a glowing tail of sun-blown ice vapor." Compared with the other planets, it's "peculiar," "weird," "an oddball."
     Pluto's very planethood, the museum argues, is a historical accident. When Pluto was discovered in 1930, astronomers mistakenly believed it was roughly the size of Earth and alone in space. Not until the 1990s were many other chunks of rock and ice seen orbiting beyond Neptune in what is now called the Kuiper Belt.
     There is even a historical precedent for demoting Pluto. About 200 years ago, the asteroid Ceres was briefly labeled a planet when it was discovered between Mars and Jupiter. But then astronomers realized there were many such bodies in that ring of space and reclassified Ceres an asteroid.
     Not content to question Pluto's identity, the museum's astronomers argue that there's no generally accepted definition of the word planet. If Pluto is one, says Michael Shara, curator of the museum's astrophysics department, then so is Earth's moon and hundreds of other hunks of debris floating around the sun. Having said that, he added, "I just don't think Pluto is a planet."
     Some visitors take his word for it.
     "It's a surprise," Annie Prince of Manhattan said with a gulp. "But if they say it's so, I can live with it."
     Others, perhaps out of a sense of loyalty to lonely Pluto, refuse to be swayed. "I'll believe it's a planet until I see proof otherwise," said Evelyn McConnell, a mother chaperoning a class trip from Northport, N.Y. "It's nice to have all nine of 'em." But Neil de Grasse Tyson, director of the Hayden Planetarium, has been quoted as saying: "There is no scientific insight to be gained by counting planets. Eight or nine, the numbers don't matter."
     Which is not something Catherine Behyl would have dreamed of telling the nuns at St. Sylvester's.

The Task
Since 1997, NASA has sponsored an annual Space Day in which schools everywhere can participate. Your school will be joining in the celebration this coming year by investigating space and technology for the entire day. Your class has been assigned to design a display about the planets in our solar system. Each student in your class needs to contribute some type of planetary information that can be described using mathematics. For this project you need to present your information in a brochure, on a poster, or on a Web page. Be sure you include the following information:

• the data about planets that you will use for your project;
• three graphs, tables, or calculations that present the data you are using in some way. You can use all graphs, all tables, all calculations, or a combination of the three methods;
• diagrams or pictures that will make your project visually appealing.

The Process
To successfully complete this project, you will need to complete the following items.

• Find data about the planets of the solar system. For help, try these Web sites.
  www.nasa.gov
  nssdc.gsfc.nasa.gov
  nssdc.gsfc.nasa.gov/planetary/planetfact.html
  
• Brainstorm with several other students. Make a list of ideas for projects. Visit this Web site to learn more about Space Day.
  www.spaceday.com
  
• Consider various types of graphs that you could use to display planetary data.
• See the exercises in Unit 3 to help you with ideas for your project.
• Investigate other information about the planets. Visit these Web sites for additional space information.
  www.infoplease.com and search for planets
  observe.arc.nasa.gov/nasa/education/reference/orbits/orbit_sim.html
  csep10.phys.utk.edu/astr161/lect/history/kepler.html
  home.cvc.org/science/kepler.htm
  btc.montana.edu/ceres
  www.space.com
  www.howstuffworks.com
  
• Be creative. Add some additional data, information, or even pictures to your brochure, poster, or Web page.

Guidance
Here are some additional questions and ideas you may want to consider for your project.

1. What missions to investigate the planets of our solar system have been completed or are in progress? What were the results of these missions?
2. How many moons do the various planets have? Have there been any space missions to these moons?
3. Have other solar systems been located? If so, how far are they located from Earth?
4. How do telescopes work? What is the history of telescopes?
5. How do the missions and research conducted by NASA benefit people on Earth?
6. Have any companies begun to develop plans for space travel for civilians? What are the advantages and disadvantages of such programs?
7. Investigate Kepler's Laws. Verify the third law for each of the nine planets.
8. What is a light-year?
9. What discoveries have been made by the Hubble Space Telescope?
10. What is the eccentricity of an orbit? How is it calculated? Find the eccentricity of the orbit of each planet.

Conclusion
Here are some ideas for concluding your project.

• Present your project to your class or at a family night.
• Present the information on a Web page. Have other students critique your project and help you to make improvements to your project.
• Write a one-page summary of what you have learned from completing this project.

Questions

Lesson 8–3
For her project, Priscilla finds these data about the planets on a Web site. The table shows the perihelion (closest point to the Sun), the aphelion (furthest point from the Sun), and the average surface temperature for the nine planets. Notice that all distances are given as 10⁶ miles.

1. Copy the table and rewrite all the distances in scientific notation.
2. For which planet is the difference between the aphelion and perihelion the greatest?
3. Draw a scatter plot for the perihelion distance and the average temperature. Let distance be on the horizontal axis and temperature on the vertical axis.
4. Describe the scatter plot.

Lesson 9–1
For his project, Tyler makes a table that would help students and teachers make a scale model of the solar system. To start, he decides to average the perihelion and aphelion distances for the model. The table shows the distances.

1. Fill in the average distance column. Write your answers as values in 10⁶ miles.
2. What is a common factor of all the distances in column four?
3. Suppose you round each value in column 4 to the nearest 10. What is the greatest common factor of each distance then?
4. How can factoring the values for the distances help Tyler to make a scale model of the solar system?