Academic journal article Science Scope

NASA's Dawn Mission: Helping Define Planets, Dwarf Planets, and Asteroids

Academic journal article Science Scope

NASA's Dawn Mission: Helping Define Planets, Dwarf Planets, and Asteroids

Article excerpt

The decision by the International Astronomical Union (IAU) in 2006 to redefine the term planet has caught the attention of the public and students from grade school to graduate school. The IAU's decision has not changed the makeup of the solar system; it has merely offered a different way of thinking about the bodies that make it up. Both scientists and educators have debated about the change with regard to Pluto, but not as much has been said about the change in designation of Ceres, also designated a dwarf planet and one of the two targets of NASA's Dawn mission launching this summer (see sidebar on page 56).

The publicity generated by the IAU in 2006 has created a teachable moment for students around the world to consider the definitions of planet, dwarf planet, and asteroid with the potential for a better understanding of our solar system and how discoveries necessitate a change in the language we use to talk about it. This activity will enhance students' understanding of these new definitions through the use of a research-based instructional strategy called direct vocabulary instruction. This middle school vocabulary activity was developed for NASA's Dawn mission by educators at Mid-continent Research for Education and Learning (McREL) and their colleagues on NASA's Dawn team.

Summary of the activity

A six-step approach to direct vocabulary instruction has been shown "to improve students' background knowledge and the comprehension of academic content" (Marzano 2004). The steps are as follows:

1. The teacher provides a description, explanation, or example of the new term.

2. Students restate the explanation of the new term in their own words.

3. Students create a nonlinguistic representation of the term.

4. Students engage in activities that expand their understanding of vocabulary terms.

5. Students discuss the terms with one another.

6. Teachers periodically involve students in vocabulary games.

The activity on page 55 demonstrates how these steps can be used to introduce the IAU's new definitions of planet, dwarf planet, and asteroid. The activity can be applied in the classroom at multiple levels of interest. At the surface, this activity can be used to review the current scientific debate over the question, What is a planet? The fact that not all scientists agree with the IAU's classification scheme highlights the problems with classification and effectively demonstrates how science works. New discoveries require fresh analysis of existing theories and their supporting nomenclature. At a deeper level, this activity uses recent scientific events to inform students of the difficulties and shortcomings of classification in science, a concept often taken for granted at this age and among the general public. We, as humans, often attempt to demonstrate our understanding of the world by reducing objects and observations to categories, such as planets, asteroids, comets, and moons. Sometimes historical classifications have to be changed in light of new discoveries.

The process of science is obvious in this discussion. What is often thought of as scientific fact is really the currently accepted position that is awaiting further evidence to support or refute its accuracy. An informed discussion of the classification of Pluto and Ceres as dwarf planets can follow once students have completed this activity and mastered the new vocabulary.


Kendall, J.S., and R.J. Marzano. 2000. Content knowledge: A compendium of standards and benchmarks for K-12 education. 4th ed. Aurora, CO: McREL.

Marzano, L., and N. Christensen. 1992. Literacy plus: Games for vocabulary and spelling. Columbus, OH: Zaner-Bloser.

Marzano, R.J. 2004. Building background knowledge for academic achievement. Alexandria, VA: Association for Supervision and Curriculum Development.

A new way of thinking about the old solar system

Vocabulary activity: Dwarf planets as a new way of thinking about an old solar system

Step 1: Provide a description, explanation, or example of the terms. …

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