Solar System Search

In previous years, we have always specified the exact nature of the mission challenge at the very beginning of the unit. By its very nature, our video is about planning a mission to the planet Mars. However, we began to wonder if the students would be even more invested in the unit if it were they rather than the adults who decided that the class would plan a mission to Mars.

Our unit historically has used the 7-minute Mars Mission Challenge video as the initial event that preceeded the problem generation activities and the eventual curriculum. For the 1994-95 implementation, we allowed the students to "pick" which planet (or moon) they thought would be the best candidate for human exploration. In a sense, this was still somewhat predetermined since we believe that the planet Mars is the most practical place to visit in our solar system outside of our own Moon. There are alternatives, however. The Jupiter mood of Io has long been considered a possibilitity, along with one of the twin moons of Mars, Phobos and Deimos.

The activity began as a trip-planning problem. "If we wanted to visit someplace in the universe other than our own planet and our Moon, where would we go?" Interestingly enough, our nearest star, Alpha Centuri, came up first. The students rationalized that since it was a star, it had planets which could be explored. It was a reasonable deduction for the students to think that since our Sun - a star - had planets, then Alpha Centuri - a star - would have planets. However, with some quick referencing, it was determined that Alpha Centuri was 4.5 light years away. This provided a good introduction to the concept of a "light year" and it presented a way to have the students understand the enormous distances that separate us from other stars in our own galaxy. It was quickly determined that because of the distance and the impossibility of traveling at the speed of light at the current time that Alpha Centuri was not a practical consideration.

With some deliberation and group planning, the students began to look more closely at our own solar system. As we had expected, the students were narrowing their focus in the right direction. The consensus of the group changed from thinking that Alpha Centuri was the best choice, to realizing that our own solar system offered the best possibilities. At this point, the classroom teacher decided it would be best to form mini-groups that would look at the feasibility of a human expedition to each planet. Groups consisting of 2 - 3 students were formed and the students were given as much choice as possible in determining which planet or moons of a planet they wanted to research.

Another critical step to this pre-unit was in the determination of what aspects of the problem the class needed to answer. During a pivotal class session, the students, with the guidance of the teacher, generated a list of critical information that each group would have to present in order to answer the question. Groups could do more research if they wanted, but the class agreed that there was a minimum amount of information that each presentation should contain. The specific criteria developed by the students in whole-class discussion were:

- Size of the planet
- Time of orbit around the sun
- The force of gravity on the planet surface
- Overview of the climate
- Atmospheric conditions
- Seasonal temperature at the equators and poles
- Distance from the Earth
- Expected travel time to that planet from Earth

After 3 days of research, each group made a presentation concerning the feasibility of a human expedition. Some planets (specifically the outer planets) were ruled out due to the long distances and the fact that they were primarly gas giants (except for Pluto). The inner planets of Mercury and Venus were extrememly hostile, leaving only Mars as a viable candidate. The "Neptune" group argued convincingly to the class that their planet would be great to explore if a space station could be built above the planet and then send a crew to explore the surface using space-walk techniques. Other groups argued that this was beyond current technology and was thus ruled out. Nonetheless, the activity proved to be very beneficial at having the students develop a shared knowledge base as well as raising the discourse of the class to a higher level. The format was similiar to a debate format in which the students had to make a persuasive argument. Such formats can be extremely beneficial in raising the collective knowledge base of the class.

In this case, the students began to understand the factors that make Mars so attractive - a relatively moderate temperature, polar ice caps that may contain some frozen water, plenty of oxygen in the vast amounts of carbon dioxide on the planet. Mars is also a reasonable distance away, and the students did not think of a two- or three-year mission as being out of the question (especially after realizing the distances between planets in our solar system). These factors, combined with the elimination of other possibilities (Venus is too hot and hostile, Mercury is hot and desolate, Jupiter is a gas giant and very far away) resulted in other planets quickly becoming secondary choices once the comparative benefits of Mars were realized.

1. Writing and sharing their final reports
2. Drawing graphics depicting their own visualizations and conceptualizations
3. Setting up discussion notes on:

a) exploration in general
b) criteria needed for each group to answer
c) benefits (if any) of exploration

Starting off the Mission to Mars unit with this activity may also have some untested affective or motivational benefits. For example, we believe this activity stimulated interest and curiosity by allowing for real student choice in deciding what planet they believe to be the best to visit. This fits very well with current research on motivational aspects of learning environments. As the class explores their options for this task, they realize that a mission to Mars is really the only practical choice given present-day technology. While we could have told the students Mars would be the only practical decision Ñ imposing the choice on them Ñ this pre-unit activity placed the decision-making in their hands.

Scale Model

This benchmark lesson was devised in order to introduce the student to factors which were essential for a preliminary understanding of the relative scale and size of the solar system. From experience in the classroom, the teacher knew that issues of relative distance and size of the planets were not especially tangible to grade school students. In order to facilitate discussion of these relationships, he introduced the concept of an astronomical unit (A.U.) which is the distance between the Earth and the Sun. This unit of measurement was devised by scientists to facilitate discussion of planetary distances. Presenting the astronomical unit to the students served two purposes: 1) it introduced proportional reasoning, and 2) it introduced students to the real vocabulary of the scientist as they constructed a physical model of the solar system. The resulting manipulation and appreciation for scale was intended to raise the level of discourse in the classroom from "millions of miles from the sun" to "relative distances" from the sun.

Through the course of a benchmark lesson, class discussion centered around the utility of using an unconventional unit of measure. Attempts were made to have the students spontaneously generate the astronomical unit, (A.U.). While this was never fully realized in the class, through guided discussion the researcher was able to use comon analogies (feet, yards, miles) as a way for students to appreciate the practicality of using a unit of linear measure substantially larger than a mile when talking about the enormous scale of the solar system. Future lessons introduced the "light year" as a unit of measure when speaking about distances between objects in the universe.

A physical model is an actual device that is similar enough to the real-world article being modeled that we can hope to learn something from its construction and/or manipulation. Typically, although certainly not always, a physical model is easier to work with than the article it represents since it is either smaller, offers a unique perspective, or takes a shorter time to see a full cycle (i.e., a model of the earth spinning on its axis).

Many textbooks and teaching manuals offer suggestions for making scale models of the solar system. While this benchmark focused on linear distance, another lesson could eventually be envisioned in which the sizes of the planets and Sun were estimated. This would introduce the concept of scale as students begin to realize that as objects (planets) increase in size, their volume increases faster than their surface area. For our lesson, we utilized the following common items suggested by Gustafson (1992):