Target Level: Middle School

Timetable: Two 40-minute class periods

Materials: Each student will need two copies of C3 "Wedges" image, one printed on card stock (To print image, click here); Colored pencils; Scissors

Vocabulary: Crosscutting relationships, crust, geologic unit, mid-ocean ridge, plate tectonics, relative age, seafloor spreading, subduction zone, terrain

Although the surface of Europa is frozen solid, there is the possibility that liquid water may exist underneath as lakes or even an ocean. Pictures taken by the Voyager and Galileo spacecraft show areas of the surface where large plates of ice have apparently broken apart and moved away from each other. Some have even twisted and rotated. The easiest way for these movements to occur is if the plates are floating on water, just like ice floes that fracture and shift in the polar seas on Earth. If the plates can be fit back together like a jigsaw puzzle, with their edges matching up neatly, it will provide strong evidence that the material beneath them was once liquid, or at least a warm, slushy ice. Let's try it and see!

Look at the image labeled C3 "Wedges." Differences in surface texture, color or shading show us that particular regions are made of distinct materials, formed in unique ways, or were created at different times. Making a geologic map is an easy way to show these differences. Using a copy of the C3 "Wedges" image, identify three areas of similar texture or shading. For now, avoid the smaller, narrower ridges. Lightly color each of the three surface types using a different color, even if they are not touching on the map (for example, color all smooth bright areas light green). When you are done, each color on your map will represent a unique geologic unit.

Now that you have made a geologic map of the area, can you figure out which unit is oldest and which is youngest? One way to determine relative age is to look for crosscutting relationships. Like a cake that is sliced, the surface rocks may be broken by a fracture or a fault. The unit (or slice) which cuts through the rock (or cake) is always younger than the rock itself. In other words, you can't cut something unless it's already there! Using the color as the name for each geologic unit, arrange them in order of their relative age in the space below.

Oldest-------------------------------------------------------------------------------------------------------Youngest

Now you will reconstruct the landscape to see how it looked at different times in the past. Using scissors, carefully cut up your map into the different geologic units you identified. Each piece should contain one color only. When you are done, place the pieces back together in their correct position in front of you.

Look again at the relative age of each geologic unit on the time line above. Carefully remove from your map those pieces that belong to the youngest unit. This will leave empty space behind. Can you fill the empty space by shifting together the remaining units? What kinds of motion did you have to use to do this? Do any features or ridges match up now that were once separated by the youngest unit? The surface you have created represents Europa at some time in the past.

Remove the pieces for the next youngest unit and shift the remaining pieces to fill the gaps. What types of motion were required this time? Do any features or ridges match up again? Compare this "original landscape" to an uncut C3 "Wedges" image.

As a final step, reverse the process and "rebuild" the surface of Europa one unit at a time. This should give you a clearer picture of some of the types of geologic materials, forces, and events that are responsible for shaping Europa's interesting surface.

1. List the types of motion you used to reconstruct the Wedges landscape.

2. What does this suggest to you regarding the physical properties of the material beneath this region?

3. Construct a simple graph showing the relationship between the brightness of each geologic unit and its relative age. What are some possible explanations for this relationship?

4. If a new geologic unit were to form in this region, would you predict it to be bright or dark?

5. Explain how the youngest geologic units you identified might have formed (i.e., where did the material come from?) Give the evidence for your answer.

6. a. If new ice or crust is being created in this region, and we find that the moon is not expanding or building mountains, what must be occurring elsewhere?

   b. Describe two ways in which this might occur.

7. Assuming that Europa's surface is no older than 100 million years old, as many scientists believe, calculate the minimum spreading rate for the dark wedge at left in the image. (Note: you will need to know that the image represents about 150 miles on each side)

Teacher notes are available here.

This activity was adapted from the following source by Brian Exton:

Tufts, B.R., Greenberg, R., Sullivan, R., and Pappalardo, R., 1997, Reconstruction of Europan terrain in the Galileo C3 "Wedges" image and its geological implications, Lunar and Planetary Science Conference XXVIII Houston, Lunar and Planetary Institute, p. 1455-1456.

Previous Section | Next Section

Top Level Europa Curriculum Module

Return to SSI Education Modules Page

Galileo K-12 Educational Activities Page

Return to SSI Education and Public Outreach Homepage

Galileo Solid State Imaging Team Leader: Dr. Michael J. S. Belton

The SSI Education and Public Outreach webpages were originally created and managed by Matthew Fishburn and Elizabeth Alvarez with significant assistance from Kelly Bender, Ross Beyer, Detrick Branston, Stephanie Lyons, Eileen Ryan, and Nalin Samarasinha.

Last updated: September 17, 1999, by Matthew Fishburn

Return to Project Galileo Homepage