Mars Cratering Teaching Notes
This material is replicated on a number of sites as part of the SERC Pedagogic Service Project
Teachers guide to the approachThe following 5-point section of text describes the process most students will follow.
- Load each image into the image program of your choice and adjust the brightness and contrast so that you can see the impact craters and their ejecta clearly.
- Measure the rim-to-rim diameter (i.e., the diameter of the hole, not the ejecta) of as many impact craters as you can. Be sure to write down for each one whether you think the pattern of ejecta makes it a rampart crater or not. You might want to label each rampart crater with a prominent "R", and when you're done measuring, be sure to save your image again with all the letters in place—I have a hunch you'll want to incorporate this into your write up a bit later.
- Build an Excel spreadsheet that records your data -- one column for a crater's diameter, and a second which indicates if it is a rampart crater or not -- and then use the formula capabilities of Excel to calculate the expected depth of each crater. To do this you will have to use Excel's Help capabilities to teach yourselves how to deal with an exponent in the equation.
- Plot the crater depth (Y-axis) vs. diameter (X-axis) in Excel, and add a power law trendline. Be sure to display the equation and R-squared value too. When you are done, save your Excel spreadsheet.
- You now have rampart crater data for impact craters of a variety of sizes. If water is necessary to form a rampart crater, what can you say about how deep the water is/was beneath the surface of Xanthe Terra?
- To answer this question, I ask the students to write a brief (1-2 pages plus figures) but thorough report describing their analysis -- a complete answer will include a labeled image, their data table and graph from Excel, and a clear expression (in short essay form) of their scientific argument concerning the depth to the water. A good format for their essay is here.
- It is useful to help the students remember that this problem, like most in science, is not black and white... if some of their observations don't agree with their main argument and the bulk of their data, they shouldn't ignore them, they should try to offer a plausible explanation for why this occurs (e.g., spatial variability in depth to the water table, temporal variability since cratering occurs over a prolonged period of time, etc.).