Impact Craters and Water on Mars

Goals

During this lab, students will:

• learn about an exciting aspect of the geology of Mars-the possible presence of subsurface reservoirs of water-relevant to current and future exploration of the red planet,
• learn about rampart-style impact craters and analyze impact crater geometries to explore the relationship between two key parameters, impact crater diameter and depth, that turn impact craters into powerfully useful probes of the subsurface, and
• analyze depth to water beneath a portion of the Martian surface, a process which requires graph construction, utilization, and explanation of data point outliers that may reflect spatial/temporal variations in water depth beneath the surface.

Skills

• Basic data entry, manipulation and display within Excel.
• Measure distances on an image (and in an advanced mode depths from Mars topography data using online tools) and use these data in calculations.
• Fit power and exponential trend lines to data to derive an equation relating crater diameter to depth.

This lab was developed for an introductory geology course focused on planetary geology, but is suitable for use in any introductory geology course. It is designed for completion in a single (3 hour) lab period with a write-up as homework. The object is to help students become familiar with Excel (if necessary) and to demonstrate how student-accessible analysis of planetary data they collect can be used to acquire immediate insight into an interesting and important geological problem, insight which itself raises interesting questions for more advanced study!

The example provided here teaches the basic method employed in a simple way, but it can be expanded readily in a variety of fashions to create whatever research environment is desired... students working individually or in groups can identify other areas to study and compare, for instance, as a way to promote student ownership of the effort.

Download (Acrobat (PDF) 179kB Aug11 05) the handout that is provided for students along with access to the two Mars images:

Image 1 (TIF version ( 1.7MB Aug11 05))

Image 2 (TIF version ( 1.7MB Aug11 05))

Teachers Guide to the Approach

Students do not need any pre-assignment knowledge of impact cratering.

Most students will follow the 5-step process described in the teaching notes.

The most common problem encountered when working with students on this assignment is ... (more)

Research Project, Part 2

To carry the project further, students can be asked to use interactive Mars data maps to pull up MOLA topography data and create profiles of selected features.

• Using the information from the lab (location, name of Xanthe Terra, etc.) they can use the web site to collect a topographic profile across one or more of the larger impact craters they think looks fairly "fresh"—it should be a crater shown within the study area for the project, and they will need to include a figure of the region and the crater(s) they measure to document what they did to receive credit.
• They can then be asked to consider how the actual measured depth(s) compares to the calculated depth(s) they obtained using the depth-diameter relationship.
  • Are there any implications for possible geological complications we might need to consider if we pursue this type of analysis further?
  • For example, this is a great mechanism for getting students to integrate thinking about erosion and deposition of sediments (which will modify the actual depth of the crater), infilling by lava, variations in target material properties, etc.
  • Will a global equation in fact be useful for examining a specific region?
• As an addendum to this, students could select an alternate area and make their own depth/diameter measurements using the MOLA topography data, then compare the two regions' data to explore implications for water beneath the Martian surface.

I prefer to use written assessments for these sorts of assignments, and I have the students prepare short reports that lay out their data collection approach, their data and results, and their analysis including possible explanations of data outliers.

A few useful web resources for acquiring research project data:

• great general entryway into many Mars missions
• Mars Global Surveyor mission home page
• MOLA team home page (more info) , see Data link for highest resolution datasets (256 pixels/degree, roughly 500 m/pixel) available for download if time/resources permit
• medium-resolution online profiler tool for collecting MOLA data profiles
• Map-A-Planet to create customized images (of Mars and other planets) for analysis; this currently includes Viking imagery such as that provided for Xanthe Terra as well as medium-resolution MOLA grids
• source of NASA public release images (more info) for all planets, with accompanying captions