Martian Topography

Objective

Given high-resolution maps of Mars, students will explore the Martian surface and identify, measure, and describe the major geological landforms. These include large, individual objects (Olympus Mons and Valles Marineris), global features (the north-south dichotomy), and high-resolution surface images (erosion possibly due to flowing water).

Background and Theory

Mars, the fourth planet in our solar system, is similar to Earth in a number of ways. The coldest temperatures on the surface (-140 deg Celsius) are not far below polar temperatures here on Earth, and the high temperatures get up to a balmy 20 deg Celsius for short periods of time. Mars also has a thin but active atmosphere with clouds, weather systems, and winds that erode the surface. Both water and CO₂ ice collect at the poles, giving Mars polar caps much like Earth's polar regions (see picture above).

There are some striking differences. First, the thin atmosphere prevents water from existing on the surface as a liquid, so there are no large oceans (only ice at the poles). Second, since the surface has not been recycled by plate tectonics, it provides a record of Mars stretching back to the late heavy bombardment. Finally, dust and wind dominate the erosion on Mars, with some dust storms reaching global scales.

You will explore some of the unique geological features on the surface of Mars, starting with two famous, large objects and dominant global features, and ending with high-resolution images at a much smaller scale.

Procedure

Using the appropriate images linked in the sections below, answer the following questions. Record your answers on the worksheet provided.

Part A: Volcanoes and Valleys

1. Olympus Mons is the largest volcano in the entire solar system (at 24 km in height, it is about 3 times higher than Mt. Everest, at 8 km). It is surmounted by a complex summit caldera, and surrounded by a prominent scarp several kilometers high.
   1. Using this image, find the radius of Olympus Mons in km (the image scale factor is 1.8 km/pixel).

      Your value will be approximate; measure from the center of the complex crater to the "prominent scarp" or cliff-like ledge that marks the edge. (Note: if you keep the "x" or "y" coordinate about the same for both clicks, you can avoid the use of the Pythagorean theorem to calculate the distance between your two iclick positions.i)

   2. Using the fact that Olympus Mons is 24 km high, what is the slope of the volcanois sides? (Remember: opposite/adjacent = tangent of the angle. The angle is thus the inverse tangent of opposite/adjacent. Make sure your calculator is working in "degrees" and not "radians.")

      Need a scientific calculator?

   3. Compare this slope to our national highway standard of a maximum 6% slope. Comment on your comparison by relating what it is like to drive up or down a 6% grade (slope), where you see truck run-outs, for example, or the absolutely steepest highway you've ever driven up or down. The average grade to the top of Snoqualmie Pass is probably less than 1%!

2. Valles Marineris is a rift valley, perhaps formed when the Martian crust cooled. The entire valley is over 5000 km long (longer than the United States is wide).
   1. Using this image, measure the width of Valles Marineris in km (the image scale is 0.93 km/pixel). Use any criteria you wish, but state what you chose to define as ithe Valley."

      (Note: if you keep the "x" coordinate about the same for both clicks, you can again avoid the use of the Pythagorean theorem.)

   2. Because Mars is smaller than Earth and therefore has greater surface "curvature," if you were standing on one side of the valley, you would not be able to see the other side. (On a clear Martian day, you can see about 15 km away.) Recall pictures you have seen of the Grand Canyon. How does the view across Valles Marineris compare?

Part B: The north-south dichotomy

1. Visit the Google Mars Map. As soon as the first detailed images of Mars came back to the Earth, planetary scientists noticed the terrain in the north differed dramatically from the terrain in the south. Take some time to get used to how this webpage works. Look at some of the labelled items found in the lists (iRegionsi, iSpacecrafti, etc.) at the top left of the screen.

   • Pick a region in the northern hemisphere of Mars. Zoom in to one level of zoom lower than the highest zoom level. Count the number of craters that you see. Pan your view east or west and count again. Repeat this process for five different regions in the northern hemisphere. Take an average of your results to obtain a value for the “average number of craters per view area” for the northern hemisphere. Try to select regions which are not at the extreme north or right along the equator.

   • Repeat this process for the southern hemisphere. Try to select regions which are not at the extreme south or right along the equator.

   • Comment on the relative values of your two averages.

   • What conclusions can you draw from your results? Write a short hypothesis that might explain any differences in crater counts. If your results are not what you expect, then be sure to comment on this as well.

The Global Surveyor Mars Orbiting Camera (MOC) returned images in which the smallest visible feature is about 2 meters in size (about the size of you!).

1. All of the images from MOC are available from Malin Space Science Systems. Take a moment to check out some of the images.

2. The polar regions of Mars are of great interest to scientists. The poles record, in layering of ice and dust, periods of climate change on the red planet. These layers are about 10 to 100 meters thick. During the history of Mars, the climate has changed several times such that different layers have different amounts of ice and dust, changing their appearance. Look at these images. Read all of the caption If each layer represents 100,000 years of accumulated ice and dust, approximately how much of Mars' climate history is recorded in these layers? Recall (or find out) how atmospheric scientists use cores drilled in Antarctica for their studies. What do these cores (sometimes kilometers in length), tell us about the history of the Earth? Here we have another example of how comparative planetology works. We may know more after the Phoenix Mission lands in a northern polar region in 2008 and does some (shallow) drilling.

3. We have discovered what appear to be evidence of recent flowing water on Mars. Take a look at this these images, read a few of their captions, and answer the following questions.
   1. Study the alcoves, channels and aprons identified in the images. Using MOC2-234 as a model, draw and label a schematic map of a gully.
   2. Pick another image. Draw a map of this image and identify the same features. Be sure to indicate which image you chose.
   3. Compare these images of Mars and Mt. St. Helens. Name one similarity and one difference you see between these images.
   4. What is the main problem with the "recent flowing water" hypothesis used to explain these features? (Hint: recall Mars's atmospheric pressure.)