Astronomy 105G Lecture Notes, 12 Mar. 2004

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Mars' Polar Caps

Mars has permanent polar caps at both the North and South poles. They are composed of water ice and CO2 ice. One component of the polar caps is sesaonal, meaning it comes and goes depending on the season. The other component is permanent, and never completely vanishes. The permanent cap over the South Pole is made of CO2 ice, while the permanent cap over the North Pole is made of H2O ice and is much larger.






South Polar Cap as seen by Viking





At high resolution, the permanent caps are composed of many layers of terrain, probably due to the long-term history of deposition of frost and dust onto the surface. By studying these layers, planetary scientists can learn something about long-term climate changes on Mars.


Image of North Polar Cap layered terrain, courtesy of Malin Space Science Systems/NASA, from Mars Global Surveyor





Evidence for Liquid Water on Mars

With increased exploration of the Martian surface with improved technology on our current spacecraft, we see more and more evidence for liquid water flowing (in the past) on Mars' surface. Two examples are shown below.





Gullies that resemble river gullies on Earth:

Image courtesy of Malin Space Science Systems/NASA, from Mars Global Surveyor





Outflow patterns on the walls of the South Polar region:

Left: Viking context image. Right: image courtesy of Malin Space Science Systems/NASA, from Mars Global Surveyor





Runoff channels:





These runoff channels are actually on Earth! This image, taken from space, shows a region of Yemen, which is now a desert. This is evidence for climate changes that have occurred on Earth. After the last Ice Age, Yemen was a more temperate grassland. The climate is much more arid today.





Climate Change on Mars

We will now discuss the changes that occurred in the Martian climate. What happened to all of the water? We will use the article you read from Sky and Telescope, entitled "The Iceball Next Door," as a starting point for our discussion.





Break into groups of 3-5 people, and in 10 minutes, be prepared to discuss the following questions:

From "Taking a Global Inventory"

  1. What is the geologic evidence for liquid water on Mars?
  2. When did this water exist on Mars? (there may be more than one viewpoint)
From "Early Climate: Warm Versus Cold"
  1. If Mars used to be warm enough to have liquid rain, what happened to all that gas in the Mars atmosphere?
  2. Why do some people disagree with the "warm early Mars" hypothesis?
  3. How would a "cold early Mars" explain the geologic features we see today?
From "Where is the Missing Water?"
  1. What are some possibilities for where Mars' water went?
  2. Why is the idea of ground ice, or a "cryosphere," favored?
From "The Gullies"
  1. If the water is not tied up in Mar's cryosphere, what could cause the gullies seen in crater rims?
  2. Why do some people dislike this interpretation?
  3. What is another explanation for the formation of the gullies?
From "Follow the Water"
  1. Why are planetary scientists so keen on finding the "missing" water on Mars?
  2. What kinds of future investigations will shed light on this question?