Did it Rain on Mars? Analysis of Valley Networks on Mars in an Intro Geo Course

Barbara J. Tewksbury
Hamilton College
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Students investigate the question of whether it might have rained on Mars by doing an activity based on an article by Hynek and Phillips (2003). Students do a simple drainage basin analysis based on Hynek and Phillips' maps, calculate drainage densities, and compare results to data for rain-fed arid regions on Earth.

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Intro geo, geomorphology, planetary geology.

Skills and concepts that students must have mastered

This activity assumes virtually no prior knowledge on the part of students. The instructor can easily provide appropriate background at the time of the activity on the Viking mission, on images obtained from orbit by the Mars Orbiter Camera, and on elevation data obtained with the Mars Orbiter Laser Altimeter.

How the activity is situated in the course


Content/concepts goals for this activity

To evaluate whether ancient Mars valley networks might have been produced by rainfall analyzing how similar they are to valley networks on Earth that we know are produced by rainfall. Students complete simple drainage basin analyses and compare their results with terrestrial data.

Higher order thinking skills goals for this activity

  • analysis of data
  • synthesis of data from a variety of sources
  • critical evaluation of pre-existing hypothesis
  • evaluation of uncertainties

Other skills goals for this activity

Description of the activity/assignment

Some of the Viking images sent back from Mars in the 1970s show tantalizing evidence of dendritic valley networks in some of the oldest terrains on the planet. One of the big questions ever since has been whether it might have rained early in Mars history.

One of the ways of deciding whether the Mars valley networks might have been produced by rainfall is to find out how similar they are to valley networks on Earth, which we know are produced by rainfall. The standard method for analyzing drainage basins is comparison of the number of drainage segments per square kilometer (drainage density) and how extensively branched the network is (stream order).

In this exercise, students calculate stream order for valley segments mapped by Hynek and Phillips (2003) using MOC/MOLA data. Students then use data on valley segment length and drainage basin area from Hynek and Phillips (2003) to calculate drainage density. They compare stream order and drainage density for the Mars site with similar calculations for areas on Earth and evaluate the question of whether valley networks on Mars might be consistent with rainfall on an early Mars, and what the uncertainties and limitations are in their conclusions.

Determining whether students have met the goals

Student written work on the assignment completed in class.

More information about assessment tools and techniques.

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Other Materials

Supporting references/URLs

Carr, M.H., 1995, The Martian drainage system and the origin of valley networks and fretted channels: Journal of Geophysical Research, v. 100, p. 7479-7507.

Carr, M.H. and Chuang, F.C., 1997, Martian drainage densities: Journal of Geophysical Research, v. 102, p. 9145-9152.

Hynek, Brian M. and Phillips, Roger J., 2003, New data reveal mature, integrated drainage systems on Mars indicative of past precipitation: Geology, v. 31, no. 9, p. 757-760.