University of Michigan - Department of Astronomy

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updated: 04/19/2000


Martian Surface Features - A Global Study

Introduction and Directions

In this exercise you will study some of the large scale surface features and global characteristics of the planet Mars using photographs and information obtained by the Mariner 9 mission, which placed a spaceprobe in orbit around Mars in 1971. The large volume of data obtained, some 7300 photographs, allowed a map of Mars to be constructed with a resolution of about one kilometer. See Appendix A for important historical information concerning our remote exploration of Mars.

Step 1: Large Scale Features from Map Inspection

Warning:

DO NOT make any marks on the maps or photographs!!

The map that will be used is Map I-961, produced by the United States Geological Survey from detailed inspection of the Mariner 9 imagery. Although it is classified as a topographic map, it shows albedo features as well and will allow a direct comparison of the surface features and albedo features.

The map shows altitude changes as red contour lines which are marked in kilometers above a zero kilometer reference level. Thus a contour line marked "11" represents an altitude 11 km above "sea level" on Mars. Coordinate and scaling information are also given which allow investigation of the sizes and relative positions of a number of large scale features. Read the notes given on the map to familiarize yourself with some of its characteristics and then answer the questions on the data sheet.

Step 2: Analysis of Surface Features in Mariner 9 Photographs

In this section, we will investigate some surface features in more detail than could be done with the map alone. By inspecting some selected Mariner 9 photographs and correlating what we see into the overall picture by referring to the map, we can hopefully determine some basic properties of the present and past Martian environment. The captions given with each picture are from the NASA publication Mars as viewed from Mariner 9 and include the coordinates of the photograph and some background information about the photograph.

Some additional information about the Martian environment will be helpful in determining causes and inter-relationships between features you see in the photographs. At the heart of these inter-relationships is probably the presence of geological and tectonic activity. In comparing Earth and the Moon we see that Earth is very active geologically, with the relatively recent realization that an advanced type of tectonic activity (plate tectonics) is taking place. The Moon, on the other hand, seems quite dead at present, although there is evidence for some past primitive tectonic activity (extensional tectonics, i.e. faulting, doming, etc.). With Mars being intermediate in size between these two, it would seem reasonable that the amount of geological activity would be intermediate too. Exactly how active Mars is or was is for you to determine.

The presence of a number of large volcanic cones certainly implies past volcanic activity, but whether these volcanoes are presently active or not is unknown. (Note: geologically speaking, "presently" indicates "within the last several million years.") On Earth, it is thought that a primitive, very dense atmosphere was exhumed several billions of years ago and that the present atmosphere and oceans have evolved out of it. (Note: water was one of the chief components of this exhuming process, which is called "outgassing.") Extending this general picture to Mars, we might guess that the present Martian atmosphere has evolved from the original (denser?) atmosphere initially outgassed. Estimating the total outgassing on Mars is a tricky business because so many assumptions are involved, but it seems reasonable that a considerable amount of water was outgassed over Mars' history. Since this water is not readily apparent and since now the atmosphere is too cold and its pressure too low for liquid water to exist, one of the favorite hiding spots proposed is sub-surface permafrost deposits. The possible presence of these deposits and the possibility of a warmer, denser atmosphere in the past should be considered in the formation of some features.

The atmosphere itself must be considered as a dynamic force affecting the Martian environment as has been evidenced by the observations of dust storms in the past. (Can you imagine an entire planet embroiled in one massive dust storm?!) It is important to realize, though, that the Martian atmosphere is less than one percent of the density of the Earth's sea level atmosphere and that there are features millions and billions of years old which remain in recognizable condition (impact craters, for exampl. Therefore, we should probably think mostly of the atmosphere as an erosive, modifying agent rather than a feature- forming process (with one notable exception that you will hopefully discover).

Appendix B has further explanation of geologic features, and you should read this summary carefully before carrying out the lab exercise.

The obliquity of Mars and the length of its day are quite similar to Earth's and thus it has seasons like the Earth does. This is most visibly indicated by the alternate formation of north and south polar caps. These caps are made of carbon dioxide, which not so coincidentally happens to be the major constituent of the atmosphere. (There is a permanent cap also at the north pole which is made of water ice, but we will refer mostly to the carbon dioxide caps). From information sent back by the Viking landers for over a full Martian year, we know that a fair portion of the atmosphere (some estimates go as high as 1/3) freezes out at one pole or the other. During the Martian spring and autumn, the current cap melts and there is a rush of atmosphere toward the other pole where it again freezes out. Depending on the speed with which this occurs and the kind of terrain this rush of air traverses, a large amount of dust can be picked up and transferred from place to place. You should look for evidence of this and indications of systematic air movement in the photographs.

Questions and directions are on the worksheets and are divided into subsections; in each subsection, you will investigate a particular type of surface feature. You should use the photograph, caption, position on the map relative to other features, and background information to come to some conclusions about the formation and/or inter-relationships of the features to one another.

Remember: Have fun!!!