Computer Drawing of the equations used to model the Martian
 atmosphere in English Units.

A text only version of this slide is available which gives all of the flow equations.

The Martian atmosphere is an extremely thin sheet of gas, principally carbon dioxide, that extends from the surface of Mars to the edge of space. The Martian atmosphere is less dense than the Earth's atmosphere, but there are many similarities. Gravity holds the atmosphere to the Martian surface. And within the atmosphere, very complex chemical, thermodynamic, and fluid dynamics effects occur. The atmosphere is not uniform; fluid properties are constantly changing with time and place producing weather on Mars just like on Earth.

These variations extend upward from the surface of Mars. The sun heats the surface, and some of this heat goes into heating the gas near the surface. The heated gas is then diffused or convected up through the atmosphere. Thus, the gas temperature will be highest near the surface and decreases as altitude increases. The speed of sound depends on the temperature and also decreases with increasing altitude. As with the Earth, the pressure in the atmosphere decreases with altitude. The density of the atmosphere depends on both the temperature and the pressure through the equation of state and also decreases with increasing altitude.

Aerodynamic forces directly depend on the gas density. To help aircraft designers, it is useful to define a mathematical model of the atmosphere to capture the effects of altitude. The model shown here was developed from measurements of the Martian atmosphere made by the Mars Global Surveyor in April 1996. The information on the Martian atmosphere was gathered by Jonathon Donadee of Canfield (Ohio) Middle School during a cyber-mentoring program in 1999. The data was curve fit to produce equations by Dave Hiltner of St. John's Jesuit High School as part of a shadowing program in May 1999. The curve fits are given for English units. These curve fits are also available in metric units. The model has two parts: one for the lower atmosphere, in which temperature decreases with altitude, and one for the upper atmosphere, in which the temperature decreases at a different rate. In each part, the pressure and temperature are curve fit; and density is derived from the equation of state.

An interactive Java applet for this slide is also available. With the applet, you can change altitude and see the effects on pressure and temperature. You can also compare the Martian atmosphere to the atmosphere on Earth.

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byTom Benson
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