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To MARS with MER - Educators Activity 6 Mission Planning: Earth/Mars Comparisons

Teacher Background
The Mars Exploration Rovers will be sending back huge amounts of new images and data to NASA JPL, much of which will be made available not only to scientists, but to students via television, print, and the Internet. For students to understand this data, they need some basic background about what is already known about Mars. A good way to make this information interesting is to compare and contrast conditions on Mars to those on our own planet and/or evident in students' local or regional environments. The next two Activities are intended to both engage and inform students. (See Student Worksheet for basic Earth/Mars data.)

Atmosphere and Hydrosphere

Abundant liquid water is what makes our home planet unique in the solar system. Approximately three quarters of Earth's surface is covered by it. Some of this water evaporates and condenses around dust, salt, or pollen grains that are blown into the atmosphere, and these condensation nuclei are the beginnings of clouds. Clouds produce rain and snow and help trap the heat energy that's radiating back from Earth's surface. Carbon dioxide also helps keep heat in the atmosphere-which is known as the greenhouse effect. Clouds and carbon dioxide help moderate the daily temperature fluctuations on Earth, which are at their most extreme in deserts where there is very little water vapor or clouds to trap heat.

The atmosphere of Mars contains very little water. Conditions on Mars are far too dry for extensive water clouds to form, but even this little amount can condense, forming high, thin, wispy clouds. Early morning fog collects in valleys, and frosts may form on the ground, but these rapidly dissipate as the morning temperature rises. Since Mars is so cold, water is in the form of ice crystals.

The Martian atmosphere is too thin (equivalent to 100,000 feet altitude on Earth) for carbon dioxide to hold in infrared radiant energy and so it has no greenhouse effect as here on Earth. Mars is heated only by the incoming solar radiation, and thus is subject to great day-night fluctuations in temperature.

Storms on Mars are not rain storms as on Earth, but rather dust storms. These occur when the southern hemisphere on Mars is in summer. These dust clouds trap infrared energy and keep it from escaping back into space and so help make Mars' atmosphere a little warmer. (See MarsWatch for why dust storms are of great interest to NASA's Mission Planners.)

Days and Seasons

The rate of spin of a planet (its rotation on its axis) determines the length of its day-night cycle. Earth takes 24 hours to make one complete rotation, which we call a "day". Mars takes 24 hours and 37 minutes, which scientists call a "sol". If you were on Mars, you'd sense a day-night cycle similar to that on Earth. Sojourner's baseline mission is 7 sols, though scientists certainly hope it will survive much longer.

The tilt of a planet's axis (relative to its orbit) determines whether or not the planet has seasons and, if so, how severe they might be. Earth's axis is tilted 23 1/2 degrees, and Mars about 25 degrees. Mars, just like Earth, has seasons. MPF will land on July 4, summer in Earth's northern hemisphere and summer at the planned Ares Vallis landing site on Mars.

The distance of a planet from the Sun and the nature of its atmosphere also has a large effect on its weather and climate. Mars is almost one and a half times as far from the Sun as Earth is, and takes about twice as long to travel around the Sun. (A planet's revolution around the Sun determines its year.) Consequently, Mars is colder than Earth and its seasons last about twice as long as ours.

As students will soon discover, however, evidence written in surface channels on Mars, and inferred from its giant volcanoes, make most scientists pretty certain Mars was once quite different, with liquid water on its surface and a thicker atmosphere protecting it from destructive radiation. (See Activities 1.3 and 2.2) Now Mars is cold and dry; its surface too cold for life and scoured by incoming UV rays. One key and fascinating question that will take many missions over many years to answer is whether life-dependent on water and a more clement climate-once existed on Mars?


 • Students will compare and contrast key characteristics which make Mars similar to, and different from, Earth.

 • Student will demonstrate the ability to use appropriate research skills to gather factual data about Mars and Earth.


 • Student Worksheet
 • atlases
 • globes
 • encyclopedias (book, CD-ROM or online)
 • online access
 • paper
 • pencil


"Approximately 3.8 billion years ago, Mars and Earth are believed to have been very similar. Understanding what happened to Mars may help us understand our own planet and its future."
- NASA life scientist Chris McKay, Washington, DC, July 1996

Ask students to brainstorm a list of physical features on Earth. When they are finished, ask them to place a check-mark next to each physical feature they already know can also be found on Mars. Ask students in what ways knowledge about the Martian environment is important to mission scientists. Explain that in this Activity, they'll be simulating the role of the researchers at NASA and JPL.



1. Organize students into Mission Teams of 3 or 4 students. Their assignment is to research and organize basic data necessary for mission planning. Encourage them to brainstorm team strengths and skills and make decisions about the best cooperative plan for data acquisition. (Be sure each team has solid plans and procedures.)
2. Complete research in teams. Compare data tables with other research teams; discuss any differences, and come up with the most comprehensive Class Data sheet you have time, or wall space, to accommodate.

Student Worksheet Answer Key in Word Format

Student Worksheet Answer Key in Adobe Acrobat Format

Suggested URLs
The Nine Planets

Views of the Solar System

Solar System Exploration