Live From Mars was active July 1996-December 1997.
Teacher Background: Seasons, weather and climate on Earth and Mars
The primary influence on Earth's seasonal temperature changes arises from
the fact that its axis of rotation (its daily spin on an imaginary North
Pole/South Pole line) is tilted relative to the plane of its orbit (its
yearly path around the Sun). This tilt amounts to about 23 and a half
Mars' axis of rotation is also tilted to the plane of its orbit: about 25 degrees (almost the same as Earth). Thus, Mars also has seasons. As on Earth, scientists call these seasons summer, fall, winter and spring with opposite seasons occurring simultaneously in the northern and southern hemispheres. However, since Mars takes almost twice as long to go around the sun as does Earth, its seasons are almost twice as long as ours.
The Earth is actually closest to the Sun in early January and farthest from the Sun in early July. However, Earth's orbit is so close to circular that the tilt of our planet's axis has far more to do with temperature differences from summer to winter than our planet's distance from the Sun. Mars' orbit is considerably more elliptical than Earth's. Mars' distance from the Sun varies from as little as approximately 128 million miles (207 million kilometers) to as much as about 154 million miles (249 million kilometers). Thus, at times, Mars is about 20% closer to the Sun than at other times and this changing distance from the Sun also significantly influences its seasons.
Because a planet travels fastest around the Sun when it is closest to it and slowest when it is farthest away, this also has an effect on the length of the seasons in the different hemispheres. During the current epoch, Mars is closest to the Sun when it's summer in the southern hemisphere. Thus, southern hemisphere summers on Mars are currently shorter but warmer than those in the northern hemisphere, while northern hemisphere winters are shorter but colder than those in the southern hemisphere. Southern hemisphere summer temperatures can be as much as 60°F degrees (33°C) warmer than those in the northern hemisphere.
Because Mars is farther from the Sun than Earth, its average seasonal temperatures are, as you would imagine, colder than on earth. Mars has an atmosphere that's mostly carbon dioxide. This creates a greenhouse effect, but because the atmosphere is so thin, the resulting increase in global temperature is only about 5 to 10 degrees. Overall, Mars is much colder than Earth.
On a warm summer afternoon, near the Martian equator, the surface temperature can occasionally climb to 65° F (18°C). Even a few centimeters above the surface, however, temperatures are lower. And at this same spot, the temperature at sunset will have dropped to below freezing and during the night the thermometer will plunge to more than 100 degrees below zero F. Around Mars' Northern polar cap, during the long winter nights, temperatures can fall to as much as 200 degrees below zero F!
Normally, the thin Martian atmosphere is clear and the planet's surface can be easily seen. Occasionally, there are clouds. The white or blue-white clouds are composed of H2O ice crystals or, more commonly, carbon dioxide ice crystals. These can be seen around the summits of Mars' huge, extinct volcanoes, along the sunrise limb of the planet or in the canyons. Yellowish clouds are the result of fine grains of Martian desert dust being blown into the air. Occasionally, especially when warm summers come to the Southern hemisphere, giant dust storms spread to cover most of the planet for weeks in billowing clouds that are several miles high.
Martian surface winds are normally quite light (between about 4 and 15 miles per hour [6.5Ð24 km/hour]). On occasion, however, surface winds gust to about 50 miles (80 km) per hour and, during dust storms can blow at over 300 miles (480 km) per hour. Because the Martian atmosphere is so thin, however, you would feel much less pressure from the wind than if you stood in a similar speed wind on earth.
Light frosts do occur on Mars and light snows may occasionally fall, but most of the build up in the Martian polar caps during the winter months is due to direct condensation of H2O and carbon dioxide out of the atmosphere.
The Martian Sun Times|
An interesting multidisci-
Skills involved include
Activity I: Seasons on
Activity II: Today on Mars
Activity III: Atmospheric
Activity IV: Probing Earth:
The project, developed at
tained in the Teacher Materials)
Engage Ask students about temperature and wind. What is the hottest they can ever remember it being in their town? The coldest? What's the average wind speed? How high are wind speeds in a hurricane? A tornado?
Explore/Explain Explain to the students that they will research temperature and wind conditions on Earth and then compare these to our neighbor world, Mars.
If your school has a weather station, ask students to make daily records of maximum and minimum temperatures and the relative humidity over the course of a couple of weeks. If your school has the necessary equipment, have students record the average and peak wind speeds as well. If your school (or another school in your area) has kept such records over the past year, have students access these records and examine them. From this data or other sources such as the weather office at a local TV or radio station, The Weather Channel, the National Weather Service or the World Almanac, ask them to research the average daytime high and nightime low temperature records in their area for each month of the year, as well as the all-time high and low temperature records for their state, the country and the world.
Ask students to examine the average high and low temperatures in their area at different times of the year (especially summer and winter). Ask them to consider the length of day and night and the height of the sun in the sky, but also such factors as relative humidity, elevation, wind direction, ocean influences, etc. Tell students to research the average high and low temperatures in January and July in San Francisco, Miami, Rio de Janeiro, Quito, Riyadh, Jakarta and Sydney. Have them post these temperatures on their world map. How do these temperatures and day-night temperature differences vary with latitude? Consider other factors such as distance from equator, elevation, tropical or desert environment, or ocean influences.
Next turn students' attention to Mars. Have students access Viking-based Mars temperature data from the Web, or give teams copies of the temperature data sheets in your Teacher Materials. After helping students become familiar with these temperature maps, have them compare these maps to the surface features of Mars. Ask them to make tables (on paper, or as computer spreadsheets) of the average daytime high and nightime low temperatures during summer and winter on Mars, for latitudes at 45 and 80 degrees north and south latitude by averaging temperatures at longitudes of 0, 90, 180 and 270 degrees. Next, have students compute the difference between daytime highs and nightime lows for each of these locations. Challenge them to explain the temperatures and day-night temperature differences that they observe. Have them compare the maximum and minimum temperatures they observe on Mars with the temperature records for their city, state, country and Earth as a whole.
Give students information about the average and peak winds on Mars and have them compare these to average winds in their area. Compare the wind speeds in Martian dust storms with the winds in such terrestrial storms as hurricanes and tornadoes.
|Note: The primary landing site on Mars for the Pathfinder spacecraft is in the area of Ares Vallis, somewhere around latitude 20 degrees north and longitude 31 degrees at a time that will be late summer in Mars' northern hemisphere. Challenge your students to come up with a weather forecast for the date of the landing (July 4, 1997) for this landing site and a general temperature forecast for the next six months on Mars (that is, through December 1997) for this location.|
Teachers can introduce the
formulas for converting Celsius to Fahrenheit and vice versa, as well as
kilometers per hour to miles per hour, and give their students practice
manipulating the algebraic equations.|
Teachers of students in higher grades can use this Activity to give students experience in graphing such variables as maximum temperature, minimum temperature and temperature difference against time or longitude, and superimposing graphs of Earth data with corresponding graphs from Mars.
Have teams of students research and prepare weather reports for different locations on Mars. Then with appropriate graphics and maps which they prepare themselves, have them deliver 3 to 5 minute"Team Coverage" weather reports from around the Red Planet for the latest edition of the"Interplanetary News Network" (which premiered with weathercasts for Pluto and Neptune during our previous Live from the Hubble Space Telescope Module). Suggest that a student report from both the North and South polar caps. Others can be stationed on top of Olympus Mons, and on the equatorial plains near Valles Marineris and in front of a monstrous dust storm heading their way. Videotape the broadcasts, and send us copies at PTK.
Tell students that they are meteorologists on board the first human mission to Mars and ask them to write excerpts from their Weather Log compiled over a year's stay on the surface of the Red Planet. Students could either stay where they landed, or ask them to imagine that their team has been equipped with a special roving vehicle that will allow them to travel to the exotic locations to be found all over Mars.
Real Science, Real
In late 1997 and more especially on through 1998, Mars Global Observer
will also provide weather information, along with global imagery,
topographic mapping and soil and rock profiles. Here's what the MGS Radio
Science team at Stanford University intend: |
The MGS Radio Science Team will employ a technique called radio occultation to probe the Martian atmosphere. Twice per orbit, MGS will be occulted by Mars and an ultrastable radio transmission from the spacecraft to Earth will pass through and be perturbed by the thin atmosphere of Mars. (ed. As the spacecraft goes behind Mars and then emerges from behind the planet--"occultation"-- the radio signal returning to Earth will be affected by the varying amount and character of the Martian atmosphere through which it's being transmitted.) ...Analysis of the perturbations ...will yield profiles of the temperature and pressure of that atmosphere as a function of height above the planet's surface. Team members are hopeful that sophisticated inversion techniques which they are developing will permit the derivation of temperature and pressure profiles with a resolution of 10 meters!
The atmospheric profiles will provide the basis for the Daily Martian Weather Report which will be posted to this page (ed. note: see URL listing below) as raw data is collected and analyzed. Please come back and find out about the Martian climate, the atmospheric temperatures and pressures, the effects of Martian dust storms (massive temperature inversions), and the very interesting seasonal variations which occur as polar ice caps form and thaw.
How to access Real Science, Real Time
The Live From Mars Web site will provide updated links to all the weather data and imagery returning from both missions. It will also point to curriculum materials developed by the research teams who built and use the various instruments. Encouraging P.I.'s and their co-workers to engage directly in Education and Outreach is another innovative aspect of these missions. Just as with the Live from Mars project, it's a chance for your students to engage in Real Science, with Real Scientists.
To fully appreciate the significance of the MGS radio occultation measurements, think about this. If you were to launch a weather balloon from the surface of Mars, you would be able to measure the temperature and pressure at many heights as the balloon rose through the Martian atmosphere. You would essentially be able to collect one profile each of atmospheric temperature and pressure. Using the radio occultation technique, the MGS scientists have the potential to collect two of these sets of profiles for each orbit of the MGS spacecraft. With 12 orbits per day and 687 days in a Martian year, the Radio Science Team members may gather as much data on the Martian atmosphere as if they were able to release many thousands of weather balloons at various locations on the red planet and measure the temperature and pressure at 10 meter intervals above the Martian surface!