Any comments or questions about the material on this page should be directed to joe@nova.stanford.edu.

Questions

1. Using the graphical display tools on this site, generate a graph of the martian surface temperatures recorded by the MGS Radio Science Team. Also, generate a graph of the surface temperatures on Earth recorded by your class or one of the other participating classes in the outreach program (for example, CA0001). If possible, make hard copies of the surface temperature graphs for Mars and one location on Earth.
   • What (approximately) were the three lowest and three highest temperatures recorded on Mars?

   • What (approximately) were the three lowest and three highest temperatures recorded by one of the participating classes on Earth?

   • Based on the high and low temperatures from both Earth and Mars, which planet would you say is the warmer of the two?

   • Give two reasons why one planet is warmer than the other.

   • Based on the range of temperatures observed on Mars, how easy or difficult would it be for life as we know it to survive on the martian surface?

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2. Use the graphical display tools again to generate graphs of the solar longitude (season) and the sub-solar latitude at the time of the atmospheric measurements. The solar longitude is given in units of degrees, where (in the northern hemisphere) 0 degrees in the vernal equinox (first day of spring), 90 degrees is the summer solstice (first day of summer), 180 degrees is the autumnal equinox (first day of autumn) and 270 degrees is the winter solstice (first day of winter). The sub-solar latitude is the latitude of the point on Mars at which the sun is directly overhead. The sub-solar latitude, of course, changes with the seasons. At the two equinoxes, the sub-solar latitude is 0 degrees which means that the Sun is directly overhead at the equator. Make hard copies of the graphs if possible.
   • On what day (approximately) was the solar longitude on Mars equal to 270 degrees?

   • What season began on that day in the northern hemisphere of Mars?

   • What season began on that day in the southern hemisphere of Mars?

   • Why are the seasons different in the northern and southern hemispheres of Earth and Mars?

   • On what day (approximately) did the sub-solar latitude on Mars reach a minimum?

   • Do you think that it is a coincidence that the sub-solar latitude reaches a minimum on the same day that the solar longitude is 270 degrees? Why or why not?

   • How many degrees is Mars tilted relative to the plane in which it orbits the Sun?

   • What do you think is the sub-solar latitude on Earth when our solar longitude is 270 degrees? 90 degrees? 0 degrees?

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3. Use the graphical display tools again to generate graphs of the local time and latitude of the martian atmospheric measurements. Again, make hard copies of the graphs if possible.
   • What (approximately) was the local time on mars of the first martian atmospheric measurement and what what the local time near the peak in recorded martian surface temperatures at the beginning of April?

   • What (approximately) was the latitude of the first martian atmospheric measurement and what was the latitude near the peak in recorded martian surface temperatures at the beginning of April?

   • This question is not easy but very important! What season was it on Mars at the time and place that the first martian atmospheric measurement was recorded, and what season was it at the time and place of the measurements recorded near the peak surface temperature at the beginning of April? Don't forget that the season in the southern hemisphere is different than that in the northern hemisphere!

   • Based on differences in local time, latitude and season, explain why there is such a large variation in the martian surface temperatures recorded at the end of January and the beginning of April, 1998.

   • What is the typical surface temperature for your location at the same time of day and in the same season that the first martian atmospheric measurement was recorded?

   • What is the typical surface temperature for your location at the same time of day and in the same season that the peak martian surface temperatures were recorded at the beginning of April?

   • How and why does surface temperature vary over the course of a day?

   • How and why does surface temperature vary with latitude?

   • How and why does surface temperature vary with the seasons?

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4. The next questions concern a phenomenon which exists on Mars but does not exist on Earth! Observe closely the surface temperatures on Mars from the peak near the beginning of April 1 until the final measurements in the middle of April, 1998.
   • Describe the trend in martian surface temperatures over that two-week period.

   • Does the change in the local time of the measurements explain the trend in the martian surface temperatures?

   • Does the change in the season explain the trend in the martian surface temperatures?

   • Does the change in the latitude of the measurements explain the trend in the martian surface temperatures?

   • The last question was actually a trick question! As one moved toward lower latitudes on Earth in the summer, he or she would expect that the temperatures would increase and not decrease. The situation is different in summer in the southern hemisphere of Mars, however! The temperatures there increase as one moves poleward in the southern summer because Mars has very little cloud cover to reflect sunlight and the days are longer at the higher latitudes than they are at the lower latitudes. Also, Mars has no bodies of water at the surface to slow the rate at which the planet heats up and cools down.

     Why do the higher latitudes have longer days in summer than the lower latitudes?

   • Why does the absence of cloud cover allow the surface to heat up more than it otherwise would when the days are long?

   • Why does the proximity to large bodies of water (on Earth!)affect surface heating and cooling?

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5. Using the graphical display tools on this site, generate graphs of the martian surface pressures recorded by the MGS Radio Science Team and the elevation of the surface at each of the measurement points with respect to martian "sea level". Also, generate a graph of the surface pressures on Earth recorded by your class or one of the other participating classes in the outreach program (for example, CA0001). If possible, make hard copies of the surface pressure graphs for Mars and one location on Earth.
   • Why is there a difference between the actual surface pressure measurements from Mars (blue curve on graph of martian surface pressure) and the estimated pressures at martian sea level (red curve)?

   • Does pressure increase or decrease when elevation increases?

   • Why does pressure change as it does with elevation?

   • Take a look at the atmospheric pressure profiles which the MGS Radio Science Team has posted, and make a hard copy of one of them if possible. Does the atmospheric pressure in the profile vary with elevation as you just said that it should? By what approximate factor does the pressure change with every 10 kilometer increase in altitude (be careful, the pressure is shown in the profiles on a logarithmic scale!)?

   • Based on the graph of martian surface pressure, what is the (approximate) average pressure at "sea level" on Mars?

   • Based on the graph of surface pressure from your class or one of the other participating classes in the outreach program, what is the (approximate) average atmospheric pressure at sea level on Earth?

   • Is the average sea level pressure higher on Earth or on Mars? How many times larger is it?

   • Give two reasons why the pressure on Earth is so much different than it is on Mars?

   • Can you explain why water cannot exist in liquid form on Mars? Is it at all related to the fact that the boiling point of water on Earth decreases when elevation increases?

   • Can you explain why the martian atmosphere does not effectively filter the ultraviolet rays from the Sun, and why those rays could be deadly for visitors (or existing life forms!) on the martian surface?

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6. The next group of questions concern a very interesting martian atmospheric phenomenon which also does not occur on Earth. The martian atmosphere is composed primarily of carbon dioxide. During winter, a significant fraction of the global carbon dioxide freezes out of the atmosphere onto the polar cap in the winter hemisphere. Atmospheric pressure decreases at this time. Atmospheric pressure then increases during the spring in each hemisphere as carbon dioxide sublimates (changes state from solid to gas) back into the atmosphere.
   • Describe the trend in the estimates of martian surface pressure at the martian "sea level" (red curve of graph of martian atmospheric pressures).

   • On what (approximate) date do the pressures at the martian "sea level" appear to begin to decrease?

   • How does this date compare to the date of the winter solstice in the northern martian hemisphere?

   • By what (approximate) percentage does the pressure at the martian "sea level" change from the time when it begins to decrease to the end of the MGS Radio Science Team recording period in the middle of April, 1998?

   • Why does the "sea level" pressure change during this period?

   • What percentage of the atmosphere is deposited on the winter (north) polar cap during this period?

   • Using the graph of solar longitude at the time of the martian atmospheric measurements, estimate the date on which spring will begin in the northern martian hemisphere. Then, estimate what the atmospheric pressure will be at martian "sea level" on that date. What percentage of the carbon dioxide in the martian atmosphere will be deposited on the north martian pole by the end of the northern winter?

   • When carbon dioxide is transfered from the martian atmosphere to one of the martian poles, the planet actually rotates slightly faster! When the frozen carbon dioxide sublimates back into the atmosphere, the planet rotates more slowly again. Explain this phenomenon if you can!