Unit Three: Investigating Planets
Doing Science

4. Investigating the Atmospheres of Planets

Introduction:
The atmospheres of the planets are as varied and different as the planets themselves. Some are hot; some are cold. Some are thick, some are thin, and some are almost non-existent. Planetary atmospheres are made of different gases: some are mostly carbon dioxide, some are mostly nitrogen, and some are mostly hydrogen. Circulation and cloud patterns are different too. Why are the characteristics of atmospheres so different? Which ones could support life? In this Doing Science, you will do a comparative analysis of the atmospheres of some of the other planets and moons with Earth's.

Information about atmospheres come from quite different measurement techniques: images provide information about cloud patterns and circulation, spectroscopy gives information about composition, and satellites give information about temperature and pressure profiles. Consequently, information about atmospheres is scattered across the Internet. A few Web sites provide compendia of atmospheric data mixed in with other data:

National Space Science Data Center, Planets node at: http://nssdc.gsfc.nasa.gov/planetary/ Click on the planet name to get both numerical and image data.

NASA's Solar system Exploration at: http://sse.jpl.nasa.gov/planets/index.cfm Click on a planet to get both numerical and image data.

Views of the Solar System at: http://www.lpl.arizona.edu/outreach/origin/ Click on Introductions to get descriptions and numerical data; click on Photo Library to get images and short movies.

Directions:
Seven of the planets and one moon (Titan) have significant atmospheres. Search the above sites (and other that you may find) and for each object:

1. Collect individual images and animations/movies that show the characteristic clouds and circulation patterns. Images useful for making movies of clouds and circulation in Earth's atmosphere can be found at sites like: http://weather.unisys.com/satellite/index.html Select Infrared for day/night sequences and GOES East or GOES West for hemispherical images. Collect images each hour for several hours, or once a day for several weeks and open them in a program like ImageJ to make your own movie.
2. Compile data tables that include the gas composition, cloud composition, surface and cloud-top temperatures (temperature profiles if available), surface pressures, and typical wind velocities.

Your Report:
Choose one of the following summary project ideas:

1. Prepare a poster or PowerPoint presentation that compares the cloud and circulation patters on Earth with other planets. Show your animations of clouds on the different planets, and describe how the circulations are the same or different from Earth's. Compare wind velocities between the planets and make a graph of mean wind speed with planet rotation rate. Explain how the two may be connected.
2. Prepare a poster or PowerPoint presentation presenting your tables of comparative compositions, temperatures, etc. Group the planets by primary atmospheric composition and describe how they are different. Propose models as to how the different compositions came about. For example, why is oxygen an important gas in Earth's atmosphere, but not of any other?
3. Triton, Pluto, and Ganymede have very thin atmospheres called "exospheres" which are thinner than a good laboratory vacuum, yet thicker than the stray molecules of interplanetary space. Compile density, temperature and composition data for these objects and search the Internet for ideas as to the origins of these gases.
4. Comparisons of isotopic ratios of atmospheric gases on Earth and Mars provided the information necessary to convince scientists that certain meteorites came from Mars and not some other body. Search out the relevant information and make a poster or PowerPoint presentation showing how studying atmospheres led to one of the most extraordinary scientific results of recent times.