Universe Cycle - Solar System (5)
Post Lab 

   
OBJECTIVES:
  • Discovering the atmosphere on different planets.
  • Interpreting data on atmosphere.
VOCABULARY:
  • atmosphere
  • carbon dioxide
  • helium
  • hydrogen
  • Solar System
MATERIALS:
  • worksheet

Students take notes on a data sheet.

BACKGROUND:

An atmosphere is the layer of gases that envelop a planet. On the Earth, it is this envelope that allows organisms to live. Atmospheric ozone protects us from ultraviolet radiation. CO2 and other gases trap heat and keep the surface warm enough for life to thrive. Oxygen has allowed life to evolve.

Each of the planets has a different atmosphere, although there are clear similarities between the atmospheres of the four terrestrial planets and the four gas giant planets. The terrestrial planets are rich in heavier gases and gaseous compounds, such as carbon dioxide, nitrogen, oxygen, ozone, and argon. In contrast, the gas giant atmospheres are composed mostly of hydrogen and helium.

The atmospheres of at least the inner planets has evolved since they formed. This is clearest for the Earth. The Earthís original atmosphere was probably similar to Venus in composition, consisting of carbon dioxide and nitrogen. The evolution of photosynthesis converted carbon dioxide in the Earthís atmosphere to oxygen, increasing the amount of O2 in it from an initial 0.01% to its current 22% level.

Here is basic information on the atmosphere of each planet to guide your Post Lab discussion. Mercury has a very thin, almost undetectable atmosphere composed of sodium and potassium gas. These elements were likely blown from the surface of Mercury by the solar wind.

The atmosphere of Venus is composed mainly of carbon dioxide with minor amounts of nitrogen and trace amounts of nitrogen, helium, neon, and argon.

The Earth's atmosphere primarily composed of nitrogen and oxygen. Minor gases include and carbon dioxide, ozone, argon, and helium.

Mars' atmosphere is a thin layer composed mainly of carbon dioxide. Nitrogen, argon, and small traces of oxygen and water vapor are also present.

Jupiter's atmosphere contains mainly helium and hydrogen with trace amounts of water, ammonia, methane, and other carbon compounds. Three layers of clouds may exist in Jupiterís outermost atmosphere. The lowest are made of water ice or droplets, the next are crystals of a compound of ammonia and hydrogen sulfide, and the highest clouds are ammonia ice. There seems to be no solid surface under the atmosphere, only a transition from gas to liquid metallic hydrogen. In the top one-fourth of the planet, the pressure and temperature are so high that the hydrogen atoms are stripped of their outer electrons, forming a liquid metal.

Like Jupiter, Saturn has a thick atmosphere composed of hydrogen and helium. The ratio of hydrogen to helium ratio decreases with depth. Methane and ammonia are also present. The atmosphere of Saturn envelops a thick layer of metallic hydrogen.

Uranus' atmosphere is composed mainly of hydrogen and minor amounts of helium Methane is present in minor amounts, and probably forms most of the clouds seen by space probes and telescopes. Uranus and Neptune both appear blue because methane strongly absorbs light of other wavelengths.

The atmosphere of Neptune consists mainly of hydrogen and helium, but about 2.5-3% of the atmosphere is methane. Like Uranus, clouds in Neptune's atmosphere are composed of crystals of methane.

Pluto's atmosphere seems to be very thin, and is likely composed of nitrogen and carbon dioxide.

Note that none of the other planets or moons in the Solar System have atmospheres similar to the Earth. This means that if humans travel to other bodies, they will have to bring their own atmosphere in order to survive.

PROCEDURE:
  1. Present the information on planetary atmospheres discussed in the Background with your students. Have them fill out the worksheet as you talk. If you write the information on the board, you may want to use chemical notation as a shorthand.
     
  2. After the students record this information, have them compare and contrast the different atmospheres. They should observe that the inner planets all have nitrogen and carbon dioxide, except for Mercury. They should note that the gas giant planets have abundant helium, hydrogen and methane. You may wish to explain that planetary atmospheres have changed through time, using the Earth as an example.

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