Unit II: The Terrestrial Planets Summarized

Read Seeds: Section 5.2

Lecture: The terrestrial planets are close to the Sun and therefore receive more solar energy than the jovian planets. The average daytime temperature on Mercury is 700 degrees. The hottest planet in the solar system, Venus, is 900 degrees. The high amount of solar energy received by the terrestrials has played an important role in the evolution of the inner solar system. They have low masses and high density (average density: 5.03 grams/cubic cm.). Their high density indicates that they are composed of heavy elements and are solid, rocky planets. Their high density and their slow rotational velocity help to explain why their low oblateness (def.) (average oblateness: .001). The low masses of the terrestrials accounts for their low escape velocities (def.) (average: 7.75 km/sec). This might explain why the terrestrial planets have thin (if any) atmospheres. Table 1: Terrestrial Atmospheres Mercury Venus Earth Mars None Carbon Dioxide Nitrogen Oxygen Carbon Dioxide The atmospheres (def.) of the terrestrial are of great interest for several reasons. They are much thinner than those of the jovian planets. They are composed of gasses which are atypical of the rest of the universe and solar system. They are composed of heavy elements (table 1), rather than hydrogen and helium. They also exhibit a lot of diversity. Mercury has no atmosphere. Venus and Mars have atmospheres composed of carbon dioxide (CO2); and the Earth has an atmosphere that is unique in the solar system. It has the only atmosphere capable of supporting life as we know it. On to the Jovian Planets... Complete these Self-check Questions: The Earth's atmosphere is composed of oxygen and nitrogen. It is more correct to say that it is composed of molecular oxygen and nitrogen. Most atoms have the tendency to bond with other atoms. Thus, it is rare to find single atoms of oxygen or nitrogen. The oxygen and nitrogen in the Earth's atmosphere is diatomic (def.), ) O2. Use this periodic table of elements to determine the molecular weight of of diatomic oxygen. (ans.)

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