Unit II: The Terrestrial and Jovian Planets

Read Seeds: Section 5.2

Lecture: Eight of the nine planets fall into two distinctive categories. Mercury, Venus, Earth and Mars share similar properties and therefore are referred to as the terrestrial planets. Jupiter, Saturn, Uranus and Neptune share properties that are unique to them; therefore, they are referred to as the jovian planets. Pluto falls into a category of its own and is traditionally ignored when discussing the formation of the planets.

The properties of the planets are important in developing a theory which explains the origin of the solar system because any good theory would have to explain the origin of those properties. To better understand the differences between the terrestrial and jovian planets, use the printout of planetary data obtained from the Planetary Data Browser to do this activity. If you no longer have the printout refer to the Properties of the Solar System.

The spacing of the planets' orbits works out so that for most cases the next planet out is about twice as far as the previous planet. A specific numerical sequence was figured out by Johann Titius and popularized by Johann Bode in the late 1700's. A gap between Mars and Jupiter led astronomers to search for a missing planet. Instead they discovered asteroids in that region. Read up about the Titius-Bode Law.

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7. Search the Orbital Data Table. Cut and paste from the data table the information just about the nine planets: (2 points)
8. Using the search results in question seven, answer the following questions:
   a. What is the average eccentricity of the the orbits of the nine planets in our solar system? Which planet's orbit has the highest eccentricity? the lowest eccentricity? (2 points)
9. Using the solar system data generated in question seven, determine which three planets have a retrograde rotation (def.). Retrograde rotation is represented by a negative rotation period. (1 point)
10. Using the physical solar system data generated in question seven, calculate the average inclination for the orbital planes of the planets? Which two planets have orbits inclined at an angle greater than 4 degrees? (2 points)
11. What is the Titius-Bode Law? What is its significance to astronomy? (1 point)

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