The "Planet & Interior" section can directly used by students or presented by teachers. The cross-sectional diagrams of Earth and Jupiter can be used by students to compare the structure and size of a rocky inner planet and a gaseous outer planet.

The exercise to calculate the ABSOLUTE spin rate (at the bottom of the page) is rated:

The exercise to calculate the RELATIVE spin rate (at the bottom of the page) is rated:

# Planet Structure & Interior

The familiar brown, white and orange clouds that we can see on Jupiter make up only the thin outermost layer. Like every substance, the molecules and atoms in Jupiter's cloud tops emit and absorb radiation at certain characteristic wavelengths, just as a guitar string will vibrate only at given frequencies. The wavelengths that characterize individual chemicals are accurately known from laboratory experiments. Earth-based studies revealed that Jupiter's atmosphere is composed mainly of hydrogen with small amounts of ammonia and methane. There is also a significant amount of helium in the atmosphere; the ratio of hydrogen to helium is close to that found on the Sun!

Although Jupiter is extremely massive (1.9 X 1027 kg), its mean density is only 1.33 grams per cubic centimeter (slightly greater than water's density). The mean density of the Earth is about four times that of Jupiter! The large size and low density indicate that Jupiter is made up of lighter elements, in particular hydrogen and helium; these are present mainly in the form of gas and liquid.

# Q and H (for "hints")

Jupiter and the Earth spin in the same direction (counter-clockwise if you're looking down at the North Pole). Even though it doesn't feel like we're moving, we actually travel the distance around the Earth (its circumference if we're at the Equator) every day. If you were "sitting" on a cloud in Jupiter's atmosphere you'd move faster than you move "sitting" on the Earth's surface.

Q: One Jupiter day is 9 hrs 48 min. How much faster would you be moving on Jupiter than on Earth?

H: To know the ABSOLUTE rate you're moving you need to know two things about each planet: the length of its day and its circumference (2 X pi X R). To estimate the RELATIVE speed between Earth and Jupiter you simply need to know the following: Jupiter's day is about 2 1 / 2 times shorter than one Earth day. From page 3 we know that Jupiter's diameter is about 12 times that of Earth. Radius and circumference are LINEARLY related to diameter (no exponents used in the equations) thus Jupiter's circumference is also 12 times greater than Earth.

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