Vocabulary: astronomical unit, dwarf planet, eccentricity, ellipse, gas giant, Kepler’s laws, orbit,
orbital radius, period, planet, solar system, terrestrial planet
Gizmo Warm-up
The Solar System Explorer Gizmo shows a model of the solar
system. All of the distances, but not the sizes of the planets, are
shown to scale. To begin, turn on Show orbital paths and click Play
( ). You are looking at the four inner planets.
1. In which direction do planets go around the Sun,
clockwise or counterclockwise?
counterclockwise
2. An orbit is the path of a body around another body.
What is the shape of the planetary orbits around the about orbital
Sun?
3. Click Pause ( ). You can see the name of each planet by holding your cursor over the
planet. What is the order of the eight planets, starting from the Sun? Click the “zoom out”
button ( ) to see the outer planets and Pluto, which is classified as a dwarf planet.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune
Activity A:
Get the Gizmo ready:
Classifying ● Click Reset ( ).
planets
Planets Classification
4. Gather data: Select Mercury from the Solar system menu at left. Turn on Additional data. In
the table below, record Mercury’s Mass, Mean radius, and Density. Then repeat for each of the
other planets as well as the dwarf planet Pluto. Include units.
Planet Mass (×1023 kg) Mean radius (km) Density (g/cm3)
Mercury 3.3×1023 kg 2440 km 5.427 g/cm3
Venus 48.7×1023 kg 6052 km 5.243 g/cm3
Earth 59.7×1023 kg 6378 km 5.515 g/cm3
Mars 6.4×1023 kg 3397 km 3.933 g/cm3
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, Jupiter 18,990×1023 kg 71490 km 1.326 g/cm3
Saturn 5680×1023 kg 60270 km 0.687 g/cm3
Uranus 869×1023 kg 25560 km 1.270 g/cm3
Neptune 1020×1023 kg 24760 km 1.638 g/cm3
Pluto (dwarf .1×1023 kg 1195 km 1.750 g/cm3
planet)
5. Analyze: What patterns do you notice in your data table?
inner planets have lower masses but higher densities while outer planets have
higher masses but lower densities
6. Summarize: Compare the masses, radii, and densities of the terrestrial planets and the gas
giants.
A. What do the terrestrial planets have in they are all low in mass but high
common? in density
B. the gas giants have in common? they are all high in mass but low
in density
7. Extend your thinking:
Why doesn’t Pluto fit into either the terrestrial Pluto has too small of a mass to
planet group or the gas giant group? be a gas giant and too small a
density to be a terrestrial planet
8. Think and discuss: Why do you think the inner planets are small and dense, while the outer
planets are gas giants?
I think the inner planets are dense and small because since they’re closer to the
sun, they are more affected by gravity which makes them compact as much as
possible, while the outer planets are still held together by gravity but not as much
since they’re so far away.
Get the Gizmo ready:
Activity B:
● Click Reset.
Planetary orbits ● Click the “zoom in” button ( ) several
times to zoom in as far as possible.
Introduction: Johannes Kepler (1571–1630) was a German astronomer who spent years poring
over a vast store of planetary data compiled by his predecessor, Tycho Brahe. After many
incorrect theories and other setbacks, Kepler at last determined the beautifully simple physical
laws that govern orbiting bodies. These rules are now known as Kepler’s laws.
Kepler’s laws: Rules to describe the size and shape of planetary orbits?
Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All
rights reserved