- Astronomers measure distances between space objects using astronomical units.
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- Gravitational force keeps planets in orbit around the Sun.
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- Earth is the only inner planet that has a moon.
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- Venus is the hottest planet in the solar system.
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- The outer planets are also called the gas giants.
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- The atmospheres of Saturn and Jupiter are mainly water vapor.
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- Asteroids and comets are mainly rock and ice.
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- A meteoroid is a meteor that strikes Earth.
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