| Question | Answer |
| What does the solar system contain? | the sun, planets, and all other bodies that revolve around the sun |
| What planets are characterized by solid rock with metallic cores, zero to two moons, and impact craters? | inner planets |
| Which principle states that each planet orbits the sun in a closed curve whose shape is determined by two foci? | Kepler’s law of ellipses |
| What are small bodies from which planets originated in the early stages of development of the solar system? | planetesimals |
| Which astronomer believed that planets revolve around the sun, but at different speeds and distances from it? | Copernicus |
| Which planets are characterized by massive size, relatively low density, thick atmospheres of helium and hydrogen, and rock and metal cores? | outer planets |
| Which law states the cube of the average distance of a planet from the sun is proportional to the square of its orbital period | Kepler’s law of periods |
| Name the principle that states equal areas are covered in equal amounts of time as an object orbits the sun. | nebular hypothesis |
| What is the name of the theory that explains how the sun and planets condensed at about the same time out of a rotating cloud of gas and dust? | differentiation |
| Which astronomer believed that planets move in epicycles as they move in larger circles around the Earth? | Ptolemy |
| the process by which Earth formed three distinct layers: a dense core of iron and nickel, a thick layer of iron- and magnesium-rich rock, and a thin crust of silica-rich rock | differentiation |
| The sun and all of the planets and other bodies that revolve around it make up the _______________________. | solar system |
| Celestial bodies that orbit the sun, such as Earth and Jupiter, are called ______________. | planets |
| In 1796, the French mathematician Pierre-Simon, marquis de Laplace, advanced the ____________________ to explain the origins of the solar system. | nebular hypothesis |
| Laplace’s hypothesis states that the sun and the planets condensed at about the same time out of a rotating cloud of dust and gas called a | nebula. |
| The rotating cloud of dust and gas from which our solar system is thought to have formed is called the | solar nebula. |
| Energy from collisions and pressure from gravity caused the center of the solar nebula to become | hotter and denser. |
| Which of the following formed when the temperature at the center of the nebula reached about 10,000,000°C and hydrogen fusion began? | the sun |
| How much of the matter that was contained in the solar nebula makes up the sun? | about 99% |
| Small bodies from which a planet originated in the early development of the solar system are called | planetesimals. |
| Some planetesimals joined together through collision and through the force of gravity to form larger bodies called | protoplanets. |
| The smaller bodies that orbit the planets are called | moons. |
| Why are Mercury, Venus, Earth, and Mars called the inner planets? | because they are closest to the sun |
| Why did the inner planets, which contained large percentages of heavy elements such as iron and nickel, lose their less dense gases? | the planet's gravity was not strong enough to hold the gases, which may have been boiled or blown away |
| How do the surfaces of the inner planets compare with that of Earth today? | similar to that of Earth today |
| How do the inner planets differ from the outer planets? | they are smaller rockier, and denser than the outer planets |
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