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Planets of the Solar System Section 1 The Formation of the Solar System ISN pg. 69 Planets of the Solar System Section 1 What is the solar system? solar system the sun and all of the planets and other bodies that travel around it Planets of the Solar System Section 1 A planet is a celestial body that orbits the sun, is round because of its own gravity, and has cleared the neighborhood around its orbital path In the 1600s and 1700s, many scientists thought that the sun formed first and threw off the materials that later formed the planets. This was incorrect. Planets of the Solar System Who is Laplace? In 1796, French mathematician Pierre Simon, marquis de Laplace, advanced a hypothesis now known as the nebular hypothesis. Section 1 Planets of the Solar System Section 1 What is The Nebular Hypothesis? Laplace’s hypothesis states that the sun and the planets formed from an original nebula of gas and dust. Modern scientific calculations support this theory and help explain how the sun and planets formed from an original nebula of gas and dust. Planets of the Solar System Section 1 What is a solar nebula? solar nebula a rotating cloud of gas and dust from which a star, planets, and exoplanets form; this is how all solar systems begin. The sun is composed of about 99% of all of the matter that was contained in the solar nebula. Planets of the Solar System The Lagoon Nebula Section 1 Planets of the Solar System Section 1 How did the planets form? While the sun was forming in the center of the solar nebula, planets were forming in the outer regions. Planetesimal- a small body from which a planet originated in the early stages of development of the solar system Planets of the Solar System Section 1 How did the planets form? Some planetesimals joined together through collisions and through the force of gravity to form larger bodies called protoplanets. The protoplanets’ gravity attracted other planetesimals, which collided and added their masses to the protoplanets. Planets of the Solar System Section 1 How did the planets form?, continued Protoplanets became very large and condensed to form planets and moons. Moons are smaller bodies that orbit the planets. Planets and moons are smaller and denser than the protoplanets. Some protoplanets were massive enough to become round but not massive enough to clear away other objects near their orbits. These became the dwarf planets. Planets of the Solar System Section 1 Formation of the Planets, continued The diagram below shows the formation of the Solar System. Planets of the Solar System • http://youtu.be/-Ip5BAEfZuA Section 1 Planets of the Solar System Section 1 How did the Inner Planets form? The features of a newly formed planet depended on the distance between the protoplanet and developing sun. The four protoplanets that became Mercury, Venus, Earth, and Mars were close to the sun. Planets of the Solar System Section 1 How did the Inner Planets form? They contain large percentages of heavy elements, such as iron and nickel. At the temperature of the gases, gravity was not strong enough to hold their gases. Other lighter elements may have been blown or boiled away by radiation from the sun. The inner planets are smaller, rockier, and denser than the outer planets. Planets of the Solar System Section 1 How did the Outer Planets form? Four other protoplanets became Jupiter, Saturn, Uranus, and Neptune. These outer planets formed in the colder regions of the solar nebula far from the sun. Because they were cold, they did not lose their lighter elements, such as helium and hydrogen, or their ices, such as water ice, methane ice, and ammonia ice. Planets of the Solar System Section 1 How did the Outer Planets form? The intense heat and pressure in the planets’ interiors melted the ices to form layers of liquids and gases. These planets are referred to as gas giants because they are composed mostly of gases, have low density, and are huge planets. Uranus and Neptune are sometimes called ice giants. Planets of the Solar System Section 1 Formation of the Planets, continued Pluto-The First Dwarf Planet • From its discovery in 1930, Pluto was known as the ninth planet. It is quite unlike the other outer planets, which are gas giants or ice giants. • Pluto is very cold and may be best described as an ice ball that is made of frozen gases and rocks. • Because of its characteristics, many astronomers disagreed with Pluto’s classification as a planet. • In 2006, astronomers redefined the term planet and reclassified Pluto as a dwarf planet. Planets of the Solar System Section 1 Formation of Solid Earth Early Solid Earth • When Earth first formed, it was very hot. • In a process called differentiation, denser materials sank to the center, and less dense materials were forced to the outer layers. • At the center is a dense core that is composed mostly of iron and nickel. • Around the core is a the very thick layer of iron- and magnesium-rich rock called the mantle. • The outermost layer of Earth is a thin crust of less dense, silica-rich rock. Planets of the Solar System Section 1 Formation of Solid Earth, continued Present Solid Earth • Eventually, Earth’s surface cooled enough for solid rock to form from less dense elements that were pushed toward the surface during differentiation. • Earth’s surface continued to change as a result of heat in Earth’s interior as well as through impacts and through interactions with the newly forming atmosphere. Planets of the Solar System Section 1 Formation of Solid Earth, continued The diagram below shows the differentiation of Earth.