formatIon of Planets
F ormation P lanets
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Most scientists believe our solar system began to develop about 4.6 billion years ago. It probably started as a loose cloud of gas and dust. Scientists think that a force called gravity pulled parts of the cloud together into clumps. The clump squeezed so tightly together that it became hot. The cloud, called the solar nebula, changed shape into a spinning disk and grew even hotter. The largest clump eventually became the Sun. The planets caption caption caption caption caption caption caption caption
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developed from the remaining material of the cloud. The disk then began to cool down. Gases in the disk combined into solid objects. The solid objects combined into bigger objects and attracted more material in a process called accretion. Over time, much of the material clumped together into larger bodies called planetesimals. They eventually formed larger protoplanets, which developed into the planets. caption caption caption caption caption caption caption caption
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Scientists developed theories about the formation of the planets based on observations of the solar system. The interior of the solar nebula—a giant cloud of gas and dust—had hotter temperatures near the Sun than farther away from the center. Metals and rocks formed from the original cloud of gas and dust. These metal and rock objects formed the inner, rocky planets. Farther away from the hot center near the Sun, temperatures were cold enough for ice to form. The ice in the outer planets is made of substances such as caption caption caption caption caption caption caption caption
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water, carbon dioxide, and ammonia. The outer planets grew bigger because of the ice and attracted light elements like hydrogen and helium. These are the most common elements in the universe, so the outer planets were able to grow to large sizes. caption caption caption caption caption caption caption caption
Think About It The disk of gas spinning around the still-developing Sun formed the planets. Why do the planets in our solar system orbit in the same direction?
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Most scientists believe our solar system began to develop about 4.6 billion years ago. It probably started as a loose cloud of gas and dust. Scientists think that a force called gravity pulled parts of the cloud together into clumps. The clump squeezed so tightly together that it became hot. The cloud, called the solar nebula, changed shape into a spinning disk and grew even hotter. The largest clump eventually became the Sun. The planets caption caption caption caption caption caption caption caption
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developed from the remaining material of the cloud. The disk then began to cool down. Gases in the disk combined into solid objects. The solid objects combined into bigger objects and attracted more material in a process called accretion. Over time, much of the material clumped together into larger bodies called planetesimals. They eventually formed larger protoplanets, which developed into the planets. caption caption caption caption caption caption caption caption
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Scientists developed theories about the formation of the planets based on observations of the solar system. The interior of the solar nebula—a giant cloud of gas and dust—had hotter temperatures near the Sun than farther away from the center. Metals and rocks formed from the original cloud of gas and dust. These metal and rock objects formed the inner, rocky planets. Farther away from the hot center near the Sun, temperatures were cold enough for ice to form. The ice in the outer planets is made of substances such as caption caption caption caption caption caption caption caption
10
water, carbon dioxide, and ammonia. The outer planets grew bigger because of the ice and attracted light elements like hydrogen and helium. These are the most common elements in the universe, so the outer planets were able to grow to large sizes. caption caption caption caption caption caption caption caption
Think About It The disk of gas spinning around the still-developing Sun formed the planets. Why do the planets in our solar system orbit in the same direction?
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