formation of the sun and planets

formation of the solar system

The most widely accepted explanation of how the solar system formed is called the nebular hypothesis. According to this hypothesis, the Sun and the planets of our solar system formed about 4.6 billion years ago from the collapse of a giant cloud of gas and dust, called a nebula. The nebula was drawn together by gravity, which released gravitational potential energy. As small particles of dust and gas smashed together to create larger ones, they released kinetic energy. As the nebula collapsed, the gravity at the center increased and the cloud started to spin because of its angular momentum. As it collapsed further, the spinning got faster, much as an ice skater spins faster when he pulls his arms to his sides during a spin. Much of the clouds mass migrated to its center but the rest of the material flattened out in an enormous disk. The disk contained hydrogen and helium, along with heavier elements and even simple organic molecules.

formation of the sun and planets

As gravity pulled matter into the center of the disk, the density and pressure at the center became intense. When the pressure in the center of the disk was high enough, nuclear fusion began. A star was bornthe Sun. The burning star stopped the disk from collapsing further. Meanwhile, the outer parts of the disk were cooling off. Matter condensed from the cloud and small pieces of dust started clumping together. These clumps collided and combined with other clumps. Larger clumps, called An artists painting of a protoplanetary disk. planetesimals, attracted smaller clumps with their gravity. Gravity at the center of the disk attracted heavier particles, such as rock and metal and lighter particles remained further out in the disk. Eventually, the planetesimals formed protoplanets, which grew to become the planets and moons that we find in our solar system today. Because of the gravitational sorting of material, the inner planets Mercury, Venus, Earth, and Mars formed from dense rock and metal. The outer planets Jupiter, Saturn, Uranus and Neptune condensed farther from the Sun from lighter materials such as hydrogen, helium, water, ammonia, and methane. Out by Jupiter and beyond, where its very cold, these materials form solid particles. The nebular hypothesis was designed to explain some of the basic features of the solar system: The orbits of the planets lie in nearly the same plane with the Sun at the center The planets revolve in the same direction The planets mostly rotate in the same direction The axes of rotation of the planets are mostly nearly perpendicular to the orbital plane The oldest moon rocks are 4.5 billion years Click image to the left or use the URL below. URL:


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the solar system formed nearly ___ years ago

a) 100 billion

b) 5 million

-->  c) 5 billion

d) 3 thousand

the major bodies of the solar system formed

a) at the same time.

-->  b) in this order: sun, inner planets, outer planets, asteroids, comets.

c) in this order: asteroids, comets, sun, outer planets, inner planets.

d) from a black hole.

a nebula is

a) a newly formed star

b) the material that was left over from the big bang

-->  c) a giant cloud of dust and gas

d) none of these

the nebular was drawn together by gravity, which released kinetic energy.

a) true

-->  b) false

the sun formed in the center of the nebula because

a) most of the clouds mass migrated to the center.

b) the density at the center was extreme.

c) hydrogen and helium were present and nuclear fusion began.

-->  d) all of these.

the planets formed because

-->  a) clumps of material continued to collide due to gravity.

b) the burning sun flung molten material off into orbit.

c) solid material precipitated out of the gases that orbited the sun.

d) none of these.

the planets are sorted by density outward from the sun because of

a) centrifugal force

b) angular momentum

c) the planetary orbits

-->  d) gravity

the inner planets are made primarily of

-->  a) dense rock and metal.

b) gases and ices.

c) hydrogen, helium, water, ammonia and methane.

d) all of the above

the nebular hypothesis explains why

a) the planets orbit the sun in different planes.

-->  b) the oldest rocks scientists have dated are about the same age.

c) half the planets revolve clockwise and half the opposite.

d) all of these.

materials that on earth are liquids or gases are solids in the outer planets.

-->  a) true

b) false

diagram questions

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