The solar system formed from a gravitational collapse of an interstellar gas. Most of the mass collected in the center forming the Sun, while the rest formed a protoplanetary disk to create the planets, moons, asteroids, ect.
close encounter hypothesis
Thought that planets were formed from blobs of gas that were pulled out of two stars passing. Created after the nebular theory, but discarded today.
What two elements did the big bang produce?
Hydrogen and helium.
Where did the other elements in the universe come from?
As planets died they released the other elements that they converted while alive. Even after 14 billion years only 2% of material by mass was not hydrogen or helium.
What caused the gravitational collapse? What kept it going?
Some shock wave such as an exploding supernova triggered it. Gravity then continued the collapse.
How did heating, spinning and flatening affect the cloud.
Heating - temperature increased as the cloud collapsed. Colliding particles created thermal energy. Potential gravity -> kinetic energy of particles. Energy conversion
Spinning - the nebula spun faster as the cloud shrank (conservation of angular momentum). Greater the angular momentum, the more spread out it would be.
Flattening - random collisions of particles caused their orbits to become more orderly and circular.
What is accretion?
Individual particles traveling at same nearly equal speeds collided with each other an were held together by static electricity.
As they grew in mass gravity accelerated the process forming boulders known as planetesimals.
What ended planet formation?
Solar wind drove nebular gas out of the solar system.
The Sun rotates slower today cause its magnetic field dragged charged particles faster than the rest of the nebula. As the particles gained angular momentum, the Sun lost it.
What is heavy bombardment?
Occurred during the first few hundred years of the solar system. Possibly happened when the Jovian planets moved into their current orbits, sending asteroids and comets to the terrestrial planets.
How did the Moon form?
Possibly a giant impact from space sent Earth rock into spaced, and the resulting gas formed the Moon.
The Moon's composition is similar to Earth's outer layers.
The Moon contains smaller proportion of easily vaporized materials which would be vaporized when Earth was impacted.