Formation of the Solar SystemQ of D: How did the solar system form?

Formation of Solar System

Current theory is called accretion (a process of coming together) or Nebular Theory.

Accretion Ia.k.a “Solar Nebular Theory”

1. Start with a nebula – a cloud of dust and gas.

Accretion II

2. A shock wave causes gas and dust and start to condense – come together to form small rocks.

3. Gravity takes over (!) Pieces begin to clump into bigger and bigger pieces.

Accretion III3. It begins to spin as it condenses, and the

group of rocks, dust and planetesimals takes a flat disk shape.

4. Clumping pieces become planetesimals, which become protoplanets, which become planets and moons.

Accretion IV

5. The big clump in center is “protosun”. As it gets bigger, it gets hotter and denser.

6. When it becomes big enough, it ignites (nuclear fusion).

Accretion IV

7. Solar wind (from the sun) blows off remaining dust and debris.

• Inner planets are rocky and have metals. Heavy elements withstand the solar wind (gravity, again).

• Outer planets are made of light elements, H and He.

Other Facts

• We know from radioactive dating, the oldest rocks (on earth, moon, and mars) are approx. 4.6 billion years old. That’s the generally accepted age of the solar system.

• Over 150 planets have been identified on other stars.

• This is a “theory”. It ties together all of the available evidence, and it seems reasonable. We think it’s right, but……..

Evidence that supports the theory:

• Over 150 planets have been identified on other stars.• What we believe to be accretion disks have been observed.• Materials from Moon, Mars, meteorites appear to be of similar

ages and composition• Composition of the planets (inner and outer)• Motion of planets and sun• Law of gravity • Existence of solar wind• Asteroids – a broken or unformed planet?• What appear to be accretion disks have been observed around

protostars (Hubble photos of the Horsehead nebula)• We are always learning more.

Kuiper Belt

• A collection of icy planetesimals in orbit from Neptune to 100 AU or more.

Oort CloudThe Oort Cloud was discovered in 1950 by Dutch Astronomer Jan Oort.  It lies beyond the Kuiper belt some 30,000 AU to 1 Light Year away from the Sun.  The Oort Cloud is thought to be the origin of many of our long term comets.  The short term comets originate closer to home, in the Kuiper Belt, which lies just beyond the orbit of Neptune.

The distance from the sun to the earth is 1 astronomical unit (1AU).

Where does the Solar System end?