The Formation of the Solar System

The Nebular Hypothesis The Solar System formed ~ 4.6 billion years ago Evidence from:  meteorites ( billion years old)  moon rocks (~4.0 billion years old)  Earth Rocks(~3.9 billion years old) sedimentary minerals ~ 4.2 by

The Beginning All stars, including our sun come from nebulae Nebulae are the remains of old stars that have exploded Nebulae contain all of the natural elements Eggs in nebula are where stars are born

The Big Spin - An external force causes the “egg” to spin counterclockwise The gas cloud initially rotated slowly Gravity pulls the cloud inward Conservation of Angular Momentum As the cloud begins to shrink, it spins faster Think of a ice skater Quickly rotating objects become flattened.

The contraction of the solar nebula made it spin faster and heat up. (Compressed gas gets hotter.) Temperature of solar nebula: > 2000 Kelvin near Sun; < 50 Kelvin far from Sun.

The Disc Over 90% of the material was in the center Less than 10% of the material was in the disc surrounding it SUN Planets, comets, Asteroids, Moons

The Formation of the Planets Accretion: particles in the disc condensed forming ice and rock these particles continued to collide and combine into large planetesimals Continuing to spin, compress and collide the planets and moons formed

Accretion of Planetesimals Many smaller objects collected into just a few large ones

Inside the frost line: Too hot for hydrogen compounds to form ices. Outside the frost line: Cold enough for ices to form. Fig 9.5 Why two types of planets?

The Formation of the Sun Within the center of the disc: Compression and Friction Temperature Increase Sun “turned on” Hydrogen fusion began

The Solar Wind blew excess gas toward the outer planets leaving the inner planets rocky ending the period of planet formation

What makes this a good hypothesis? All of the planets travel in the same direction (counterclockwise) All of the planets are in the same plane Angular Momentum is clearly understood Nebula are very real and very common

How do we explain “exceptions to the rules”?

Heavy Bombardment Leftover planetesimals bombarded other objects in the late stages of solar system formation

Odd Rotation Giant impacts might explain the different rotation axes of some planets

Origin of Earth’s Water Water may have come to Earth by way of icy planetesimals from outer solar system

Captured Moons Unusual moons of some planets may be captured planetesimals

How do we explain the existence of Earth’s moon?

Giant Impact Hypothesis

Giant Impact Giant impact stripped matter from Earth’s crust Stripped matter began to orbit Then accreted into Moon

Was our solar system destined to be? Formation of planets in the solar nebula seems inevitable But details of individual planets could have been different