Formation of the Solar System
What We Know
Physical Properties of the Planets
INNER PLANETS
• Close to Sun
• Close to each other
• Small size
• Solid and Rocky
• Higher Density
OUTER PLANETS
• Far from Sun
• Spread far apart
• Large size
• Gaseous
• Lower Density
Orbital Properties of the Planets
• All orbit the sun counterclockwise
• All spin on their axis counterclockwise
– Exception = Venus spins upside down
• All orbit in nearly the same plane
• All orbits are nearly circular
• All meteorites are 4.6 billion years old
Formation of the Solar System
How do we tie together the information we
have about the planets with the physical
laws of nature to write a story about the
formation of the solar system?
Video clip – Origins: Earth is Born
What makes up the solar system?
A. Sun = 99% of the matter in the solar
system
B. 8 planets, satellites (moons), asteroids,
and comets
C. The Oort Cloud extends far beyond
orbit of Pluto – as far ras 150,000 AU
Origins of the solar system
A. Formed about 4.6 billion years ago
B. Formed in a Solar Nebula from a
supernova explosion
C. Evidence = presence of heavy
elements
Solar Nebula Model of Solar System Formation
A cloud of gas and dust, the Solar Nebula, is
disturbed by a shock wave and begins to
collapse.
1. Gas and dust is compressed and begins to
be pulled inward by Gravity.
2. Most of the matter is pulled into a central
area where the pressure increases and the
matter begins to heat up.
3. The matter begins to spin faster as it
collapses.
4. A Protosun is formed, composed of nearly all
(99%) of the matter in the rotating system.
Formation of the Planets
5. The leftover debris flattens into a swirling disk of
gas and dust particles.
6. Particles of gas and dust in the rotating disk collide
and begin to stick together.
7. Colliding particles grow into small planetesimals
whose gravity draws in more particles, forming
protoplanets (This process is called accretion).
8. Nuclear fusion in the core ignites the star.
9. Hydrogen and helium gases are swept out of the
inner solar system by a wave of solar emissions.
10. The young planets continue to be bombarded by
debris left in the rotating disk, creating heavily
cratered surfaces.