Part 2: Solar System Formation

1
Part 2 Solar System Formation

• Our Milky Way Galaxy is filled with cold, dark
  clouds of gas and dust.
• These clouds are mostly hydrogen and helium with
  dust containing mostly iron, rock, and ice.
• The Solar System is thought to have formed from a
  huge, slowly rotating cloud about 4.5 billion
  years ago
• A nearby passing star or stellar explosion may
  have caused the cloud to collapse

2
Collapsing Gas Clouds

• As the cloud collapsed the original slow spin
  began to speed up. This caused the cloud to
  flatten into a disk shape.
• The gravitational pull of the cloud caused it to
  shrink further and caused most of the material to
  fall towards the core forming a large bulge.

3
Collapsing Gas Clouds?

• In the Great Nebula of the constellation Orion
  are huge clouds of gas and dust.
• Among these clouds the Hubble Space Telescope
  observed lumps and knots that appear to be new
  stars and planets being formed.

4
Planets in Formation?

• Around the star Beta Pictoris a large disk of
  dust and gas has been observed.
• The light from the star is much brighter than the
  disk so it had to be blocked for the disk to
  appear clearly.
• Disks have been seen around other stars too
  including Vega.

5
Birth of the Sun

• As material falls into towards the disk it
  collides with other material and heats up and
  melts.
• The increasing mass of the core also increases
  the gravitational pull and causes more material
  to be pulled in.
• When the mass is large enough and temperatures
  high enough nuclear fusion reactions begin in the
  core and a star is born!

6
Heating and Condensation of the Solar Nebula

• The heat from the Sun prevents ices from
  reforming on the dust grains in the region near
  the Sun.
• Ices condensed only in the outer parts of the
  Solar nebula.
• In the inner portion of the disk only materials
  like iron and silicates (rock) can condense into
  solids. Slowly they form clumps of material.
• In the outer portion of the disk much more
  material can condense as solids including ice.
  This extra material allows clumps to grow larger
  and faster.

7
Gravity does the job

• Within the disk, material is constantly colliding
  with one another. If the collisions are not too
  violent material may stick together.
• In the outer parts of the Solar Nebula the
  planets become large enough to have a significant
  gravitational pull and collect gas around them.
• Planets in the inner nebula can not grow enough
  to collect much gas.
• Eventually most but not all of the material was
  swept up by the planets.

8
The Last of the Planetesimals

• The remaining material exists today as
• comets which were flung out to a region far
  beyond Pluto called the Oort cloud and
• asteroids mostly between Mars and Jupiter (the
  Asteroid Belt) and beyond Pluto (the Kuiper Belt)