Week 3: Origin of the Solar System

Question 1

Define “Molecular Clouds”

Answer 1

A type of interstellar clouds whose density and size allows molecules such as H2 to form.

Question 2

Give 3 properties of a pre-MS star

Answer 2

1) Central temperature too low for nuclear fusion
2) Low to intermediate mass
3) Emitted radiation comes entirely from gravitational contraction

Question 3

Give 5 requirements for a model describing solar system formation

Answer 3

1) All planets orbit in the same direction
2) The Sun rotates in the same direction
3) The Sun contains 99% of the total mass
4) Inner planets are terrestrial and rocky
5) Outer planets are gas giants

Question 4

State the 2 fundamental problems faced by most models and explain how the Solar Nebular theory addresses these problems

Answer 4

2 Fundamental problems:
1) The model must make a flat system with everything rotating and orbiting in the same direction
2) The model must grow a planet out of interstellar clouds with appropriate chemistry

The SNT addresses this as the combination of gravitational collapse and conservation of angular momentum is achieved via collapsing primordial clouds

Question 5

Describe the Solar Nebula Theory of Solar System formation

Answer 5

• Solar Nebular gravitationally contracts, heats up, flattens, and spins
• Dust grains condense, resulting in rocks/ metals in the inner system, and ice in the outer systems
• These accrete into planetesimals, then into protoplanets as accretion continues
• Protoplanets become planets, which then undergo differentiation to form layers
• Leftover materials form comets/ asteroids

Question 6

Name 2 ways in which planetesimals form, and 3 ways in which they grow

Answer 6

2 Theories of planetesimals formation:
1) Core accretion: Planets form by coagulating ice/ rock core and gravitationally capturing gas
2) Gravitational collapse: Planets form by self-gravity

3 Methods of planet growth:
1) Collisions of dust grains
2) Electrostatic binding
3) Gravitational attraction