solar system formation

Question 1

what does any origin theory need to explain

Answer 1

1. most of the solar systems mass is in the sun
2. most of the angular momentum is in the planets
3. orbital plane and direction of the planets are roughly the same
4. the sun rotates in the same direction as the orbits
5. the size and composition of the planets

Question 2

What’s the nebular hypothesis

Answer 2

1. starts with collapsing/rotating interstellar gas
2. densest at the centre where the sun forms
3. remaining material forms a thin disk
4. small grains condense
5. gravity causes clumping into proto-planets
6. Volatiles driven out by solar wind to the start of fusion in the sun
7. planets grow by sweeping up the remaining dust
8. Gravity causes some small planets to collide

Question 3

what’s the Jean mass

Answer 3

the minimum mass for a interstellar gas cloud to collapse under its own weight

Question 4

what’s the collapsing timescale

Answer 4

aka the free fall time scale, (t subscript ff ).
The time taken for the cloud to become strongly centrally condensed

Question 5

derive the collapsing timescale

Answer 5

the time scale is related to the gravitational constant G.
G is measured in m³ s⁻² kg⁻¹

Use dimensional analysis to get t = sqrt(1/Gρ)
where ρ is the density of the gas cloud

Question 6

how does the disc form in the nebular hypothesis

Answer 6

The gas cloud is rotating, the angular momentum slows this collapse perpendicular to the rotation axis. this results in a flat disc.

use L= mvr where v = sqrt(GM/r) and rearrange for r
this results in an equation where r is proportional to L/m squared.

Question 7

how do you find the distance from a star at which a given element can be solid

Answer 7

The condensation temperature will be given (the temp at which an element solidifies)

use the equilibrium temperature equation (the one that uses the albedo) and rearrange for the distance, d

Question 8

what’s planet migration

Answer 8

early planets that formed had a frictional interaction with the disc of gas/dust. This reduced it angular momentum and caused in to spiral into the sun

Question 9

what caused the debris in the solar system

Answer 9

Debris is in regions where planet formation failed

Trans-Neptunian object:
Too far out so the disc was too low-density to form planets

Asteroid belt:
Orbital resonance with Jupiter disrupted planet growth

Question 10

what’s the snowline

Answer 10

the distance from the sun at which water/methane and ammonia are solid. this is at 200K temperature which gives ~2AU