Nebular Hypothesis

Question 1

What did the solar system form from

Answer 1

solar nebula

Question 2

what was the solar nebula

Answer 2

-a very cold cloud of gas
- slight amount of rotation
~ 2-3 solar masses, 100 AU in diameter
- 75% H, 23% He, 2% else (like stars)

Question 3

Where did the solar nebula come from

Answer 3

it was a tiny part of the interstellar medium (ISM), distribution of gas, ice and dust in the Milky Way

Question 4

Where did the ISM come from?

Answer 4

The big bang - gave us hydrogen and helium for gas and ices

Exploding stars - gave us all other elements for dust, gas and ices

Question 5

1st part of nebular hypothesis:

Answer 5

gravity collapsed the solar nebula into 2 parts
- central concentration (sun)
- disk
as it shrank it rotated faster and faster bc of conservation of angular momentum

Question 6

How did the different planet types come from the solar nebula?

Answer 6

The central concentration, protosun, became very hot and vaporized inner ice and their atoms were pushed by light beyond 4 AU
- this formed the less dense, more massive Jovian planets
The dust grains didn’t vaporize and migrate; they remained within 4 AU
- this formed the rockier terrestrial planets

Question 7

What happened in the accretion stage?

Answer 7

The gas and dust swept around the protosun, they collided and merged
- first chondrites: the first rock-sized bodies that formed from
dust grains
- then planetesimals (chemically diff.)
- then protoplanets
- then planets

as the disk collapsed and merged 1-2 solar masses were ejected

Question 8

Oddities in searching for more solar nebulas:

Answer 8

• planets found so far seem to be large, close to the star, and elliptical which is unlike our system
• could be bc observational bias