<p>Reading about the formation of planetary disks, one of the major problems, it seems like, is the evacuation of angular momentum. Aparently planets can't form with the amount o angular momentum the system has in its early stages. I think I understand where that excess comes from, the collapse of the nebula onto itself and provoking a spin. Then there are many hypothesis on how it's evacuated, which are mostly pretty logical.</p>

<p>Now my question, as a beginner in the study of physics, is this: Why does the angular momentum even need to be evacuated? If the angular momentum is too big, why can't planets still form? Does this have something to do with too much kinetic energy in the system?
Thank you!</p>

CC BY-SA 3.0
2016-12-29T13:35:58.500Z
And a good answer on Physics SE too.
ProfRob
CC BY-SA 3.0
2018-02-21T16:52:19.923Z
@Warrick Please convert to an answer.
called2voyage
CC BY-SA 3.0
2015-03-08T10:50:10.037Z
I suppose this is related with the formation of the system itself (the mass has to flow towards the inner region). Could you please link a reference where you read about the angular momentum condition?
Py-ser
CC BY-SA 3.0
2015-03-08T10:54:29.230Z
I have several sources, some of which come from a francophone library, I don't know whether it will be of any help. About the evacuation, I am mostly basing myself on this video: 
https://www.youtube.com/watch?v=tEgw0PXwkGE
L.R.
CC BY-SA 3.0
2015-03-11T07:10:07.937Z
Hmmm... I'm not expert on planet formation, but a basic issue will be accumulating enough material to make a planet in the first place. For a specified amount of angular momentum, material must orbit at a certain distance from the central object. So, at first, too much material is too far away, and to get closer it has to lose angular momentum.
Warrick
CC BY-SA 3.0
2015-03-11T22:16:36.827Z
[Also on Physics.](https://physics.stackexchange.com/questions/169545/angular-momentum-in-planetary-disk-formation)
HDE 226868
<solar-system><astrophysics><accretion-discs>
Angular momentum in planetary disk formation
L.R.
# Angular momentum in planetary disk formation

(Asked by: username_0 on 2015-03-08)

Reading about the formation of planetary disks, one of the major problems, it seems like, is the evacuation of angular momentum. Aparently planets can't form with the amount o angular momentum the system has in its early stages. I think I understand where that excess comes from, the collapse of the nebula onto itself and provoking a spin. Then there are many hypothesis on how it's evacuated, which are mostly pretty logical.

Now my question, as a beginner in the study of physics, is this: Why does the angular momentum even need to be evacuated? If the angular momentum is too big, why can't planets still form? Does this have something to do with too much kinetic energy in the system?
Thank you!

**Tags:** solar-system, astrophysics, accretion-discs

> **Comments:**
> **username_3**: I suppose this is related with the formation of the system itself (the mass has to flow towards the inner region). Could you please link a reference where you read about the angular momentum condition?  
> **username_0**: I have several sources, some of which come from a francophone library, I don't know whether it will be of any help. About the evacuation, I am mostly basing myself on this video:  https://www.youtube.com/watch?v=tEgw0PXwkGE  
> **username_4**: Hmmm... I'm not expert on planet formation, but a basic issue will be accumulating enough material to make a planet in the first place. For a specified amount of angular momentum, material must orbit at a certain distance from the central object. So, at first, too much material is too far away, and to get closer it has to lose angular momentum.  
> **username_5**: [Also on Physics.](https://physics.stackexchange.com/questions/169545/angular-momentum-in-planetary-disk-formation)  
> **username_1**: And a good answer on Physics SE too.  
> **username_2**: @username_4 Please convert to an answer.  

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