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fosborn
2011-Jun-05, 02:34 PM
Why does the Oort cloud not evolve into an Oort disk? Is it just left over debris that remains in the same galactic orbit as the solar system and the sun's gravity has little, local effect?

antoniseb
2011-Jun-05, 02:39 PM
We believe it is not a disk because the inclination of long period comet orbits is nearly random.
AFAIK, it is thought to be not a disk because the members were ejected from the inner solar system by interactions with the giant planets that would send the objects in directions related to the direction of approach to the planet, too microscopic to be based on the ecliptic.

fosborn
2011-Jun-05, 03:11 PM
Thanks, if I had looked all the way down my search list, I would have found your explanation in a similar discussion. Sorry to be redundant.
http://www.bautforum.com/showthread.php/102565-What-exactly-is-holding-the-Oort-Cloud-intact

HypersonicMan
2011-Jun-05, 07:36 PM
The Oort cloud may have started out more disk-like (although it depends on how it got formed in the first place). The tidal forces caused by the galaxy torque the orbits of Oort cloud objects so that their orbits are isotropic, rather than confined to near the ecliptic plane. So even if it had started out as a disk, the Oort cloud is so distant that the galaxy will scramble its orbits into a cloud.

Amber Robot
2011-Jun-06, 12:17 AM
Why does the Oort cloud not evolve into an Oort disk? Is it just left over debris that remains in the same galactic orbit as the solar system and the sun's gravity has little, local effect?

I think it's more about the density of objects in the Oort cloud. For a cloud to settle to a disk you need some way of changing the energy/angular momentum of the system. In a protoplanetary gas/dust disk the densities are quite high (as things in space go) but the objects in the Oort cloud are not significantly interacting with each other.

HypersonicMan
2011-Jun-06, 01:27 AM
Oort cloud comets, like all objects in the solar system, probably had to form from a protoplanetary disk. Therefore, some mechanism must be invoked to explain their current orbits. Galactic tides is the currently favored one, although a recently proposed mechanism for forming the Oort cloud from the "swapping" of comets ejected by the Sun's siblings within its birth cluster does not require it: http://www.swri.org/9what/releases/2010/cometorigins.htm Nevertheless, no matter how you get Oort cloud comets out to their distant orbits, they are so loosely bound to the Sun that galactic tides will torque them no matter what.

fosborn
2011-Jun-06, 01:47 AM
Thanks for the input.

I think I like the idea of the solar system ejecting material. It seems the simplest. There's no trying to figure how it is maintained, how to stabilize orbits in a cloud. What doesn't escape eventually returns. I wonder if this is even compatible with some paper I saw on magnetic breaking or torque in star formation. Could such a process be involved in ejecting material also ( if this is wondering to far off topic, please ignore)?

Thanks
Frank

HypersonicMan
2011-Jun-06, 01:53 AM
Jupiter is likely the primary agent responsible for the ejection. Magnetic breaking cause a star (including the Sun) to slow its spin, and probably has nothing to do with the Oort cloud.

fosborn
2011-Jun-06, 02:38 AM
Ok, thanks for the reply.