Why Is the Velocity of an Oort Cloud Object Approximately Zero?

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Discussion Overview

The discussion centers on the velocity of objects in the Oort Cloud, particularly why it is considered to be approximately zero. Participants explore the implications of potential and kinetic energy in this context, as well as the concept of orbital mechanics at great distances from the Sun.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that the energy of an Oort cloud object is approximately zero, with potential and kinetic energy balancing out, and questions why the velocity is also considered approximately zero.
  • Another participant suggests that the reference to velocity might pertain to radial velocity with respect to Earth, which could be very small.
  • A participant cites their lecture notes indicating that the velocity of an Oort cloud object is approximately zero due to stable orbits at large distances.
  • One reply challenges the completeness of the original notes and emphasizes the need for clarification from the lecturer regarding the context of velocity.
  • Another participant proposes that the velocity in question refers to the linear velocity of an object in orbit at a specific moment.
  • A later contribution states that at great distances, such as in the Oort Cloud, an object requires minimal velocity to maintain its orbit, reiterating the use of the term 'approximately'.
  • It is mentioned that calculations using Newton's or Kepler's laws could provide insights into how close to zero the velocity is for an object in a circular orbit at a distance of one light-year from the Sun.

Areas of Agreement / Disagreement

Participants express varying interpretations of the concept of velocity in the context of Oort cloud objects, with no consensus reached on the specifics of the velocity being discussed or its implications.

Contextual Notes

There are limitations in the discussion due to incomplete notes and the ambiguity surrounding the context of velocity (radial vs. linear) as well as the assumptions made about energy and distance.

I_laff
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I read that the the energy of an Oort cloud object is approximately zero, as in the potential energy plus the kinetic energy is equal to zero. I was also told that the radius was approximately infinite and the velocity is approximately zero. I understand why the radius is said to be infinite (since it is so far away from the Earth, it's radius from the itself to the Earth is treated as infinite).

However, what I do not understand is why the velocity of the Oort cloud object is zero. Any help on understanding why this is the case?
 
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Could you post a link to the article that you're referring to?

It sounds like they may have been referring to the radial velocity w.r.t. the earth. That would be pretty small.
 
It's just something from my lecture notes. Here is the extract, 'There are lots of debris left over from the formation of the Solar System, some of which forms the Oort cloud in the very outer Solar System. What is the typical energy of an Oort cloud object? The energy (E) is approximately 0 as the orbit is stable and v is approximately 0, r is approximately inf.'
 
I think that your notes are incomplete. It's going to be difficult for anyone to help you decipher what you wrote during a lecture. Was the lecturer referring to radial velocity or speaking of velocity in some other context? Similar logic for the other questions. Only you and the lecturer can say for sure. I would take your notes to him and see if he can help you with what you missed.
 
I believe the velocity that is being referred to is the linear velocity of a particle in orbit (i.e. the velocity at one moment of time during the orbit).

Orite, thanks for the help anyways :smile:
 
In the same way as the distance is approximately infinite, the orbital velocity is also approximately zero. At that distance an object needs hardly any velocity to stay in orbit.
The key word is 'approximately', of course.

Should be easy to calculate either from Newton's or Kepler's laws how close to 0 it is for an object in a circular orbit at, say, 1 ly from the Sun.
 

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