Why are orbits of Comets unstable?

[Riccardo K]

Homework Statement

The orbits of the planets remains extremely stable over long times however this not always true for comets. Can you explain why not? What hazards might they encounter during their travels?

Homework Equations

None

The Attempt at a Solution

I think that due to the comet's not having a determined orbit while the comet is traveling it gets affected by multiple gravitational forces so its path is changed and it might crash into another object.

 

[gneill]

You'll have to expand a bit on what you mean by "comet's not having a determined orbit while the comet is traveling". The gravitational influence comment is correct, but could also use some additional fleshing out. For example, what is it about a comet that makes it susceptible to these gravitational influences whereas planets are relatively unaffected despite also constantly being subjected to multiple changing gravitational influences.

You might want to consider the various characteristics of a typical comet as compared to those of say, planets and asteroids (orbit energy, eccentricity, orientation). Are there things other than gravity that influence them? Do they change over different parts of the orbit?