riddlemethis

I have some rather uneducated simple questions about comets. First - are all comets made of the same things, and if not what are the possible compositions? Second - are the nuclei of all comets made of the same thing, and if not what are the possible compositions? Third - what thing (other than direct impacts) can affect the orbit or path of a comet? Fourth - do comets have a magnetic component? Fifth - in regard to rotation, why do some comets spin asymmetrically while others spin symmetrically. What would cause the difference? Would it be the composition or shape nuclei of the comet or something else? Sixth - what if any effect would a comet have on the sun in a close approach and why? Seventh - what effect could the sun have on a close approaching comet and would it's composition change this answer in any way? Eight - When comets approach the sun is their decomposition symmetrical or asymmetrical. If asymmetrical can asymmetrical degassing cause a change in trajectory? If not, why not? Ninth - how and why are comet trajectories changed (for example by NASA) - is it simply observational? Are there historical examples of comets approaching the sun and then breaking apart? Could a comet that broke apart near the sun survive the break-up or would the sun's gravity envelop the parts? Thanks!