Comet"s Tail

Seems to me comets tails can tell us a lot about our solar system. We
know the EM energy of the sun can move these tails. The tails must have
the density of a vapor,such as steam. Much of this vapor has to be lost
to space. The solid body of the comet could be dry ice,and ammonia
continually giving added vapor to the tail. Seems the faster the comet
is moving the longer the tail??? What comet holds the speed record? Is
Haley the largest comet? Can the Hubble see a comet that is at a
distance as far out as Jupiter? Do comets spin? Do comets get
noticeably smaller? Bert