QUESTION:
How do comets go so fast in space?  Do they have some kind of force 
pushing them?  I think there are little bits of gasses pushing the comet 
and that is what makes it go so fast.

ANSWER from Dave Hollenbach on May 20:
The comets move fast because of the gravity of the sun, which pulls
them to faster and faster speed as they fall closer to the sun.  The
gases which do come off the comets don't push them like a rocket to
high speed.  In fact, the sunlight shining on the icy comet causes
more gases to come off the "front", which slightly slows them down.
The wind from the sun then pushes these gases into the big long
tail of the comet, which always points away from the sun.

Did you know that the Earth has to move 20 miles per second in
order not to fall into the sun?  So we are moving pretty fast too!
The sun has a lot of gravity because it has a million times as
much mass as the Earth.