QUESTION:
Why does the Orbiter have to stay up there for 2 years?

ANSWER from Charlie Sobeck on February 7, 1996:
The Galileo Orbiter's primary mission will keep it in orbit around Jupiter for
2 years so it can get a long term view of the planet.  We have already sent 4
different spacecraft passed Jupiter (Pioneer 1 and 11, and Voyagers 1 and 2). 
But each of these spacecraft simply flew on past the planet, so we could only
observe Jupiter for brief periods of time.  On the other hand, Galileo will
stay around for at least 2 years so we can take a longer look at the planet.

Imagine that you wanted to learn more about a new park.  You would learn a lot
more if you spent some time walking around the park, playing on the swings and
such, as compared to simply looking at it through the car window as you drove
by!

In fact, the Galileo Orbiter will probably spend even more than 2 years (2
years is viewed as the minimum).  As long as it keeps working, it will stay
around Jupiter, learning more about the planet.  For example, Jupiter takes 12
years to go around the sun.  How long should the Orbiter stay in orbit in
order to see if Jupiter has seasons?