QUESTION:
Why can HST resolve nebulae that are thousands of light years away
but not Pluto, a planet in our own solar system?
 
ANSWER from  Meenakshi Sahu on April 29th,1996;
The answer is that the angular size of Pluto is smaller than that of
the Eagle Nebula (for example), even though Pluto is closer to us.
This is just as if you are looking at a small ant which is 6 feet away 
from you and a big tree 100 yards away from you. The ant is closer to 
you but you cannot see it very clearly because it is small, while you 
can see the tree and its leaves clearly although they are farther
away.

The most recent estimate of Pluto's diameter is about 1438 miles and
it is 3688 million miles away from the Sun. The Eagle nebula on the
other hand is roughly one light year across and about 7,000 light
years away. Our entire solar sytem would fit into one of the small
fuzzy objects seen on the recent HST images