QUESTION: 
Why are the larger planets outside the asteroid belt and the small planets
close to the sun?  Are the large planets solid or gas?



ANSWER from Anne Sprague on November 9, 1995:
The gas-giants are gaseous in the outer layers and solids in the
deep interior.

The inner planets are small and rocky because they lost all their
gaseous hydrogen and helium.

Dr. A. Sprague


ANSWER from Tom McMahon on November 11, 1995:
Shortly after our sun turned into a star, the solar winds and solar 
radiation is thought to have evaporated or pushed the lighter materials 
(gases, water, and other ices) into the outer solar system. This left 
heavier materials to collect and condensed into the inner planets 
(Mercury, Venus, Earth Mars and the asteroids). The light material 
further out condensed into the gaseous planets (Jupiter, Saturn, Neptune 
and Uranus). These gas giants do not have any solid surface like the 
inner planets.

The material that the satllites of the outer planets are made of were 
trapped by gravity to the gaseous planets. The leftover ices and gas also 
formed the comets. There is thought to be a halo of comets far outside 
the orbit of Pluto.

Now Pluto is an enigma. Pluto is a big rock. Why is it out with the 
gaseous planets? No one really knows. Some scientist believe that Pluto 
was wandering around the solar system, after having been bumped out of 
orbit somewhere, and fell into its present orbit.

__________________________________________________________
Tom McMahon
University of Chicago
Yerkes Observatory