Comets are best seen after midnight. Comets orbit the Sun in nearly circular orbits. Thus, you would want to study objects that had undergone the least amount of chemical change. The asteroid orbits are confined to the ecliptic. The average asteroid diameter is only a few kilometers in size.
Some asteroids are reddish while others are dark.
The total amount of mass in the asteroid belt is small compared to a planet. The asteroids are gaseous while the planets are rocky. The effect of the cloud s gravity on the orbit of Neptune. The detection of faint objects in the comet cloud by sensitive telescopes. The fact that nearby stars perturb objects in the cloud into orbits that pass near the Sun.