PV Gap

Mae Said:

How I can possibly identify different planetary bodies?

We Answered:

Asteroids and small moons are small and irregularly shaped. Larger bodies are round, or nearly round. Large Moons and planets can be distinguished by their atmospheres (if they have one) or by colours and distinctive land forms (if they don't). Comets have long tails when near the Sun, but look like asteroids when far from the Sun or seen close up.

Some distinguishing characteristics:
Saturn: rings
Jupiter: well developed cloud belts, Great Red Spot.
Uranus and Neptune: blue-green colour)
Mars: peach colour with polar cap(s) and darker makings
Venus: featureless white clouds
Earth: blue oceans, white clouds, polar caps

The tough ones to distinguish are the Moon, Mercury, and the many larger moons of Jupiter, Saturn, Uranus, and Neptune. These nearly all look the same, but some have more craters than others, and some have distinguishing large craters. The only ones that are really different are Io (reddish, many active volcanoes), Europa (ice surface) and Titan (dense atmosphere with methane lakes underneath).