Comet
In short
An icy small Solar System body that releases gas and dust when it passes close to the Sun.
In plain words
Comets are like dirty snowballs flying through space. As they get near the Sun, the heat turns their ice into gas, creating a glowing cloud and a long tail.
A simple example
When a comet enters the inner solar system, it develops a bright coma and a tail that points away from the Sun.
Why it matters
Studying comets helps scientists understand how the early solar system formed. They carry ancient ice and organic materials from the furthest reaches of space.
Easy to mix up
Do not confuse a comet with an asteroid, which is mostly made of rock and metal rather than ice.