Why do comets develop tails when they get close to the Sun?

Comets are icy bodies that spend most of their time far from the Sun, where they stay frozen. As they approach the inner Solar System, sunlight warms their surface and causes ices to sublimate directly into gas. That gas carries dust away from the nucleus, forming a glowing coma and one or two tails. The dust tail is pushed by sunlight, while the ion tail is shaped by the solar wind and points away from the Sun. This process explains why comets can look dramatically different depending on how close they are to the Sun.