Why do comets develop tails near the Sun?

Comets are icy bodies that spend most of their time far from the Sun in the cold outer solar system. When they approach the inner solar system, sunlight heats their surface and causes volatile materials to sublimate, or go directly from solid to gas. That escaping gas carries dust with it, creating a bright coma and often two tails: a dust tail and an ion tail. The ion tail points away from the Sun because charged particles are swept by the solar wind, not because the comet is moving backward.