Thus, relatively massive dust tails are accelerated slowly and tend to be curved. The ion tails is much less massive, and is accelerated so greatly that it appears as a nearly straight line extending away from the comet opposite the Sun. Therefore, each time a comet visits the Sun, it loses some of its volatiles. Eventually, it becomes just another rocky mass in the solar system. Many scientists believe that some asteroids are extinct comet nuclei, comet that have lost all of their volatiles.
Most comets travel around the Sun in elliptical paths.
The time it takes a comet to make a complete orbit is called its period. Some comets have short periods of less than seven years. Others travel in such huge orbits that they pass near the Sun only once in thousands or even millions of years. No comets seem to have approached the Sun from beyond the limits of the solar system. Therefore, all comets seen by astronomers are considered part of the solar system.