What is the Difference between a Comet and an Asteroid?
There are several important differences between comets and asteroids, though the distinction between the two is not absolute. The primary difference is that comets have a tail, whereas asteroids do not. Also important is that comets tend to have extremely elongated orbits, sometimes traveling as far as 50,000 AU (astronomical units, or Earth-Sun distances) or farther away from the Sun, though short-period comets only travel as far as the outer planets before returning to the inner solar system. Asteroids tend to have more circular orbits, and coalesce in belts, like the asteroid belt between Mars and Jupiter or the Kuiper belt beyond the orbit of Neptune. The tail and coma (atmosphere) of comets is generated by solar heating which vaporizes volatiles (substances with a low boiling point) on a comet’s surface, especially ice, and causes it to be ejected all around the comet. Then, the solar wind carries away the vaporized materials, forming the tail. Though one may imagine that the tail
• A comet is a small Solar System body that orbits the Sun and, when close enough to the Sun, exhibits a visible coma (atmosphere) or a tail — both primarily from the effects of solar radiation upon the comet’s nucleus. Comet nuclei are themselves loose collections of ice, dust and small rocky particles, measuring a few kilometres or tens of kilometres across.
