A comet may possess several dust tails in addition to a gas tail. The antitail is actually a very thin layer of dust lying along the orbit of the comet, having been expelled at an earlier stage. Many comets, especially short-period ones, slowly disintegrate, mainly under the influence of the Sun's gravitational force. Recently, several collisions of comets with the Sun have been observed with coronographs aboard satellites. A regular decrease in the brightness of short-period comets is often observed.
Comets also leave waste products behind in their orbits, in the form of millions of meteoroids.
Also, the impact of a comet, or piece of a comet, remains one of the more plausible explanations for a tremendous blast that occurred in the Tunguska region of Russia in June 1908. Various theories have been developed in recent centuries to account for comets, but the one most widely accepted at present is that comets were formed at the same time as the rest of the solar system. Both proposals have been widely accepted, with some astronomers suggesting that the Oort and Kuiper clouds actually merge along the Oort cloud's much denser inner boundary. Perturbations by interstellar clouds or passing stars would cause some of the comet materials to dislodge and enter the inner solar system in the form of comets, with short-period comets more likely arising from the Kuiper belt.