Encke's comet. Optical telescope views of the movement of Encke's comet (in crosshairs) against the background stars. Encke's comet (2P/Encke) has the shortest orbital period of any known comet, orbiting the Sun in just 3.3 years. A comet is a chunk of ices and dust that orbits the Sun in an elliptical orbit. As it nears the Sun, the heat causes some of the ice to boil off into space, creating a cloud of gas (coma) around the comet. A long tail of gas and dust particles is blown away from the comet by the pressure of sunlight. These images were taken at 10:33 (left) and 10:53 (right) on the morning of 26th October 2003, when Encke was near Earth.