Comet

A comet is a ball of ice and rock that exists in space. When their orbit takes them close to a star, some of the ice melts and forms a tail behind it.

Halley's Comet was one of the best-known comets in Earth history. Its orbit brought it close to Earth approximately every seventy-five years. It collided with a Persopolisian ship in 1066. (AUDIO: The Time Capsule) The Cybermen time travelled to 1985, planning to divert Halley's Comet to crash into Earth, thus preventing the destruction of their home planet Mondas the following year. The plan was foiled by the Sixth Doctor. (TV: Attack of the Cybermen)

A comet was discovered by the astronomer Clancy in 1661. It returned to Earth every one hundred fifty-seven years. (AUDIO: The Ghosts of N-Space)

The Terileptil escape pod that crashed in England in 1666 was thought to be a comet. (TV: The Visitation)

In 250,339, the comet Schuler-Khan was on a collision course with the Gyre. (PROSE: Night of the Humans)