Once hoped to be the most spectacular comet in a generation, Horizon examines the insights Comet ISON might bring to some of science's greatest mysteries.

It was hoped that Comet ISON could be the brightest and most spectacular comet for a generation. After travelling towards the sun for ten thousand years, it appeared to have been disintegrated by the heat and tidal forces of the sun in early December 2013.

But ISON's tail of vapourised gas and water, hundreds of millions of kilometres long, may give insights into some of the greatest mysteries of science. It could help explain the origins of the solar system, whether earth's water was delivered on comets and even whether we are alone in the universe.