Dark comets may be on collision course with Earth

The Daily Mail newspaper, on the 12th of February 2009, has an article about comets that can not been seen and could collide with Earth without warning.

Thousands of invisible 'dark' comets may be posing an unseen threat to Earth, according to two British astronomers.

Professor Bill Napier, from the University of Cardiff, told New Scientist magazine: 'There is a case to be made that dark, dormant comets are a significant but largely unseen hazard.'

The rate that bright comets pass through the Solar System suggests there should be 3,000 of them flying around, yet only 25 have been detected. Most may have remained hidden because they are too dark to see, say the astronomers.