A composite of images from NASA’s Deep Space 1 spacecraft shows features of comet Borrelly’s nucleus, dust jets escaping the nucleus and the cloud-like “coma” of dust and gases surrounding the nucleus. False colour is used to reveal details of the jets and coma (Image: JPL / NASA)

SWATHES of dark comets may be prowling the solar system, posing a deadly threat to Earth.

Hazardous comets and asteroids are monitored by various space agencies under an umbrella effort known as Spaceguard. The vast majority of objects found so far are rocky asteroids. Yet UK-based astronomers Bill Napier at Cardiff …