‘Dark’ Comets May Pose Threat to Earth

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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 University and David Asher at Armagh Observatory in Northern Ireland claim that many comets could be going undetected. “There is a case to be made that dark, dormant comets are a significant but largely unseen hazard,” says Napier.

In previous work, Napier and Janaki Wickramasinghe, also at Cardiff, have suggested that when the solar system periodically passes through the galactic plane, it nudges comets in our direction (New Scientist, 19 April 2008, p 10).

These periodic comet showers appear to correlate with the dates of ancient impact craters found on Earth, which would suggest that most impactors in the past were comets, not asteroids.

[link to spaceguardcentre.com (secure)]