According to a report in New Scientist, UK-based astronomers Bill Napier at Cardiff University and David Asher at Armagh Observatory in Northern Ireland have made the claim that many such comets could be going undetected.
"There is a case to be made that dark, dormant comets are a significant but largely unseen hazard," said 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.
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.
Now, Napier and Asher warn that some of these comets may still be zipping around the solar system. Other observations support their case.
The rate that bright comets enter the solar system implies there should be around 3000 of them buzzing around, and yet only 25 are known.
According to the astronomers, we may not see them, simply because they are too dark.
Such dark comets are not unheard of. They occur when an "active" comet's reflective water ice has evaporated away, leaving behind an organic crust that only reflects a small fraction of light.
Clark Chapman at the Southwest Research Institute in Boulder, Colorado, said that such dark comets "would absorb sunlight very well" and so could be detected by the heat they would emit. (ANI)