Unseen “dark” comets could pose a deadly threat to Earth. Citing recent warnings from astronomers, The Daily Telegraph says there should be around 3,000 comets in the solar system, but only 25 have been identified so far. Many comets are simply going unnoticed.
A dark comet is a comet that reflects less light due to the water on its surface having evaporated, which can make it nearly impossible to detect.
New Scientist Magazine reports:
“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.”
Napier has been especially vocal on this issue. "There is a case to be made that dark, dormant comets are a significant but largely unseen hazard," he said in a statement to the Telegraph.
The Telegraph also reports that in the past, astronomers have spotted comets heading toward Earth just days before they passed. According to the article:
“In 1983 a comet called IRAS-Araki-Alcock passed at a distance of just 5 million kilometres, the closest of any comet for 200 years, but it was noticed just a fortnight beforehand.”
Not everyone is expressing the same level of concern, however. In a statement to New Scientist, Clark Chapman from the Southwest Research Institute in Boulder, Colorado, said that dark comets "would absorb sunlight very well" and so could be detected by the heat they emit.
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