Earth Under Threat From Dark Comets

An anonymous reader writes "Comets could be the most significant impact hazard to Earth, with sky surveys underestimating the number that are potentially devastating by a factor of between 10 and 100, UK astrophysicists say."

Comments

Re:Slashdotted

[morgan_greywolf]

Here we go, try this article from New Scientist, which has the same story.

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.

The article goes on to say that "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."

Re:Slashdotted

[dkf]

Organic != made by life. Means nonmetals, so Carbon, Nitrogen Sulfur and related compounds.

It specifically means Carbon. There's really quite a bit of it about in space, and the process of evaporating off all the ice from the comet will mean that that which is there has been thoroughly concentrated to make something rather like soot. Such materials, especially in ultra-low gravity environments (so preventing the collapse of complicated micro-strucutres), are incredibly black, making the comet harder to see than a black cat in a coal cellar. At night with no torch.

The New Scientist article goes on to mention that the best hope of spotting these things may be in the infra-red range, as they'll be absorbing all the sunlight that falls on them and reradiating it. Sounds tricky to me, but just might work...