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Space Science

Earth Under Threat From Dark Comets 149

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."
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Earth Under Threat From Dark Comets

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  • Re:Slashdotted (Score:5, Informative)

    by morgan_greywolf ( 835522 ) on Monday February 16, 2009 @11:49AM (#26872813) Homepage Journal

    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 (Score:3, Informative)

    by clang_jangle ( 975789 ) on Monday February 16, 2009 @11:52AM (#26872853) Journal
    Try this [] one instead.
  • Re:Seriously? WTF? (Score:5, Informative)

    by meringuoid ( 568297 ) on Monday February 16, 2009 @11:57AM (#26872939)
    Just what are the "other" impact hazards? I'm very curious about this.


    Asteroids orbit nearer the Sun, and many of them have paths that cross Earth's orbit quite frequently. They're a menace all right, but a menace that can be mapped and measured. Comets on the other hand have long, highly elliptical orbits that carry them far from the Sun. Though any given comet won't pass near the Earth anywhere near so often, they exist in colossal numbers, and for all we know one could come barrelling out of the dark to kill us all next month. We could in principle track every rock of dangerous size in the inner solar system. We haven't a prayer of tracking all the comets.

  • Re:Seriously? WTF? (Score:3, Informative)

    by mrsquid0 ( 1335303 ) on Monday February 16, 2009 @12:18PM (#26873225) Homepage

    >>"Comets could be the most significant impact hazard to Earth
    >Just what are the "other" impact hazards? I'm very curious about

    Asteroids are the other impact threat. There is also a small risk from man-made space junk. The biggest threat is comets because they tend to be moving far faster than asteroids typically do (near parabolic orbits vs low-eccentricity elliptical orbits), so the kinetic energy in a comet impact can be much higher than in an asteroid impact. Another problem with comets is that they can come at us from the direction of the Sun, so it can be very hard to detect them before the impact shockwave turns us to jelly.

  • Re:Slashdotted (Score:5, Informative)

    by dkf ( 304284 ) <> on Monday February 16, 2009 @12:18PM (#26873229) Homepage

    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...

  • Re:Launch Nukes (Score:2, Informative)

    by navyjeff ( 900138 ) on Monday February 16, 2009 @12:26PM (#26873319) Homepage Journal
  • Re:No torch? (Score:3, Informative)

    by morgan_greywolf ( 835522 ) on Monday February 16, 2009 @02:17PM (#26874851) Homepage Journal

    Monty Python? Benny Hill? Blackadder? Douglas Adams? Rowan Atkinson?

    Subtle innuendo has long been a staple of British humour.

  • Re:Silly article (Score:3, Informative)

    by nyctopterus ( 717502 ) on Monday February 16, 2009 @03:20PM (#26875699) Homepage

    Actually, impacts the size of the Yucatan K/T event are global in scope, and do not occur on average every 60 million years. Even if every major extinction event was caused by a an impact (which is highly doubtful), they are much more widely spaced than a sixty million year average.

    Maybe what we're looking at is something more like the Younger Dryas impact event [] hit every 60 million year on average. Which, though unlikely, would of course be a major fricken disaster for humanity if it happened within our lifetimes.

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