[meteorite-list] Comet Put on List of Potential Earth Impactors

[Sterling K. Webb]

Hi,

    Of course, I'll be long dead and my children will be (probably) be dead,
by 2085, and everybody I know and everybody you know, but it's time to take
life seriously, boys and girls, time to go put transponders on the 10 most
likely objects so we can track them all the time, time to spend some (more)
actual cash money on the search programs, dear Congressional idiots, time to
grow up as a species, stop scratching your rump and picking fleas off the
other monkeys and pay attention to the funny lights in the sky and the scary
ones, especially.
    The dinosaurs didn't and look what it got them.

Sterling K. Webb
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Ron Baalke wrote:

> http://www.newscientistspace.com/article/dn7449.html
>
> Comet put on list of potential Earth impactors
> David L Chandler
> New Scientist
> June 1, 2005
>
> A comet has been added to the list of potentially threatening near-Earth
> objects maintained by NASA's Jet Propulsion Laboratory. Comet Catalina
> 2005 JQ5 is the largest - and therefore most potentially devastating -
> of the 70 objects now being tracked. However, the chances of a collision
> are very low.
>
> The listing of Comet Catalina underscores the uncertainty in the
> knowledge of whether comets or asteroids pose a greater threat to Earth.
> Previous estimates of the proportion of the impact risk posed by comets
> have varied widely, from 1% to 50%, with most recent estimates at the
> lower end.
>
> But comets are larger and faster-moving, on average, so their impacts
> could be a significant part of the overall risk to human life. And,
> unlike asteroids, they lie on randomly-oriented and usually highly
> elongated orbits. This makes them much more likely to remain
> undiscovered until they are very close to Earth.
>
> Comet Catalina was found by the Catalina Sky Survey, one of the six
> current, large-scale and automated search programmes for near-Earth
> asteroids. It was initially designated as an asteroid when first spotted
> on May 6. But was reclassified as a comet when observers saw
> characteristic fuzziness in the image, indicating ice and dust streaming
> off.
>
> Its size is estimated at 980 metres, but Steve Chesley of JPL told New
> Scientist that the size determination is based on the assumption it is a
> dark-bodied asteroid, and so the bright coma of a comet would cause the
> estimate to be high. "It's really an upper limit," he said.
>
> Collision course?
>
> On 26 May, JPL's unique orbital calculation software determined that
> Comet Catalina was on what could possibly be a collision course with
> Earth, though the odds of such an impact were small: just 1 chance in
> 300,000 of a strike on June 11, 2085. Based on the 980-metre size
> estimate, that would produce a 6-gigaton impact - equivalent to
> 6 billion tonnes of TNT.
>
> Astronomers expected the addition of further observations to the
> calculations to rule out any possibility of a collision, as happens with
> most newly-seen objects.
>
> But that did not quite happen. The comet's predicted pathway actually
> drew even closer to making a perfect bull's-eye with the Earth - its
> predicted path passes within 1000 kilometres of the where the centre of
> our 12,700-km-diameter planet will be around that time.
>
> However, uncertainty in the exact timing of the comet's pass through the
> line of Earth's orbit dropped the odds of an impact to about 1 in 120
> million. That is very low, but the observations so far cannot
> categorically rule a collision out.
>
> Forceful outgassing
>
> Chesley adds that even the slim 1 in 120 million odds are an
> overestimate, because comets, unlike asteroids, can move in
> unpredictable ways because of the forceful outgassing that creates their
> dusty comas and tails. "The uncertainty is much larger than we're
> modelling," he said. "But I haven't come up with a good way of dealing
> with this."
>
> The only other comet placed on the JPL list of near-Earth objects with
> possible collision paths was added in 2003. But additional observations
> ruled out a possible impact - that comet was removed from the list after
> less than a week.
>
> Just one other comet, Swift-Tuttle, has been recorded with a non-zero
> possibility of impact. It was rediscovered in 1992 - after more than a
> century's absence - before the JPL list was created.
>
> Additional observations during Swift-Tuttle's passage, thanks to the
> publicity surrounding the possible impact, made it possible to rule out
> the possibility of an Earth impact anytime in this millennium. However,
> Swift-Tuttle is on an orbit that will almost certainly cause it to crash
> into the Earth or the moon eventually.