Posted on 06/02/2005 9:48:00 PM PDT by IllumiNaughtyByNature
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.
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 about 1 kilometre but Steve Chesley of JPL told New Scientist that this "could be off by a factor of a few" in either direction. If there is enough dusty coma to increase its brightness significantly, the nucleus itself might only be a few hundred metres across. But if there is very little dust, then because comets are quite dark, the nucleus could be larger than estimated, perhaps a few kilometres across, Chesley said. "So 1 kilometre is pretty much in the middle of the reasonable range."
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 1 kilometre size estimate, that would produce a 6-gigaton impact - equivalent to 6 billion tonnes of TNT.
Astronomers expect 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 has not quite happened yet. With an extra week of data, the comet's predicted pathway actually drew even closer to making a perfect bull’s-eye with the Earth - its predicted path passes within 400 kilometres of 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 odds therefore might be wrong "by a factor of two or so" he said. The cut-off for inclusion on the list is 1 in 10 billion.
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.
Yeah, I'll be 112 when (if?) it hits.
So a ball of dust and Ice of that size would likely succumb to your run of the mill nuclear warhead, No?
Probably easier shoved with an attached propulsion device.
We should have tech like that by 2085.
/tin-foil hat guessing game post
That's right we can't blow it up, GreenSpace will have replaced GreenPeace and they'd be all over us for that and it would be Bush's fault back in 05
Deep Impact will have such negligable trajectory effects on Tempel, its really not worth mentioning.
Cannonball-Gnat sort of thing.
No. It'd take a number of specialized nukes, carefully placed in space some distance from the comet.
Except that no one has any firm idea of how solid comets are, and therefore no clue on how to attach such a device.
:')
Comet put on list of potential Earth impactors
New Scientist | 1 June 2005 | David L Chandler
Posted on 06/02/2005 9:04:31 AM PDT by SunkenCiv
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