First pre-impact detection of meteor (APOD 2008 Nov 08)

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Expand view Topic review: First pre-impact detection of meteor (APOD 2008 Nov 08)

Re: First pre-impact detection of meteor (APOD 08 Nov 2008)

by Dr. Skeptic » Sat Nov 08, 2008 10:59 pm

Oh NO! Enterprise to Captain ... Enterprise to Captain!!!!

Re: First pre-impact detection of meteor

by Chris Peterson » Sat Nov 08, 2008 10:20 pm

Dr. Skeptic wrote:It's the objects in or near the Kuiper belt that have their orbits disrupted by the mighty gas giants that will catch us by surprise. Imagine a Shoemaker like comet heading our way with a 30 to 60 day notice.
In fact, we could have no notice at all. A long period comet, or a new comet thrown into the inner system, would probably be detected at least a few months before impact... if it were in the night sky. But it could as easily come from the part of the sky the Sun is in, and the first time we'd see it would be when it started burning in the atmosphere, a few seconds before impact.

I don't know if it makes any difference, no notice vs. a few months. Not much could be done. At least with identified asteroids, it's possible to make a reasonable assessment of danger years in advance, which is plenty long enough to do something about it.

Re: First pre-impact detection of meteor (APOD 08 Nov 2008)

by astrolabe » Sat Nov 08, 2008 9:18 pm

Hello Nereid,

Good point, emissivity is a function of surface composition especially at IR wavelengths. At least that's true WRT thermal imaging of objects that are Earth bound.

Re: First pre-impact detection of meteor (APOD 08 Nov 2008)

by Nereid » Sat Nov 08, 2008 8:59 pm

I think that chart is for NEOs estimated to be >~1 km in diameter ("large", I guess); there is another chart at that site which shows the total number of objects being discovered, per year, is still high, and rising.

There's a bit of squishiness in the definitions ... size is (often? nearly always??) estimated from brightness, assuming a fixed albedo; if an object has a low albedo, it may be estimated to be well under 1 km, but in fact be considerably bigger. Unfortunately for us, low albedo objects may include some with rather high densities, making them more dangerous!

Re: First pre-impact detection of meteor

by iamlucky13 » Sat Nov 08, 2008 8:04 pm

NEO says objects like this strike several times per year. They also have a very detailed article about the detection, predictions, and observations, including a shot from a weather satellite that detected the event:

http://neo.jpl.nasa.gov/news/2008tc3.html
Dr. Skeptic wrote:It's the objects in or near the Kuiper belt that have their orbits disrupted by the mighty gas giants that will catch us by surprise. Imagine a Shoemaker like comet heading our way with a 30 to 60 day notice.
I suppose if anything, that's true, but such comets are far more rare than inner solar system asteroids. For those, we're running out of large objects to discover. Notice the declining rate, despite the improvements in the last decade in the quality NEO's observational capacity:

Image

http://neo.jpl.nasa.gov/stats/

Re: First pre-impact detection of meteor

by apodman » Sat Nov 08, 2008 7:39 pm

Dr. Skeptic wrote:Imagine ...
http://en.wikipedia.org/wiki/The_Paradise_Syndrome wrote:Kirk becomes himself again and flicks his communicator open to contact the ship. As soon as it makes a noise, the door to the obelisk is opened. Spock goes inside and repairs the deflector beam. The device, employing power exponentially greater than that of the Enterprise, targets the asteroid and successfully diverts it away from the planet, just minutes before collision.
Whew!

Re: First pre-impact detection of meteor

by Dr. Skeptic » Sat Nov 08, 2008 7:03 pm

Most of the asteroids capable of doing cataclysmic damage have been identified. A bigger concern with respect to large impactors is comets, which can literally come out of the blue without ever being detected. The goal with near-Earth asteroid monitoring is to reduce the size of object we can detect. 10 meters is about the minimum size that can make it to the ground carrying cosmic velocities; 50-100 meters is about the size object that can produce a crater like that in Arizona.
It's the objects in or near the Kuiper belt that have their orbits disrupted by the mighty gas giants that will catch us by surprise. Imagine a Shoemaker like comet heading our way with a 30 to 60 day notice.

Re: First pre-impact detection of meteor

by Chris Peterson » Sat Nov 08, 2008 2:50 pm

orin stepanek wrote:I think that most dangerous asteroids are monitored.
Most of the asteroids capable of doing cataclysmic damage have been identified. A bigger concern with respect to large impactors is comets, which can literally come out of the blue without ever being detected. The goal with near-Earth asteroid monitoring is to reduce the size of object we can detect. 10 meters is about the minimum size that can make it to the ground carrying cosmic velocities; 50-100 meters is about the size object that can produce a crater like that in Arizona.
I was wondering why the trail was so crooked? Was it because of atmospheric disturbances?
Yes, the image may have been taken an hour or more after the meteor. The fireball itself would have shown a completely straight tail, lasting a few seconds (like all fireballs). The object was big enough to deposit a lot of dust high in the atmosphere, which was subsequently blown around. There are quite a few images of dust clouds like this after big meteors. The smoke trail left by a rocket launch shows a similar sort of development.

Re: First pre-impact detection of meteor

by astrolabe » Sat Nov 08, 2008 1:57 pm

Hello All,

Great site for keeping an eye on these objects:
http://neo.jpl.nasa.gov/ca/

Re: First pre-impact detection of meteor

by orin stepanek » Sat Nov 08, 2008 1:43 pm

http://apod.nasa.gov/apod/ap081108.html

I think that most dangerous asteroids are monitored. Still there is always that one that may have not been discovered.
I was wondering why the trail was so crooked? Was it because of atmospheric disturbances? :? :

Orin

First pre-impact detection of meteor (APOD 2008 Nov 08)

by JohnD » Sat Nov 08, 2008 1:00 pm

That's exciting, but depressing, because it's going to happen. As Ms.Lakawalla says:

"what would have happened if the object was much bigger than 2 meters in diameter? Reassuringly, the first thing that would have happened is that the detection most likely would have happened much earlier. The bigger and more hazardous an object is, the brighter it is, and the sooner we will detect it. We will likely have way more than 20 hours' warning of an incoming dangerous object. Still, though, the warning time for a tens-of-meter-di ... ed in days. If we'd had three days' warning of a dangerous impactor heading for Sudan, what could the world have done? The remote location of the impact would have been fortunate for humanity in general, but disastrous for the few people who lived out in that remoteness."

My underlining.

John

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