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on october sixth 2008 we discovered a

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near-earth asteroid about the size of a

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Volkswagen and we determined that it

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would hit the Earth's atmosphere at 746

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pacific daylight time over the northern

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sudan region of northern africa and at

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that location of course it would be for

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46 in the morning in the pre-dawn sky

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well it was discovered the way these

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near Earth objects are always discovered

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we take a CCD image just like you would

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with your camera of a certain region of

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the sky come back to that region 15

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minutes later take another image come

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back to that same region 15 minutes

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later take a third or fourth image and

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then we compare the images to see if any

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of the objects in those images have

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moved and if they have there almost

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certainly near-earth objects these

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objects are tiny and they're dark and

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because they're tiny and dark they're

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very very faint and we can only discover

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them when they're fairly close to the

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earth when they're not nearly as faint

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as they usually are so when they get

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close to the earth they're easy as to

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discover their motions on the sky our

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fastest and so that's the time when we

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typically discovered near Earth objects

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when they're fairly close to the earth

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why are we so confident this object the

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size of a Volkswagen is not going to

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punch through the atmosphere and hit the

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ground well what happens is that most of

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these objects are stony objects and what

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happens when they reach about 30 miles

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into the atmosphere coming down the

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pressure on the front side of that stony

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object is so much greater than the

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pressure on the backside that they

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pancake and fragment and dissipate in

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the Earth's atmosphere and so what you

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what you see is a fireball event or a

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bolide event and this this object

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fragments into a zillion pieces and then

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simply dissipates or burns up in the

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Earth's atmosphere without any of the

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fragments reaching the ground well this

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is a discovery that's big on a number of

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points first of all it's a it's a

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prediction of a very bright fireball of

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men so people can go out there and set

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up their equipment and get ready for it

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whereas usually a fireball is observed

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by people who just serendipitously are

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looking up at the right time

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so now we have a prediction suggesting

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one and this will occur so this suggests

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that the telescopic surveys that nASA

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has in place the orbit computation and

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impact probability calculations that

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NASA now has in place are working rather

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well because we were able to discover

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and predict exactly where this object

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would hit in a matter of a couple of

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hours and get it out on the web to the

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folks who need to know so I'm pleased

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that the system is working so well it

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just shows that NASA's ability to track

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to discover and track these objects is