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Near Earth Objects - DD45's Near Miss

I listened to  an interview with Professor Alan Fitzsimmons, Queens University Belfast  on the  the March 8 (2009)  Naked Scientist podcast from Cambridge.

Chris Smith  and Alan discuss DD45, "a small asteroid. It's about between 20-40m across. It was discovered only just over a week ago, on Friday 27th February. It passed our planet by at a distance of only 72,000km on Tuesday.
Chris - That's extremely close. That's, let's put that in perspective. Satellites orbit the Earth about 25,000 miles out. That's only twice as far away as a geostationary satellite.
Alan - That's right. Occasionally we do spot these small asteroids coming past us. Objects of that size hit the earth probably about once every 2-300 years. We're not quite sure how often they hit us at the moment but they hit us on time scales of centuries.
Chris - Had this thing not been seventy thousand kilometres away and it had actually landed on the Earth what sort of damage would it have done? How would it compare with, say, the object that wiped out the dinosaurs?
Alan - Well, it's much smaller than that. The object that wiped out the dinosaurs was about ten kilometres across and had global consequences. Those objects only hit us about once ever hundred million years. An object that can cause climate change can be as small as one kilometre across, however. Even they only hit us once every million years or so. Something this size may have been similar to the object that entered our atmosphere over Tunguska in Siberia in 1908. It may have exploded low down in the atmosphere if it had entered our atmosphere and perhaps about a few kilometres up. It would have wiped out several square thousand kilometres of ground."
You can download the MP3 of the interview here or listen to it on the podcast web page.  The interview was part of the 8th Mar 2009 - Your Questions and Swallowing Swords podcast.  I encourage you to subscribe to this podcast - it is always interesting!