The Sciences

BREAKING: Sofa-sized asteroid gives us a close shave

Bad AstronomyBy Phil PlaitFeb 4, 2011 5:21 PM


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As I write this, in less than a half hour (at 19:40 UT) an asteroid 1-2 meters in size will pass about 12,000 5500 km from the Earth's surface: less than 7500 3500 miles! The Earth itself is 13,000 km across, so this is a close shave indeed.

[UPDATE: Turns out the miss distance of 12,000 km was measured from the Earth's center. Subtracting our radius of about 6400 km, the rock actually came about 5500 km from our surface -- so, even closer than I originally thought. Sorry about the error, and thanks to Emily at The Planetary Society Blog where I saw the actual number.]

Still, it will miss, and would not be dangerous even if it did hit us.

Got that? Cool. This rock, officially named 2011 CQ1, was discovered just last night! Here's a shot of it taken using a small 0.35 meter (14") telescope at the Tzec Maun Observatory in New Mexico:

This is a combination of 20 short exposures tracking the asteroid; the stars appear as dotted lines while the asteroid itself as the indicated dot. Now let me be clear: this rock will miss us, and even if it had been aimed at us it would be unlikely in the extreme to do any damage. It's way too small. Most likely were something like this to hit us, it would explode very high in the Earth's atmosphere, releasing as much energy as perhaps a ton or so of TNT. That may sound like a lot, but it's actually not a big deal. Some estimates have us getting hit by meter-size rocks once per month or so. The fact that you never hear about them indicates they are no danger! It would take something far bigger to hurt us. The rock that blew up over Tunguska in 1908 was probably 30 meters or so in size; that detonated with a yield of about 15 - 20 megatons of TNT, equivalent to a pretty big nuke (though without radiation). Something metallic that size would probably hit the ground intact, leaving a hole like Arizona's Meteor Crater, which is over a kilometer across. Happily, impacts like that are extremely rare! Smaller ones are more common. In late 2008, a smallish rock about the same size as 2011 CQ1 came in over the Sudan and exploded, raining down small rocks which were later recovered. No one was hurt. So the point here is that CQ1 is too small to hurt us even if it were to hit, which it won't. And the cool thing is that it was seen at all! Two meters is dinky indeed, and this kind of discovery, far from being scary, makes me happy because it means we're getting better all the time at detecting rocks that might actually hit and do damage.

Image credit: Giovanni Sostero & Ernesto Guido. Tip o' the Whipple Shield to reddit.

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