Saturday, February 16, 2013

How big was the Chelyabinsk meteor?

There is a huge discrepancy in reports of the size of the Chelyabinsk meteor.  Some apparently reliable sources put it at 10-30 tons, while others have it at 7,000-10,000 tons.  This is an enormous discrepancy.  Can we figure out which one is correct?

All accounts agree that the speed of the meteor was 30,000-40,000 miles per hour, which is pretty much the going rate for meteors.  That works out to about 15,000 meters per second.  The kinetic energy of a moving object is 1/2 times the mass times the velocity squared.  For this rough calculation we can ignore the 1/2 (we're looking at a two-order-of-magnitude discrepancy here).  So a ten ton (10,000 kg) meteor moving at 15,000 m/s has an energy of about 10^12 Joules.  That's less than one kiloton of TNT, not nearly enough to cause the kind of widespread damage that was reported.

So the 7000-10,000 ton figure is almost certainly the correct one.


Tom Moore said...

This has been bugging me too. WTH!?

Tom Moore said...

The official NASA pages show the larger number, 7-10,000 tonnes, and 56 m in diameter. This is the size threshold for a "heavy cruiser", according to wikipedia. So it was the size of big ship!