The Russian Academy of Sciences estimates the meteor had a mass of 10,000 tons, entered atmosphere at speed 15 km/s and exploded when 30-50 km up. NASA estimated it was 17 meters diameter and 10,000 tons with an energy release equivalent to roughly 500 kilotons of TNT. Only a small fraction of this mass actually hit the ground, most must have vaporized. The fireball in the videos is very bright, substantially exceeding the sun for a short time; most of the damage was caused by the blast wave breaking glass, I saw a press estimate of a million sq.ft. of sheet glass destroyed. My belief is there is a threshold size, when the meteor's mass is about the same as the column of atmosphere including the meteor, and only meteors above this threshold survive to reach the ground. The NASA estimate exceeded my crude threshold by a factor about 5, which probably means "about the same" should be revised to "about 10 times"... but the threshold depends on what the meteor is made of and what angle it comes in at, and in this case the angle was fairly near horizontal. -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)