|Panorama of the Chelyabinsk Fireball as it fell to earth on February 15, 2013. This is the smoke train left behind as the meteoroid, travelling at 40,000 mph, was incinerated by friction from the earth's atmosphere. The great heat, together with the huge differential pressure between the front and back of the meteoroid, caused it to explode about 12-15 miles above the earth. Click for full-size view.|
There is now speculation that the meteoroid may have been cometary in nature due to the bright white color of its trail, indicating water vapor rather than smoke arising from seared rock or metal. In addition, the trajectory, a pair of trails close together, spreading out, then comping back together is indicative of an object smoking from two ends of a single projectile, not one that blew apart. If it had blown apart it would not be seen to merge again later.
So, for now this meteoroid is speculated to be an icy, cometary body emitting steam from two ends as it is heated in the earth's atmosphere, spinning as it falls to earth.