The most likely cause was a low-density comet, 0.7 miles (1.1 kilometres) wide, that broke up at an altitude of 43 miles and fell in pieces to Earth, the scientists reported in Astronomy Magazine.
They wrote: The main mass of the projectile struck the ground at 2,200 miles per hour, releasing an amount of energy equivalent to 106 million tons of TNT.
The bomb that destroyed Hiroshima at the end of the Second World War had an explosive force of just 20,000 tons of TNT.
The explosion they describe is in the kiloton range. To get megatons the main body would have to strike the ground in the 60,000 miles per hour range, not 2,000.