The skies over Tokyo were lit up by an explosive extraterrestrial object early Thursday morning that also came with a sonic boom, according to some reports. [...]
"We were able to calculate a source energy of the entering asteroid of about (165 tons or 150 metric tonnes) of TNT," reads an IMO blog post.
It was really fast with a speed of 15 km/s. The Japanese are lucky that it wasn't large enough to survive and hit Tokyo.