Key points from article :
Space rock exploded with 10 times the energy released by the Hiroshima atomic bomb.
The blast (173 kilotons) was the second largest of its kind in 30 years.
40% the energy release of Chelyabinsk meteor in 2013.
Not spotted by NASA's near-Earth objects observations programme.
Went largely unnoticed because it blew up over the Bering Sea.
A fireball this big is only expected about two or three times every 100 years.
Space rock was several metres in size and exploded 25.6km above the Earth's surface.
Shows that large objects can collide with us without warning.
