Russian meteor shockwave circles world twice
A meteorite strike that hit Russia in February was so powerful that scientists say it created a shockwave that travelled twice round the globe.
They used a system of sensors normally set up to detect evidence of nuclear tests.
Researchers say it was the most powerful event ever recorded by the network.
More than 1,000 people were injured when a 17 metre, 10,000-tonne rock burned up above Chelyabinsk, Russia.