Scientists say the danger of space rocks smashing into Earth is greater than they thought.
They began re-assessing the threat after a meteor exploded over a Russian city in February without warning. It flew through the sky at 42,000 miles an hour and exploded in the air with the force of 40 Hiroshima-type atomic bombs.
No one saw it coming because it came from the direction of the sun.
Now scientists say the biggest danger is from smaller space rocks, like the one that hit Russia, which was 62 feet wide.
Those rocks are far more likely to hit Earth than a bigger meteor and might be easily missed by astronomers. Though considered "small," if they hit, they could devastate cities.
One simulation showed such an impact in the right area could kill nearly 80,000 people.