Scientists in Canada say the threat of another asteroid strike like the one that hit Russia earlier this year is much higher than was previously thought.
A study published in the scientific journal Nature found that space rocks as big as a house, similar to the one that exploded over Chelyabinsk, are frequently hurtling into the Earth's atmosphere.
Most go undetected because they explode over remote areas or the ocean.
The study's lead scientist Peter Brown, from Western University in Ontario, says early warning systems should be put in place, the BBC reports.
"Having some sort of system that scans the sky almost continuously, looks for these objects just before they hit the earth, that probably is something worth doing," he says.
Professor Brown says in the case of Chelyabinsk, a few days or a week's warning would have been valuable, if for no other reason than to tell people to stay away from their windows when the asteroid came down.