Papers this week in Science and Nature journals describe studies of the Chelyabinsk meteor fireball last February. One paper estimates that the meteoroid was twice as massive as originally estimated. A Science paper combines Chelyabinsk with the Tunguska event in Siberia in 1908 to estimate that the rate of such impacts is as much as ten times higher than previously thought.

• Hazardous asteroids may be more numerous than previously thought, scientists say – The Washington Post
• Siberian Blast Points to More Destructive Meteors Ahead –  Science/AAAS
• Risk of massive asteroid strike underestimated: Meteor in Chelyabinsk impact was twice as heavy as initially thought. – Nature

A Nature video report on the Chelyabinsk studies: