from smellslikehumanspirit.com: “When an asteroid exploded over the Russian city of Chelyabinsk in February,
shattering windows for miles and injuring well over 1,000 people,
experts said it was a rare event — of a magnitude that might occur only
once every 100 to 200 years, on average.

But now a team of scientists is suggesting
that the Earth is vulnerable to many more Chelyabinsk-size space rocks
than was previously thought. In research being published Wednesday by
the journal Nature, they estimate that such strikes could occur as often
as every decade or two.

The prospect “really makes a lot of people uncomfortable,” said Peter G. Brown, a professor of physics and astronomy at the University of Western Ontario and an author of the two studies in
Nature. A third paper by other scientists describing the Chelyabinsk
explosion was published online this week by the journal Science.

The findings are helping to elevate the topic
of planetary defense — identifying dangerous asteroids and deflecting
them if necessary — from Hollywood fantasy to real-world concern.”