…may be more common than we thought:

The scientific orthodoxy said that a Chelyabinsk-size event ought to happen every 140 years or so, but Brown saw several such events in the historical record.

Famously, a large object exploded over the Tunguska region of Siberia in 1908. But there have been less-heralded impacts, including one on Aug. 3, 1963, when an asteroid created a powerful airburst off the coast of South Africa.

“Any one of these taken separately I think you can dismiss as a one-off. But now when we look at it as a whole, over a hundred years, we see these large impactors more frequently than we would expect,” said Brown, whose paper appeared in Nature.

But our response, and actions to become a space-faring civilization, remains pathetic.