The shock waves from what appear to have been multiple blasts, perhaps triggered as large initial fragments underwent their own disruption, broke windows in the three major cities in the region, including Chelyabinsk. At least 950 people were injured, although most of the injuries were minor, according to reports from the area.
"What an amazing day for near-Earth objects. By an incredible coincidence we have two rare events happening on the very same day," Dr. Chodas said during a briefing Friday afternoon.
Asteroid 2012 DA14 set a record for the closest approach to Earth of an asteroid in its size class humans so far have detected. And the Chelyabinsk blast occurs on average once every hundred years, based on the revised size and mass estimate for the asteroid that triggered it.
The new estimates of the Chelyabinsk asteroid come courtesy of a network of exquisitely sensitive barometers that pick up subtle vibrations in the air at frequencies below the those of human hearing. In effect, they are the atmospheric equivalent of seismographs, which detect earthquakes large and small.
Arrays of these sensors were set up at 60 locations around the world to monitor for violations of the Comprehensive Test Ban Treaty's ban on atmospheric nuclear-weapons tests. Researchers can use the signals these sensors pick up to estimate the energy released in an explosion. That release, in turn, allows for estimates of the asteroid's mass.
Although the Chelyabinsk event probably was recorded by many of the arrays, the new estimates of the asteroid's size and explosive yield came from the four closest arrays, Dr. Cooke of Marshall Space Flight Center says.