WASHINGTON (AP) — Scientists studying the terrifying meteor
that exploded without warning over a Russian city last winter say the
threat of space rocks smashing into Earth is bigger than they thought.
Meteors about the size of the one that streaked through the sky at 42,000
mph and burst over Chelyabinsk in February — and ones even larger and more
dangerous — are probably four to five times more likely to hit the planet
than scientists believed before the fireball, according to three studies
published Wednesday in the journals Nature and Science.
Until Chelyabinsk, NASA had looked only for space rocks about 100 feet
wide and bigger, figuring there was little danger below that.
This meteor was only 62 feet across but burst with the force of about 40
Hiroshima-type atom bombs, scientists say. Its shock wave shattered
thousands of windows, and its flash temporarily blinded 70 people and
caused dozens of skin-peeling sunburns just after dawn in icy Russia. More
than 1,600 people in all were injured.
Up until then, scientists had figured a meteor causing an airburst like
that was a once-in-150-years event, based on how many space rocks have
been identified in orbit. But one of the studies now says it is likely to
happen once every 30 years or so, based on how often these things are
By readjusting how often these rocks strike and how damaging even small
ones can be, "those two things together can increase the risk by an order
of magnitude," said Mark Boslough, a Sandia National Lab physicist,
co-author of one of the studies.
Lindley Johnson, manager of NASA's Near Earth Object program, said the
space agency is reassessing what size space rocks to look for and how
often they are likely to hit.
The U.S. government gained a new sense of urgency after Chelyabinsk,
quietly holding a disaster drill earlier this year in Washington that was
meant to simulate what would happen if a slightly bigger space rock
threatened the East Coast.
After the drill, NASA and Federal Emergency Management Agency officials
said they should look at the need for evacuations, figure out ways of
keeping the public informed without scaring them, and handle meteor
threats in a way comparable to how they deal with hurricanes bearing down
on the coast.
During the drill, when it looked as if the meteor would hit just outside
the nation's capital, experts predicted 78,000 people could die. But when
the mock meteor ended up in the ocean, the fake damage featured a 49-foot
tsunami and shortages of supplies along the East Coast, according to an
after-action report obtained by The Associated Press.
The exercise and the studies show there's a risk from smaller space rocks
that strike before they are detected — not just from the giant,
long-seen-in-advance ones like in the movie "Armageddon," said Bill Ailor,
a space debris expert at the Aerospace Corporation who helped coordinate
"The biggest hazard from asteroids right now is the city-busting
airbursts, not the civilization-busting impacts from 1-kilometer-diameter
objects that has so far been the target of most astronomical surveys,"
Purdue University astronomer Jay Melosh, who wasn't part of the studies,
wrote in an email.
"Old-fashioned civil defense, not Bruce Willis and his atom bombs, might
be the best insurance against hazards of this kind."
Scientists said a 1908 giant blast over Siberia, a 1963 airborne explosion
off the coast of South Africa, and others were of the type that is
supposed to happen less than once a century, or in the case of Siberia,
once every 8,000 years, yet they all occurred in a 105-year timespan.
Because more than two-thirds of Earth is covered with water and other vast
expanses are uninhabited deserts and ice, other past fireballs could have
This week, NASA got a wake-up call on those bigger space rocks that
astronomers thought they had a handle on, discovering two 12-mile-wide
space rocks and a 1.2-mile-wide one that had escaped their notice until
The three objects won't hit Earth, but their discovery raises the question
of why they weren't seen until now.
The last time a 12-mile-wide rock had been discovered was about 30 years
ago, and two popped into scientists' view just now, NASA asteroid
scientist Donald Yeomans said. He said NASA had thought it had already
seen 95 percent of the large space rocks that come near Earth.
Asteroids are space rocks that circle the sun as leftovers of failed
attempts to form planets billions of years ago. When asteroids enter
Earth's atmosphere, they become meteors. (When they hit the ground, they
are called meteorites.)
The studies said the Chelyabinsk meteor probably split off from a much
bigger space rock.
What happened in the Russian city of 1 million people is altering how
astronomers look at a space rocks. With first-of-its-kind video, photos,
satellite imagery and the broken-up rock, scientists have been able to
piece together the best picture yet of what happens when an asteroid
careens into Earth's atmosphere. It's not pretty.
"I certainly never expected to see something of this scale or this
magnitude," said University of Western Ontario physicist Peter Brown, lead
author of one study. "It's certainly scary."
Scientists said the unusually shallow entry of the space rock spread out
its powerful explosion, limiting its worst damage but making a wider area
feel the effects. When it burst it released 500 kilotons of energy,
"We were lucky. This could have easily gone the other way. It was really
dangerous," said NASA meteor astronomer Peter Jenniskens, co-author of one
of the papers. "This was clearly extraordinary. Just stunning."