Russian meteor largest in a century
Explosion rivalled nuclear blast, but rock was still too small for
advance-warning networks to spot.
* Geoff Brumfiel
15 February 2013 Corrected:
1. 15 February 2013
A meteor that exploded over Russia this morning was the
largest recorded object to strike the Earth in more than a century,
scientists say. Infrasound data collected by a network designed to watch for
nuclear weapons testing suggests that today's blast released
hundreds of kilotonnes of energy. That would make it far more powerful
than the nuclear weapon tested by North Korea just days ago and the
largest rock crashing onto the planet since a meteor broke up over
Siberia's Tunguska river in 1908.
"It was a very, very powerful event," says Margaret
Campbell-Brown, an astronomer at the University of Western Ontario in
London, Canada, who has studied data from two infrasound stations near
the impact site. Her calculations show that the meteoroid was
approximately 15 metres across when it entered the atmosphere, and put
its mass at around 7,000 metric tonnes. "That would make it the biggest
object recorded to hit the Earth since Tunguska," she says.
Hidden approach
The meteor appeared at around 9.25 a.m. local time over
the region of Chelyabinsk, near the southern Ural Mountains. The
fireball blinded drivers and a subsequent explosion blew out windows and
damaged hundreds of buildings. So far, more than 700 people are
reported to have been injured, mainly from broken glass, according to a
statement from the Russian Emergency Ministry.
Expand
The meteor contrail seen over Chelyabinsk, Russia, on 15 February. The
object's explosion in the atmosphere is reported to have injured more
than 700 people.
Chelyabinsk.ru/AP
Despite its massive size, the object went undetected until it hit the
atmosphere. "I'm not aware of anyone who saw this coming,"
says Heiner Klinkrad, head of the European Space Agency's space debris
office at the European Space Operations Centre in Darmstadt, Germany.
Although a network of telescopes watches for asteroids that might strike Earth,
it is geared towards spotting larger objects — between 100
metres and a kilometre in size.
"Objects like that are nearly impossible to see until a
day or two before impact," says Timothy Spahr, director of the Minor
Planet Center in Cambridge, Massachusetts, which tracks asteroids and
small bodies. So far as he knows, he says, his centre also failed to
spot the approaching rock.
The meteoroid itself was probably made of rock, but may
have also contained nickel and iron. Campbell-Brown says that it was
likely to have come from the asteroid belt, a region containing hundreds of
thousands of rocky bodies and located between Mars and Jupiter. The
European Space Agency does not think that the meteor is related to a
much larger asteroid known as 2012 DA14, which will be passing within about
20,000 kilometres of Earth later
today. Both the timing of the meteor's appearance and its location
indicate that it came from a different direction, Klinkrad says.
Campbell-Brown agrees: "We happened to have close approaches to two of
them, and one of them got us," she says.
Shockwave
Related stories
* US meteorite was fastest on record
* Astronomers lose access to military data
* Astronomy: The rock that fell to Earth
More related stories
Although there are reports of fragments of the meteor, or meteorites, striking
the ground, Klinkrad says that he believes the vast majority of damage
in the region was caused by shockwaves of the explosion, as the rock
broke up in the upper atmosphere. Campbell-Brown says that the
infrasound data shows a very shallow angle of approach — a feature that
funnelled much of the energy from the blast to the city below. Still,
she adds, "It's lucky that there wasn't more damage."
The infrasound stations belonged to the Comprehensive Test Ban Treaty
Organization, an international body that is designed to watch the Earth for
nuclear-weapons tests. It is unlikely to be the only source of data on
the strike. Both the United States and Russia have satellites in
geosynchronous orbit that watch for the heat signatures of missile
launches and warhead re-entries. The US military has released data on meteor
strikes in the past, but it is unclear whether they will do so for today's
event.
Klinkrad says it would have been hard to give warning of
the blast. In addition to being relatively small in size, the rocky
meteoroid was probably dark in colour, making it even harder to spot
against the backdrop of space. "We just have to live with it," he says.
http://www.nature.com/news/russian-meteor-largest-in-a-century-1.12438
[Non-text portions of this message have been removed]
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