BBC News, Simon
Redfern, 28 June 2013
More than 1,000 people were injured in February's event - most were related to glass from shattered windows |
Related
Stories
- Q&A: Asteroid and comet impacts
- Russia meteor's origin tracked down
- Fire in the sky: Tunguska at 100
The shock
wave from an asteroid that burned up over Russia in February was so powerful
that it travelled twice around the globe, scientists say.
They used a
system of sensors set up to detect evidence of nuclear tests and said it was
the most powerful event ever recorded by the network.
More than
1,000 people were injured when a 17m, 10,000-tonne space rock burned up above
Chelyabinsk.
The study
appears in the journal Geophysical Research Letters.
The
researchers studied data from the International Monitoring System (IMS) network
operated by the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO).
The
detection stations look out for ultra-low frequency acoustic waves, known as
infrasound, that could come from nuclear test explosions. But the system can
also detect large blasts from other sources, such as the Chelyabinsk fireball.
Alexis Le
Pichon, from the Atomic Energy Commission in France and colleagues report that
the explosive energy of the impact was equivalent to 460 kilotonnes of TNT. This
makes it the most energetic event reported since the 1908 Tunguska meteor in
Siberia.
Irons in
the fire
Meanwhile,
another team of scientists has published a study focusing on the Tunguska
event.
Fallen trees still litter the Taiga forest near the site of the Tunguska airburst |
The
Tunguska air blast is estimated to have been equivalent to three to five
megatonnes of TNT, hundreds of times more energetic than the Hiroshima
explosion, and it flattened trees across 2,000 sq km of forest.
Victor
Kvasnytsya, from Ukraine's National Academy of Sciences, and colleagues studied
microscopic samples of mineral debris from the blast area that have been
trapped in peat.
In their
paper, they describe the mineralogy of samples recovered from the peat in the
1970s and 80s. High-resolution imaging and spectroscopy identified carbon
minerals such as diamond, lonsdaleite and graphite.
Lonsdaleite
in particular is found in carbon-rich material subjected to a shock wave, and
is typically formed in meteorite impacts.
The
lonsdaleite fragments contain smaller inclusions of iron sulphides and
iron-nickel alloys, troilite and taenite, which are also characteristic
meteorite minerals.
The iron to
nickel ratio and the precise combinations of minerals assembled in these small
fragments all point to a meteorite source, and are nearly identical to similar
minerals found in the Canyon Diablo meteor that impacted Barringer Crater
(Meteor Crater) in Arizona.
The
findings would appear to rule out a theory that the Tunguska airburst was
caused by a large fragment of Comet Encke. This comet is responsible for a
meteor shower called the Beta Taurids, which cascade into Earth's atmosphere in
late June and July - the time of the Tunguska event.
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