The collision of Earth with a cosmic body over Chelyabinsk – Czech
astronomers publish new results in the prestigious journal Nature
Press release from November 6, 2013, translation from Czech
The prestigious journal Nature is publishing today the paper “Trajectory, structure, and origin of the
Chelyabinsk asteroidal impactor” under the leadership of Czech
astronomers from the Department of Interplanetary Matter of the
Astronomical Institute of the Czech Republic. The entry of a small
asteroid over Russia on February 15 this year attracted world-wide
attention. Many scientific teams are now analyzing this rare event.
Czech astronomers have been working on it from the very beginning. As
the first team, already on February 23, they published the trajectory
of the body obtained by a rigorous method. In the new paper, the
trajectory and velocity is further refined, the deceleration and
fragmentation of the body in the atmosphere is studied, and the
development of the dust trail left in the atmosphere after the passage
of the body is described. The refined heliocentric orbit proved to be
very similar to the orbit of asteroid 86039 (1999 NC43), a Near Earth
Asteroid of diameter larger than 2 km. In collaboration with Canadian
astronomers, who are co-authors of the paper, it was shown that the
there is only a 1:10,000 probability that the similarity of the orbits
is due to pure chance. It is therefore likely that the Chelyabinsk
asteroid and asteroid 86039 were once part of the same body.
Full list of authors of the paper in
Nature
Jiří Borovička1, Pavel Spurný1,
Peter Brown2,3, Paul Wiegert2,3, Pavel Kalenda4,
David
Clark2,3 and Lukáš Shrbený1
1Astronomical Institute, Academy of Sciences of the Czech
Republic, CZ-251 65 Ondřejov, Czech Republic
2Department of Physics and Astronomy, University of Western
Ontario, London, Ontario N6A 3K7, Canada
3Centre for Planetary Science and Exploration, University of
Western Ontario, London, Ontario N6A 5B7, Canada
4Institute of Rock Structure and Mechanics, Academy of
Sciences of the Czech Republic, V Holešovičkách 41, CZ-18209
Praha 8, Czech Republic
What is new
The new computation of the trajectory was possible thanks to the
calibrations of 15 video records of the bolide. The video records are
freely available on the Internet. Nevertheless, it was necessary to
visit the sites, where the videos were taken, and take photos of the
same scenes again, together with a starry night sky. Most of this key
work was done by Mr. David Částek. He was installing industrial
machines in Korkino near Chelyabinsk on February 15 and was a direct
witness of the blast wave which affected this region and caused
substantial damage. He wrote an e-mail to Dr. Pavel Spurný from
the Astronomical Institute, who asked him to make the calibrations. Dr.
Lukáš Shrbený from the Astronomical Institute and Dr.
Pavel Kalenda from the Institute of Rock Structure and Mechanics also
took part in the searching and locating of the suitable video and
preparing the calibrations. The trajectory was computed by Dr.
Jiří Borovička from the Astronomical Institute. The resulting
trajectory parameters are not very different from the preliminary
results obtained in February, nevertheless, the trajectory was
determined with higher precision. New studies considered the curvature
of the trajectory due to Earth’s gravity and the trajectories of
individual fragments emerging after asteroid disruption. Dr. Borovička
modeled the disruption using the bolide light curve and deceleration.
For the locations of the break-ups, the times of arrivals of sonic
booms at various sites in Chelyabinsk and surroundings, as recorded on
videos, were also used. Dr. Pavel Kalenda from the Institute of Rock
Structure and Mechanics and Dr. Peter Brown from the University of
Western Ontario in Canada participated in the sonic analysis.
It was found the Chelyabinsk asteroid
was a relatively fragile body. Its disruption started already at
the height of about 45 km above ground. At the height of 30 km, 95% of
the ~19 meters wide asteroid was already converted into dust and small
fragments. The rest existed in the form of about twenty boulders with
the sizes of few meters. The boulders disrupted dramatically at the
heights of 25 – 20 km. Only tiny fraction of the original mass reached
the ground, mostly in the form of small fragments. Just one large
fragment survived the atmospheric passage. The calculations confirmed
that it landed into the Chebarkul Lake. The impact hole was discovered
soon after the event. The fragment was finally pulled out of the lake
bottom on October 16. Its mass was 650 kg. The initial mass of the
asteroid was approximately 12 thousands metric tons and the diameter
was about 19 meters. The probable reason of the fragility was the
presence of many cracks in the material, a consequence of previous
collisions with other asteroids.
The larges response is expected over the likely connection with asteroid 86039.
The
calculations
of
Dr. Paul Wiegert and Dr. David Clark from the
University of Western Ontario showed that the orbits of both asteroids
are intersecting and this was the case also in the past, at least for
several thousands of years. It is therefore quite possible that the
Chelyabinsk asteroid was excavated from asteroid 86039 during a recent
(in comparison with the age of the Solar System) collision with another
asteroid. More bodies on similar orbits could be created during that
collision. Further research must say if that was the case.
In the same issue of Nature, the paper “A 500-kiloton airburst over Chelyabinsk
and an enhanced hazard from small impactors” is published. The
first author is Peter Brown; Jiří Borovička and Pavel
Spurný are the members of the author team. In that paper, the
energy of the airburst over Chelyabinsk was computed. It was more than 30 times higher than the energy
of the Hiroshima atomic bomb. It is also suggested that the
frequency of collisions with asteroids in the size range 10-50 meters
may be up to 10 times higher than previously thought.
Nearly at the same time, the journal Science will publish a paper of
other authors on the same topic. These three papers together represent
the top what the world science could say to the Chelyabinsk event to
date.