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.