When an asteroid exploded over Chelyabinsk, Russia last year it led to some astonishing videos. It is also proving a boon for science, with a new paper putting together the pieces to explore the history of the object responsible.
The asteroid explosion was brighter than the sun for 100km around and generated the second largest airburst recorded. The widespread availability of recording equipment, and the proximity to heavily populated areas meant that vision was available from multiple angles, as demonstrated in this video.
Consequently, scientists were quickly able to establish its size (17-20m) and trajectory to an unprecedented level of accuracy for such a major event. Moreover, fragments have been collected which have been studied around the world. These have been used to indicate the asteroid was a break-away from the 200m wide asteroid 2011 EO40.
Shin Ozawa, a graduate student at Tohoku University Sendai has published a paper in Scientific Reports providing insight into the history of the meteorite's progenitor. Ozawa found the presence of jadeite in the shock-melt veins others had already identified within the meteorites. Jadeite requires very high pressures to form.
The composition of the jadeite indicates that it was produced very rapidly, but the pressure lasted longer than 70ms. The speed and pressures involved indicated it was the product of two asteroids at least 150m across colliding at relative speeds of 0.4-15.km/s. While such a collision could happen anywhere in the solar system, it is much more in keeping with what occurs in the main asteroid belt than anywhere else.
Other researchers had previously concluded that the shock-melt forming collision happened 290 million years ago, although an earlier event took place not long after the solar system was formed. The jadeite would have been destroyed by subsequent collisions, indicating the asteroid had lived a very peaceful life for almost 300 million years before its fiery end. “The impact event studied here might have occurred at or after 290 Ma ago, and the Chelyabinsk asteroid probably separated from its parent body at this event,” Ozawa and his coauthors conclude.
Objects in the main asteroid belt that get into orbital resonance with Jupiter (for example taking a third as long to orbit the sun so that at every third orbit Jupiter is tugging at them at the same location) get pulled out within ten million years. From there they are usually thrown into orbits that send them into the sun, or cause them to collide with one of the planets. Consequently, Ozawa and his colleagues conclude, “The Chelyabinsk asteroid blasted off from its parent body could have moved into an orbital resonance at <10Ma ago, and then been delivered into an Earth-crossing orbit.”
By learning how Near-Earth Objects form, Ozawa hopes to help us understand the danger posed to the Earth by such objects. The Chelyabinsk event injured more than 1000 people, but fortunately killed no one, despite releasing more energy than the Hiroshima bomb. Next time we may not be so lucky.
(a) The host-rock of the Chelyabinsk meteor. (b) A shock-melt vein cutting through the host-rock. (c) Coarse-grained fragments and fine-grained matrix in a shock-melt vein. (d) Enlarged view of the area shown by the white rectangular in (c). Needle-like and skeletal-rhombic crystals of jadeite occur with feldspathic glass.