On Feb. 15, when a 10,000 ton space rock slammed into the atmosphere over the city of Chelyabinsk, Russia, injuring over 1,500 people and causing millions of dollars in property damage, the world suddenly became aware that our planet lives in a cosmic shooting gallery. We had suffered a planetary flesh wound. Almost immediately after the event, the question on everyone's mind was: When will the next asteroid hit?
Now, according to some complex orbital dynamics modeling, scientists have come up with a rather unsettling hypothesis - what if the Chelyabinsk asteroid wasn't alone?
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In a paper accepted for publication in the journal Monthly Notices of the Royal Astronomical Society: Letters, brothers Carlos and Raúl de la Fuente Marcos at the Complutense University of Madrid have run exhaustive computer simulations of the Chelyabinsk asteroid orbit before it hit us and tried to deduce where it came from. In doing so, they may have identified similar objects that pose a risk.
"More objects with the same orbital signature may encounter our planet in the future," Carlos de la Fuente Marcos told Nature News.
The problem with the Chelyabinsk meteor is that it wasn't spotted before it hit. The asteroid was masked by the glare of the sun - an obvious weak spot exploited by WWII fighter pilots and hazardous asteroids alike. So in an effort to not be caught off guard again, the de la Fuente Marcos brothers matched their "best fit" orbital models and compared them with known asteroid orbits from NASA databases. From this work, they suspect the Chelyabinsk asteroid originated from another shattered asteroid where its pieces are still out there orbiting in a cluster - a gang of space rocks they collectively call the "Chelyabinsk cluster."
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"We find reliable statistical evidence on the existence of the Chelyabinsk cluster," the researchers write in the arXiv preprint of their publication. "It appears to include multiple small asteroids and two relatively large members: 2007 BD7 and 2011 EO40. The most probable parent body for the Chelyabinsk superbolide is 2011 EO40."
In other words, the Russian meteor may not have been alone when it was an asteroid orbiting the sun. The largest asteroid in the candidate cluster, asteroid 2011 EO40, is thought to measure approximately 200 meters across. The Chelyabinsk meteor may have been a fragment from this larger parent asteroid, suggestive that the larger asteroid fragmented at some point in its orbit.
However, the orbit of 2011 EO40 is, by its nature, rather precarious - it passes close to Venus Earth and Mars and will therefore experience gravitational perturbations, gradually scattering other asteroids in the cluster. It is for this reason that the researchers point out that for the Chelyabinsk cluster to be in existence today, the asteroid breakup likely occurred less than 40,000 years ago.
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Although interesting, other astronomers suspect that the projected orbit of the Chelyabinsk asteroid and its similarity to other known near-Earth asteroids is more of a coincidence rather than the smoking gun.
"I think that the resemblance of orbits is coincidental," said David Nesvorny, of the Southwest Research Institute in Boulder, Colorado. "It is not obvious to me why (the Chelyabinsk meteor) cannot be a fragment that was produced by a collision in the main asteroid belt, and evolved to its impact orbit by a few planetary encounters."
The de la Fuente Marcos brothers admit that further observations of asteroids in the candidate cluster are needed to refine their orbits, but the ideal method to confirm the nature of the Chelyabinsk meteor would be to compare samples of fragments of the Russian "superbolide" and compare it with samples returned from 2011 EO40. A cheaper, though less accurate, method would be to gather high-resolution spectra of reflected light off those objects in the hope of understanding their composition. Only then will the true nature of the destructive Chelyabinsk meteor be identified.
ArXiv preprint: "The Chelyabinsk superbolide: a fragment of asteroid 2011 EO40?", C. de la Fuente Marcos, R. de la Fuente Marcos, 2013. arXiv:1307.7918 [astro-ph.EP]
Image credit: The incoming meteor captured on the Russian vehicle's dashcam. Source: YouTube