On Feb. 15, the Urals region of Russia played host to a noisy cosmic visitor. A meteor entered the atmosphere and broke up over the city of Chelyabinsk, generating powerful shockwaves that slammed into the city, blowing out windows, causing 1,500 injuries and millions of dollars-worth of damage. Before it collided with Earth, however, the Chelyabinsk space rock was a 10,000 ton meteoroid and astronomers now think they know where it came from.
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Helped by the extensive coverage of eyewitness cameras, CCTV footage and a fortuitous observation made by the Meteosat-9 weather satellite, Jorge Zuluaga and Ignacio Ferrin of the University of Antioquia in Medellin, Colombia, have been able to reconstruct the most likely orbit of the space rock around the sun before the Earth got in its way. What's more, they know what type of space rock it was.
Using video evidence (most of which had precise timestamps), the location, speed and altitude of the fireball could be estimated. Add to that the location where a suspected meteorite fragment punched a hole into the ice of Lake Cherbakul and it's a case of using some simple math to learn the characteristics of the object. But to trace the meteoroid's path back out into space and assemble its orbital trajectory around the sun wasn't so straight forward, according to the arXiv blog.
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However, this analysis hinges on one important factor: "Assuming that the hole in the ice sheet of Lake Cherbakul was produced by a fragment of the meteoroid is also a very important hypothesis of this work. More importantly, our conclusions relies strongly onto assume that the direction of the trajectory of the fragment responsible for the breaking of the ice sheet in the Lake, is essentially the same as the direction of the parent body. It could be not the case. After the explosion and fragmentation of the meteoroid fragments could acquire different velocities and fall affecting areas far from the region where we expect to find," the researchers write in their paper submitted to the arXiv pre-print service. So far, no meteorite has been recovered from Lake Cherbakul.
"According to our estimations, the Chelyabinski meteor started to brighten up when it was between 32 and 47 km up in the atmosphere ... The velocity of the body predicted by our analysis was between 13 and 19 km/s (relative to the Earth) which encloses the preferred figure of 18 km/s assumed by other researchers," they add.
Armed with this wealth of data farmed from various eyewitness sources, they used a piece of software called NOVAS (an acronym for "Naval Observatory Vector Astrometry Software") developed by the U.S. Navy Observatory (USNO). This sophisticated program was able to consider the gravitational influence of the moon, plus eight other bodies in the solar system, ultimately helping Zuluaga and Ferrin track where the object was before impact.
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Taking its orbit into account, the researchers were able to conclude that the Chelyabinsk-bound meteoroid originated from an Apollo-class asteroid. Apollo asteroids are well-known near-Earth asteroids that cross the orbit of Earth. Around 5,200 Apollo asteroids are currently known, the largest being 1866 Sisyphus - a 10 kilometer-wide monster that was discovered in 1972.
Large Apollos are identified as being a significant risk to our planet, so the Chelyabinsk meteoroid acted like an Apollo warning shot.
Publication: A preliminary reconstruction of the orbit of the Chelyabinsk Meteoroid, Zuluaga and Ferrin, arXiv:1302.5377 [astro-ph.EP]
Image: Reconstructed orbits for the Chelyabinsk meteoroid - the solid blue line represents the median orbit as reconstructed by the NOVAS software. Credit: Zuluaga and Ferrin