The Chelyabinsk meteor may have snuck up on us by surprise, but it didn't take long for a crack team of astronomers from Colombia to figure out where the damned thing came from and the path it took to get here. By sifting through the copious amounts of video footage available, and after performing some clever trigonometry, the team successfully traced the meteor back to the Apollo class of asteroids — an indication that the meteor likely originated from our solar system's asteroid belt.
The Apollo asteroids are a well-known group of near-Earth objects (NEOs) that regularly cross our orbit. They're part of a broader classification of NEOs that include the Atira, Aten, and Amor groupings. All of these NEOs are asteroids with a perihelion distance less than 1.3 AU (a perihelion point is the closest distance an orbiting object has to the Sun). Apollos, which are named after asteroid 1862 Apollo, have a perihelion distance around 1.017 AU, and a semi-major axis larger than Earth's. Of the 9,700 NEOs discovered so far, about 54% of them are Apollos.
The astronomers reached this conclusion after calculating the Chelyabinsk meteor's trajectory, which showed an elliptical, low inclination orbit. This would suggest that it came from within our solar system, most likely from the asteroid belt between Mars and Jupiter.
To make their calculation, Jorge Zuluaga and Ignacio Ferrin, from the University of Antioquia in Medellin, isolated six different variables offered by the video footage. After analyzing the videos, the team settled on what they believed were the two most reliable views, a camera positioned at Revolution Square in Chelyabinsk, and a video recorded in the nearby city of Korkino. They also took the location of the hole in the ice in Lake Chebarkul into account.
The astronomers were most interested at observing the point when the meteor became bright enough to cast a noticeable shadow on the ground — an important clue to help with triangulation.
The resulting values — things like speed, height, and position — were then keyed into astronomy software developed by the U.S. Naval Observatory. And to make up for potential uncertainties about the meteor's movement through the atmosphere, they calculated the most probable orbital parameters. The astronomers admit that their findings are preliminary, but that their analysis will continue as new data becomes available.
The paper, which has yet to be published in a peer reviewed journal, is available on arXiv.