title: The trajectory, structure and origin of the Chelyabinsk asteroidal impactor.
abstract: Earth is continuously colliding with fragments of asteroids and comets of various sizes. The largest encounter in historical times occurred over the Tunguska river in Siberia in 1908, producing an airburst of energy equivalent to 5-15 megatons of trinitrotoluene (1 kiloton of trinitrotoluene represents an energy of 4.185 × 10(12) joules). Until recently, the next most energetic airburst events occurred over Indonesia in 2009 and near the Marshall Islands in 1994, both with energies of several tens of kilotons. Here we report an analysis of selected video records of the Chelyabinsk superbolide of 15 February 2013, with energy equivalent to 500 kilotons of trinitrotoluene, and details of its atmospheric passage. We found that its orbit was similar to the orbit of the two-kilometre-diameter asteroid 86039 (1999 NC43), to a degree of statistical significance sufficient to suggest that the two were once part of the same object. The bulk strength--the ability to resist breakage--of the Chelyabinsk asteroid, of about one megapascal, was similar to that of smaller meteoroids and corresponds to a heavily fractured single stone. The asteroid broke into small pieces between the altitudes of 45 and 30 kilometres, preventing more-serious damage on the ground. The total mass of surviving fragments larger than 100 grams was lower than expected.
authors.affiliation: Astronomical Institute, Academy of Sciences of the Czech Republic, CZ-251 65 Ondřejov, Czech Republic.
authors.forename: Jiří
authors.initials: J
authors.lastname: Borovička
authors.forename: Pavel
authors.initials: P
authors.lastname: Spurný
authors.forename: Peter
authors.initials: P
authors.lastname: Brown
authors.forename: Paul
authors.initials: P
authors.lastname: Wiegert
authors.forename: Pavel
authors.initials: P
authors.lastname: Kalenda
authors.forename: David
authors.initials: D
authors.lastname: Clark
authors.forename: Lukáš
authors.initials: L
authors.lastname: Shrbený