On Feb. 15, 2013, a small asteroid exploded about 40 km to the south of the Russian city of Chelyabinsk. Its proximity to a population center led to many injuries and widespread blast damage, but also yielded a plethora of serendipitous data in the form of video footage from security and dashboard cameras. Combined with seismic, infrasound, and satellite records, this data provides a rich and multi-faceted means to determine the projectile size and entry parameters, and develop a self-consistent model of the airburst.
The best estimate of the kinetic yield (explosive energy) is 400-500 kilotons, making Chelyabinsk the most powerful such event observed since the 1908 Tunguska explosion (3-5 megatons). Analysis of video combined with subsequent on-site stellar calibrations enable precise estimates of entry velocity (19 km/s), angle (17° elevation) and altitude of peak brightness (29 km). This implies a pre-entry diameter of ~ 20 m and mass of ~12,000 tonnes.
Hydrodynamic models can now be initialized with extremely accurate energy depositions at correct locations, and results can be compared to observations (such as timing and distribution of blast energy at the surface, and evolution of the trail) to validate the models and better understand the physical phenomena associated with airbursts. According to observation-based size/frequency curves, Chelyabinsk is approximately a once-per-century event Tunguska is about once-per-millennium. These two outliers suggest that the curves underestimate the frequency of large airbursts. Models suggest that they are more damaging than nuclear explosions of the same yield (traditionally used to estimate impact risk). The risk from airbursts is therefore greater than previously thought.
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000