In 2013 a small meteoroid, the size of a house, hurtled through Earth’s atmosphere and exploded over the Russian city of Chelyabinsk. The explosion shattered windows, and more than a thousand people were treated for injuries from flying debris. How many similar-sized rocks have orbits that bring them close to Earth? A new study has answered that question using the Dark Energy Camera (DECam) on the Blanco telescope at the Cerro Tololo Inter-American Observatory. The result lends new insights into the nature and origin of small meteoroids.
Near Earth Objects (NEOs) are asteroids or comets whose orbits bring them close to Earth’s orbit. Their close approach makes them a potential Earth-impact hazard capable of causing widespread destruction.
While very large (10 kilometer-sized) impactors can induce mass extinction events like the event that led to the demise of the dinosaurs, much smaller impactors can also wreak havoc. The meteoroid that exploded in Chelyabinsk unleashed a powerful shock wave that destroyed buildings and blew people off their feet. Relatively petite at a ‘mere’ 17 meters in diameter, comparable to the size of a 6-story building, the impactor, when it exploded, released about ten times the energy of the Hiroshima atomic bomb.
A survey for NEOs being carried out with DECam on the 4-m Blanco telescope at the Cerro Tololo Inter-American Observatory has now estimated the number of objects in near-Earth orbit that are similar in size to the Chelyabinsk impactor. Lori Allen, Director of the Kitt Peak National Observatory and the lead investigator on the study, explained, “There are around 3.5 million NEOs larger than 10 meters, a population ten times smaller than inferred in previous studies. About 90% of these NEOs are in the Chelyabinsk size range of 10-20 meters.”
The study, to be published in the Astronomical Journal, is the first to derive, from a single observational data set with no external model assumptions, the size distribution of NEOs from 1 kilometer down to 10 meters. A similar result was obtained in an independent study that analyzed multiple data sets (Tricarico 2017).