Editorial: Celestial fireball

Published in The Hindu on March 2, 2013

The 2012 DA14 asteroid tracked in advance did not harm us; it skimmed past nearly 27,600 km from the Earth on February 15. But the same day, a meteor, unconnected with 2012 DA14, came out of the blue and exploded over Chelyabinsk, Russia at 9.25 am local time injuring more than a thousand people. It has many firsts to its credit. The 55-foot meteor weighed about 10,000 tonnes before it entered Earth’s atmosphere. It is the largest known celestial object to strike Earth more than a century after the one that came crashing down over the Tunguska River in Siberia in 1908. The Chelyabinsk meteor had a speed of only 18 km per second, far less than the April 22, 2012 Sutter’s Mill record speed of 28.6 km per second. Once the Russian meteor entered the atmosphere, a combination of pressure and heat caused it to break apart 19-24 kilometres above the earth producing a fireball that blazed across the sky. According to the Russian Geographic Society, the bright flare was more than 2,500 degree C. The disintegration took place 32.5 seconds after it entered the atmosphere, and released an estimated energy of nearly 500 kilotons, NASA notes. The shockwaves caused by the explosion shattered glass and damaged many buildings. The infrasound produced by the meteor was the strongest ever detected by the Comprehensive Test Ban Treaty Organisation (CTBT) sensors.

Based on video footage, researchers have already reconstructed the meteor’s orbit and class. According to the February 22 results posted on arXiv, only “a relatively small number” of meteors’ orbits have ever been reconstructed. Results suggest the meteor belongs to the common Apollo family of near-earth asteroids from the belt between Mars and Jupiter. Meteors come crashing into the atmosphere very often, but only a few strike our planet. Yet, the compulsion to spot dangerous ones hurtling towards Earth cannot be overemphasised. However, even under the best of conditions, the faint Russian meteor coming in the morning from the east would have been visible at best just two hours before it struck, notes NASA. Aside from their damage potential, it must be remembered that meteorites have great scientific value; they provide invaluable information about the Solar System’s early history. The three meteorite pieces of Sutter’s Mill carbonaceous chondrites recovered within two days of its disintegration provided “a rare glimpse … of reactive and organic compounds that may be present at the surface of asteroids,” a December 2012 paper in Science notes. Though the meteorite’s pieces are ordinary chondrites with a stony composition, their immediate recovery before possible contamination can spring a surprise or two about the heavenly fireball’s properties.