Data gathered by U.S. government sensors and released to NASA for use by the science community reveal that these small impact events are frequent and random. A map of these small impact events - known as fireballs or bolides - recently released by NASA shows the frequency and approximate energy released by bolide events detected from 1994 through 2013. It dwarfs a data-base of small impacts based on infra-sound detections released last fall, but it does not contain all fireballs - objects less than a meter in size - that impacted the Earth during this period.
Over this 20-year interval, U.S. Government assets recorded at least 556 bolide events of various energies. On this world map illustration, the size of the orange dots (daytime events) and blue dots (nighttime events) are proportional to the optical radiated energy of the impact event measured in billions of Joules (GJ) of energy. An approximate conversion between the measured optical radiant energy and the total impact energy can be made using an empirical relationship provided by Peter Brown and colleagues in 2002. For example the smallest dot on the map represents 1 billion Joules (1 GJ) of optical radiant energy, or when expressed in terms of a total impact energy the equivalent of about 5 tons of TNT explosives. Likewise, the dots representing 100, 10,000 and 1,000,000 Giga Joules of optical radiant energies correspond to impact energies of about 300 tons, 18,000 tons and one million tons of TNT explosives respectively.
NASA's list of recent fireball and bolide reports is here.
