Small near-Earth asteroids, around a meter in size, hit our atmosphere and disintegrate around every other week. We now know this because “U.S. sensors” can, and do, detect and measure the energy released by these detonations. As this NASA Web story reports, an unidentified source (you figure it out…) has given the agency 20 years worth of data collected by (ahem) “U.S. government sensors” on “bolide impact events.” These data will be (but aren’t quite yet) available to the scientific community for research. What’s a bolide, and what are bolide impact events? See this NASA Web page for information. Also see this story by Leonard David about the “fireball” site, which he said went up March 1, 2013. Back to the “newly released data.” These twenty years worth of observations show that small asteroid impacts with Earth’s atmosphere are “frequent and random.” A map of these small impact events shows the frequency of, and energy released by, impacts detected from 1994 through 2013. “Over this 20-year interval,” NASA says, “U.S. Government assets recorded at least 556 bolide events of various energies.” The sizes of the dots are indicative of the amount of “optical radiated energy” released, measured in billions of Joules (GJ). Orange dots represent daytime events, and blue dots represent nighttime events. As NASA notes, the largest asteroid impact with the atmosphere during this 20-year interval was the so-called Chelyabinsk event, in which a 20-meter object exploded over Russia on February 15, 2013, releasing the energy equivalent of 440,000 – 500,000 tons of TNT. This is a really interesting story, in my biased opinion (I work as a consultant to NASA’s Near Earth Object (NEO) Observations Program). The map is a particularly striking visual depiction of what’s going on over our heads all the time – largely though not completely without consequences, as the blast wave generated by the Chelyabinsk event shattered glass and damaged buildings over a wide area. The map shows that because these impacts are randomly distributed, about three quarters of them occur over oceans and about half occur during daylight hours. I’d guess that many of these events had few to zero “naked eye” human observers. As NASA’s story notes, “Meteor Crater near Winslow, Arizona, is evidence of the impact with Earth’s surface of a 50-meter asteroid about 50,000 years ago.” I visited Meteor Crater in 2013 – quite impressive (see below).
Credit: LA Lewis
I’ll be interested to see what other insights NEO scientists may glean from this rich database. Thanks to “unidentified source” for repurposing these data.