Meteors on the Mind
November 7, 2013
The sudden appearance of a bright streak in the skies of southern California last night and newly released studies of the meteor that exploded over the Russian city of Chelyabinsk last February are providing unsettling reminders of the threat space rocks pose to Earth. The California fireball, which caused no reported injuries or property damage, was probably part of the annual South Taurid meteor shower, according the weather department of the North American Aerospace Defense Command (NORAD). The Russian meteor, in contrast, is part of a much scarier story reported in three studies in the science journals Nature and Science.
Scientific analysis has revealed that before it exploded, the Chelyabinsk meteor was a 1,900-pound (860-kilogram) asteroid about 65 feet (20 meters) in diameter. It entered the atmosphere at a speed of 43,000 miles (69,200 meters) per hour, breaking up and producing a series of airbursts at an altitude of about 20 miles (32 kilometers). The explosion resulted in about 1,200 injuries–mostly from flying glass from the many windows broken by the resulting shock wave. The light from the fireball was so bright it caused mild cases of sunburns and retinal burns in some people on the ground.
It could have been worse, the scientists pointed out. The Chelyabinsk meteor was basically a pile of rubble loosely held together by veins of metal. It also broke up at a fairly high altitude. A heavier meteor–of the type made of mainly iron and nickel–would have produced a bigger shock wave, especially if it had exploded at a lower altitude. Such a meteor would also have produced more falling debris. (About 76 percent of the meteor apparently burned up in the atmosphere). Unfortunately, the scientists said, the Chelyabinsk meteor likely broke off an even bigger object–which is still out there. Even worse, an analysis of fireballs appearing in Earth’s skies over the past 100 years suggests that meteors the size of the Chelyabinsk meteor may be hitting Earth 10 times as often as scientists had believed.
Scientists with the Near-Earth Object Program, established by NASA and the Jet Propulsion Laboratory in Pasadena, California, are working to identify and track comets and asteroids that move around the sun near Earth’s orbit. The major role of the program is to determine if any near-Earth objects (NEO’s) could strike Earth. But program scientists never saw the Chelyabinsk meteor coming. It was too small to be identified at large distances from Earth. Moreover, it entered Earth’s atmosphere from the direction of the sun and so was lost in glare. Scientists note, however, that no one in recorded human history has ever been killed by an asteroid.
Additional World Book articles:
- Dawn
- Eros
- Vesta
- When Worlds and Comets Collide (a special report)
- What Has Caused Mass Extinctions (a special report)