A meteor broke apart over rural Russia on Friday morning, injuring at least 1,200 people. Hours later, an asteroid known as 2012 DA14 passed about 17,000 miles above Earth's surface — a close shave in astronomical terms, passing nearer than many of our communications satellites. One was predicted; the other was not.
These events were unrelated, but they underscore how crucial it is that nations know, quickly, what is falling from the sky and what, if any, dangers are posed.
Every day about 40 tons of space debris hit the atmosphere, burn and settle to Earth, NASA has found. The vast majority of the detritus consists of meteoroids no larger than a grain of sand, but even tiny specks pack a wallop: A typical meteor hits Earth traveling at least seven miles per second, at least 30 times faster than a bullet shot from a handgun. That is why a tiny meteoroid can make such a spectacular shooting star.
According to the Russian Academy of Sciences, the meteor that disintegrated over Siberia on Friday weighed in the neighborhood of 10 tons. It was thought to be traveling at 10 to 12 miles per second when it broke apart.
Every year or so, such a meteor blazes through the sky somewhere over Earth. But every 100 years or so, Earth is hit by a meteor large enough to cause much more significant devastation. Such an impact occurred in 1908 in Tunguska, Russia, when a meteor 100 feet or so in diameter exploded in the Siberian wilderness, releasing about 1,000 times the amount of energy as the nuclear bomb dropped on Hiroshima.
And every 100 million years or so, Earth is hit by a meteor large enough to cause mass extinctions, like the one at the end of the age of dinosaurs. These threats are minuscule on a day-to-day basis, but surely any existential threat to the human race must be taken seriously.