Bodies from outer space have hit earth in the past, causing widespread destruction. Two examples are the asteroid or comet that struck in the Gulf of Mexico 65 million years ago, creating the massive Chicxulub crater and perhaps leading to the extinction of the dinosaurs. And the fireball that exploded over an unpopulated area of Siberia in 1908, flattening trees 10 miles (16km) in all directions, and causing a magnitude 5.0 earthquake. Computer simulations show that it was a small but dense asteroid that exploded above ground with the power of several hundred atomic bombs. If it had hit a city, the loss of life would have been catastrophic.
Can it happen again? NASA’s Wide-field Infrared Survey Explorer (WISE), an earth-orbiting telescope operated by JPL, makes the possibility of an undetected killer asteroid striking earth far less likely. The WISE observatory is designed to find, track, and analyze Potentially Hazardous Asteroids (PHAs), asteroids in low earth orbit with diameters larger than 330 ft (100m). If they measure 330 ft (100m) up to 3,300 ft (1km), they are considered medium-size asteroids. WISE has already located 4,200 such objects, with an estimated 15,000 still to be pinpointed. NASA’s objective is to eventually complete a survey of all PHAs, their size, composition, trajectory, and degree of threat.
The largest and considered most dangerous PHAs are those with diameters exceeding 3,300 ft (1km). 911 out of an existing total of 981 (93%) of these largest asteroids have been located and analyzed. Some are the size of a small mountain, and if one were to impact our planet the consequences would be devastating. In the past, a PHA – one with a diameter of 330 ft (100m) or more — has struck earth on the average of once every one million years. But now NASA has the ability to zero in on and dispatch robotic spacecraft to any asteroid in earth orbit. It’s possible that a vehicle could land on and apply enough rocket power to the threatening asteroid to move its trajectory away from earth.
When you consider that there have been no recorded human fatalities from meteor or asteroid strikes in modern history, but that more than 1,200,000 die every year in automobile accidents around the world, the asteroid risk factor is exceptionally low compared with driving your car.