Meteor Strikes & Asteroid Near Misses

At 09:20 local time on February 15, 2013, a meteor streaked into earth’s atmosphere over Siberia’s Ural Mountains and exploded in a fireball with the released energy of 500 kilotons of TNT, 20 to 30 times more powerful than the Hiroshima atomic bomb . The meteor exploded 15 miles (25km) above ground. The shock wave from the air burst damaged 3,000 buildings and injured 1,500 people, mainly from flying glass.

Moving at 40,000 mph (18km/s), the meteor measured 56 ft (17m) across, and weighed an estimated 10 tons before breaking apart in the blast. It is the largest object to have entered earth’s atmosphere since 1908, and the only known event of this kind to result in mass injuries. In 1908, the Tunguska meteor exploded in a fireball over an unpopulated area of Siberia, flattening trees 10 mi (16km) in all directions, and causing a magnitude 5.0 earthquake.

16 hours after the February 15th meteor strike, earth had a close encounter with a 44,000-ton asteroid measuring 148 ft (45m) in diameter. This space rock passed 17,200 mi (27,700km) above earth’s equator, but below several communications satellites orbiting at higher altitudes. An asteroid of this size colliding with earth would result in great environmental damage wherever it hit, and in serious loss of life if it struck a populated area.  Astronomers say there was no connection between the two events, since they arrived from different directions at different times.

Bodies from outer space have hit earth in the past, causing widespread destruction. The prime example is the asteroid 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.

NASA has placed a high priority on early detection of approaching asteroids  NASA’s Wide-field Infrared Survey Explorer (WISE), an earth-orbiting infrared telescope operated by JPL, makes the possibility of an undetected killer asteroid striking earth less likely. The WISE observatory is designed to find, track, and analyze Potentially Hazardous Asteroids (PHAs), asteroids with diameters larger than 330 ft (100m). 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 most dangerous PHAs are those with diameters exceeding 3,300 ft (1km). Out of an existing total of 981 of these largest asteroids, 911 (93%) 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.

NASA is funding the development of another asteroid detection system called ATLAS, an array of small telescopes with wide fields of view scanning the entire sky several times a night. It is intended to pick up smaller asteroids the size of the meteor that struck Russia, and establish the exact time and position of impact 24 hours ahead, giving local populations time to prepare.

If WISE were to detect a giant asteroid on collision course with earth, is there a way to deflect it before it arrives? No tested deflection system is available today, but several are in the planning stage. One is a gravitational tractor, a large ion-driven spacecraft that would hover near the asteroid, using its ion thrusters to create gravity tug that would gradually alter the asteroid’s course away from earth.

Another proposed system is called DE-STAR (directed energy orbital defense system). This device harnesses the power of the sun and coverts it into a massive array of laser beams that can deflect or even destroy asteroids threatening earth. It is not a science fiction idea, according to the two UC Santa Barbara physicists developing the system, since all the components are presently available. Scaling up to the size needed would be the challenge.