Recent Asteroid impacts on Earth and the prediction of the end of the world – the doomsday!

Small objects frequently collide with the Earth. There is an inverse relationship between the size of the object and the frequency that such objects hit the earth. Asteroids with a 1 km diameter strike the Earth every 500,000 years on average. Large collisions—with five kilometer objects—happen approximately once every ten million years. The last known impact of an object of 10 km or more in diameter was at the Cretaceous-Tertiary extinction event 65 million years ago. Asteroids with diameters of 5-10 m enter the Earth’s atmosphere approximately once per year, with as much energy as Little Boy, the atomic bomb dropped on Hiroshima, approximately 15 kiloton’s of TNT. These ordinarily explode in the upper atmosphere, and most or all of the solids are vaporized. Objects of diameters of over 50 meters strike the Earth approximately once every thousand years, producing explosions comparable to the one observed at Tunguska in 1908. At least one known asteroid with a diameter of over 1 km, (29075) 1950 DA, has a calculated probability of colliding with Earth in March 2880, with a Torino scale rating of two.

Throughout recorded history, hundreds of minor impact events (and exploding bolides) have been reported, with some occurrences causing deaths, injuries, property damage, or other significant localized consequences.

In China’s Shanxi Province, 10,000 people were said to have been killed in 1490 by a hail of “falling stones” that some astronomers surmise may have been triggered by the breakup of a large asteroid.

The most significant recorded impact in recent times was the Tunguska event, which occurred in Siberia, Russia, in 1908. This incident involved an explosion that was probably caused by the airburst of an asteroid or comet 5 to 10 kilometers (3–6 mi) above the Earth’s surface, felling an estimated 80 million trees over 2,150 square kilometers (830 sq mi).

The late Eugene Shoemaker of the U.S. Geological Survey came up with an estimate of the rate of Earth impacts, and suggested that an event about the size of the nuclear weapon that destroyed Hiroshima occurs about once a year. Such events would seem to be spectacularly obvious, but they generally go unnoticed for a number of reasons: the majority of the Earth’s surface is covered by water; a good portion of the land surface is uninhabited; and the explosions generally occur at relatively high altitude, resulting in a huge flash and thunderclap but no real damage.

Some have been observed. Noteworthy examples include the Sikhote-Alin Meteorite fall in Primorye, far eastern Russia, in 1947, and the Revelstoke fireball of 1965, which occurred over the snows of British Columbia, Canada.

A small number of meteorite falls have been observed with automated cameras and recovered following calculation of the impact point. The first of these was the Pribram meteorite, which fell in Czechoslovakia (now the Czech Republic) in 1959. In this case, two cameras used to photograph meteors captured images of the fireball. The images were used both to determine the location of the stones on the ground and, more significantly, to calculate for the first time an accurate orbit for a recovered meteorite.

Following the Pribram fall, other nations established automated observing programs aimed at studying infalling meteorites. One of these was the Prairie Network, operated by the Smithsonian Astrophysical Observatory from 1963 to 1975 in the midwestern US. This program also observed a meteorite fall, the Lost City chondrite, allowing its recovery and a calculation of its orbit. Another program in Canada, the Meteorite Observation and Recovery Project, ran from 1971 to 1985. It too recovered a single meteorite, Innisfree, in 1977. Finally, observations by the European Fireball Network, a descendant of the original Czech program that recovered Pribram, led to the discovery and orbit calculations for the Neuschwanstein meteorite in 2002.

The only reported fatality from meteorite impacts is an Egyptian dog that was killed in 1911 by the Nakhla meteorite, although this report is disputed. The meteorites that struck this area were identified in the 1980s as Martian in origin.

The first known modern case of a human hit by a space rock occurred on November 30, 1954 in Sylacauga, Alabama. There a 4 kg stone chondrite crashed through a roof and hit Ann Hodges in her living room after it bounced off her radio. She was badly bruised. Several persons have since claimed to have been struck by ‘meteorites’ but no verifiable meteorites have resulted.

On August 10, 1972, a meteor which became known as The Great Daylight 1972 Fireball was witnessed by many people moving north over the Rocky Mountains from the U.S. Southwest to Canada. It was filmed by a tourist at the Grand Teton National Park in Wyoming with an 8-millimeter color movie camera. The object was in the range of size from a car to a house and could have ended its life in a Hiroshima-sized blast, but there was never any explosion. Analysis of the trajectory indicated that it never came much lower than 58 kilometers off the ground, and the conclusion was that it had grazed Earth’s atmosphere for about 100 seconds, then skipped back out of the atmosphere to return to its orbit around the Sun.

On the dark morning hours of January 18, 2000, a fireball exploded over the city of Whitehorse in the Canadian Yukon at an altitude of about 26 kilometers, lighting up the night like day. The meteor that produced the fireball was estimated to be about 4.6 meters in diameter and with a weight of 180 tones. This blast was also featured on the Science Channel series Killer Asteroids, with several witness reports from residents in Atlin, British Columbia.

A meteor was observed striking Reisadalen in Nordreisa municipality in Troms County, Norway, on June 7, 2006. Although initial witness reports stated that the resultant fireball was equivalent to the Hiroshima nuclear explosion, scientific analysis places the force of the blast at anywhere from 100-500 tons TNT equivalent—at most, around 3% of Hiroshima’s yield.

On September 15, 2007, a chondritic meteor crashed near the village of Carancas in southeastern Peru near Lake Titicaca, leaving a water-filled hole and spewing gases across the surrounding area. Many residents became ill, apparently from the noxious gases shortly after the impact.

Many impact events occur without being observed by anyone on the ground. Between 1975 and 1992, American missile early warning satellites picked up 136 major explosions in the upper atmosphere. In the 21-Nov-2002 edition of the Journal Nature, Peter Brown of the University of Western Ontario reported on his study of US early warning satellite records for the proceeding 8 years. He identified 300 flashes caused by 1 m to 10 m sized meteors in that time period and estimated the rate of Tunguska sized events as once in 400 years. Shoemaker estimated that one of such magnitude occurs about once every 300 years, though more recent analyses have suggested he exaggerated by an order of magnitude.

The 1994 impact of Comet Shoemaker-Levy 9 with Jupiter also served as a “wake-up call”, and astronomers responded by starting programs such as Lincoln Near-Earth Asteroid Research (LINEAR), Near-Earth Asteroid Tracking (NEAT), Lowell Observatory Near-Earth Object Search (LONEOS) and several others which have drastically increased the rate of asteroid discovery. However, many objects undoubtedly still remain undetected.

On October 7, 2008, a meteroid labeled 2008 TC3 was tracked for 20 hours as it approached Earth and as it fell through the atmosphere and impacted in Sudan. This was the first time an object was detected before it reached the atmosphere and hundreds of pieces of the meteorite were recovered from the Nubian Desert.

Close encounters and forecasts of new asteroid impacts on earth

On July 19, 2009, a new black spot about the size of Earth was discovered in Jupiter’s southern hemisphere by an amateur astronomer. Thermal infrared analysis showed it was warm and spectroscopic methods detected ammonia. JPL scientists confirmed that another impact event on Jupiter had occurred, probably a small undiscovered comet or other icy body.

On March 31, 2004, a 6 m meteoroid, 2004 FU162 made the second closest approach on record with a separation of only 6,500 km. Because this object is certainly too small to pass through the atmosphere, it is classed as a meteoroid rather than an asteroid.

In 2004, a newly discovered 320 m asteroid, 99942 Apophis (previously called 2004 MN4), achieved the highest impact probability of any potentially dangerous object. The probability of collision on April 13, 2029 is estimated to be as high as 1 in 17 by Steve Chesley of NASA’s Jet Propulsion Laboratory, though the previously published figure was the slightly lower odds of 1 in 37, calculated in December 2004. Later observations showed that the asteroid will miss the earth by 25,600 km (within the orbits of communications satellites) in 2029, but its orbit will be altered unpredictably in a way which does not rule out a collision on April 13 or 14, 2036 or later in the century. These possible future dates have a cumulative probability of 1 in 45,000 for an impact in the 21st century.

Asteroid 2004 VD17, of 580 m, previously was estimated to have a probability of 1 in 63,000 of striking earth on May 4, 2102 (as of July 2006), with risk 1 on the Torino scale, but further observations lowered the estimate. As of the observation on December 17, 2006, JPL assigns 2004 VD17 a Torino value of 0 and an impact probability of 1 in 41.667 million in the next 100 years.

Asteroid (29075) 1950 DA has a potential to collide with Earth on March 16, 2880. The probability of impact is either 1 in 300 or zero, depending on which one of the two possible directions for the asteroid’s spin pole is correct. This asteroid has a mean diameter of about 1.1 km. The energy released by the collision would cause major effects on the climate and biosphere and may be devastating to human civilization.

The latest close encounter to earth.

Asteroid 2007 TU24, with an estimated diameter between 300-500 meters, came very close to earth orbit by 1.4 times the lunar distance on January 29, 2008. The orbit of the asteroid is shown on NASA’s website.

End of the civilization?

An impact event is commonly seen as a scenario that would bring about the end of civilization. In 2000, Discover Magazine published a list of 20 possible sudden doomsday scenarios with impact event listed as the number one most likely to occur. Until the 1980s this idea was not taken seriously, but all that changed after the discovery of the Chicxulub Crater which was further reinforced by witness to the Comet Shoemaker-Levy 9 event. Since then there has been more interest from the scientific community and greater public awareness of the possibility of impact events.