Impact event

Impact event

Discussion
Ask a question about 'Impact event'
Start a new discussion about 'Impact event'
Answer questions from other users
Full Discussion Forum
 
Encyclopedia
An impact event is the collision
Collision
A collision is an isolated event which two or more moving bodies exert forces on each other for a relatively short time.Although the most common colloquial use of the word "collision" refers to accidents in which two or more objects collide, the scientific use of the word "collision" implies...

 of a large meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

, asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

, comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

, or other celestial object with the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 or another planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

. 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 localised consequences.

Impact events have been a plot and background element in science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

 since knowledge of real impacts became established in the scientific mainstream.

Sizes and frequencies



Small objects frequently collide with the Earth. There is an inverse relationship
Inverse relationship
An inverse or negative relationship is a mathematical relationship in which one variable, say y, decreases as another, say x, increases. For a linear relation, this can be expressed as y = a-bx, where -b is a constant value less than zero and a is a constant...

 between the size of the object and the frequency that such objects hit the earth. The lunar cratering record shows that the frequency of impacts decreases as approximately the cube of the resulting crater's diameter, which is on average proportional to the diameter of the impactor.
Asteroids with a 1 km (0.621372736649807 mi) diameter strike the Earth every 500,000 years on average. Large collisions – with 5 km (3 mi) objects – happen approximately once every ten million years. The last known impact of an object of 10 km (6 mi) or more in diameter was at the Cretaceous–Tertiary extinction event 65 million years ago.

Asteroids with diameters of 5 to 10 m (16.4 to 32.8 ft) enter the Earth's atmosphere approximately once per year, with as much energy as Little Boy
Little Boy
"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon...

, the atomic bomb dropped on Hiroshima, approximately 15 kilotonnes of TNT. These ordinarily explode in the upper atmosphere
Mesosphere
The mesosphere is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere temperature decreases with increasing height. The upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring...

, and most or all of the solids are vaporized
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....

. Objects with diameters over 50 m (164 ft) strike the Earth approximately once every thousand years, producing explosions comparable to the one known to have detonated above Tunguska
Tunguska event
The Tunguska event, or Tunguska blast or Tunguska explosion, was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia, at about 7:14 a.m...

 in 1908. At least one known asteroid with a diameter of over 1 km (0.621372736649807 mi), (29075) 1950 DA
(29075) 1950 DA
-External links:* from JPL /...

, has a possibility of colliding with Earth on March 16, 2880, but the Torino scale
Torino Scale
The Torino Scale is a method for categorizing the impact hazard associated with near-Earth objects such as asteroids and comets.It is intended as a communication tool for astronomers and the public to assess the seriousness of collision predictions, by combining probability statistics and known...

 only works for impact possibilities within 100 years, and thus cannot apply to this asteroid.

Objects with diameters smaller than 10 m (32.8 ft) are called meteoroids (or meteorites if they strike the ground). An estimated 500 meteorites reach the surface each year, but only 5 or 6 of these are typically recovered and made known to scientists.

Geology of Earth-impact events


Earth has gone through periods of abrupt and catastrophic change, some due to the impact of large asteroids and comets on the planet. A few of these impacts may have caused massive climate change and the extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

 of large numbers of plant and animal species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

.

The Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 is widely attributed to a huge impact early in Earth's history
Giant impact hypothesis
The giant impact hypothesis states that the Moon was created out of the debris left over from a collision between the young Earth and a Mars-sized body. The colliding body is sometimes called Theia for the mythical Greek Titan who was the mother of Selene, the goddess of the moon.The giant impact...

. Impact events earlier in the history of Earth
History of Earth
The history of the Earth describes the most important events and fundamental stages in the development of the planet Earth from its formation 4.578 billion years ago to the present day. Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's...

 have been credited with creative as well as destructive events; it has been proposed that impacting comets delivered the Earth's water, and some have suggested that the origins of life may have been influenced by impacting objects by bringing organic chemicals or lifeforms to the Earth's surface, a theory known as exogenesis.

These modified views of the Earth's history did not emerge until relatively recently, chiefly due to a lack of direct observations and the difficulty in recognizing the signs of an Earth impact because of erosion and weathering. Large-scale terrestrial impacts of the sort that produced the Barringer Crater, locally known as Meteor Crater
Meteor Crater
Meteor Crater is a meteorite impact crater located approximately east of Flagstaff, near Winslow in the northern Arizona desert of the United States. Because the US Department of the Interior Division of Names commonly recognizes names of natural features derived from the nearest post office, the...

, northeast of Flagstaff, Arizona, are rare. Instead, it was widely thought that cratering was the result of volcanism
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....

: the Barringer Crater, for example, was ascribed to a prehistoric volcanic explosion (not an unreasonable hypothesis, given that the volcanic San Francisco Peaks
San Francisco Peaks
The San Francisco Peaks are a volcanic mountain range located in north central Arizona, just north of Flagstaff.The highest summit in the range, Humphreys Peak, is the highest point in the state of Arizona at in elevation. The San Francisco Peaks are the remains of an eroded stratovolcano...

 stand only 30 miles (48.3 km) to the west). Similarly, the craters on the surface of the Moon were ascribed to volcanism.

It was not until 1903–1905 that the Barringer Crater was correctly identified as being an impact crater, and it was not until as recently as 1963 that research by Eugene Merle Shoemaker
Eugene Merle Shoemaker
Eugene Merle Shoemaker , American geologist, was one of the founders of the fields of planetary science....

 conclusively proved this hypothesis. The findings of late 20th-century space exploration
Space exploration
Space exploration is the use of space technology to explore outer space. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft....

 and the work of scientists such as Shoemaker demonstrated that impact cratering was by far the most widespread geological process at work on the solar system's solid bodies. Every surveyed solid body in the solar system was found to be cratered, and there was no reason to believe that the Earth had somehow escaped bombardment from space. In the last few decades of the twentieth century, a large number of highly modified impact craters began to be identified. The largest of these include Vredefort Crater
Vredefort crater
Vredefort crater is the largest verified impact crater on Earth. It is located in the Free State Province of South Africa and named after the town of Vredefort, which is situated near its centre. The site is also known as the Vredefort dome or Vredefort impact structure...

, Sudbury Crater, Chicxulub Crater
Chicxulub Crater
The Chicxulub crater is an ancient impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named...

, and Manicouagan Crater
Manicouagan crater
The Manicouagan Crater is one of the oldest known impact craters and is located primarily in Manicouagan Regional County Municipality in the Côte-Nord region of Québec, Canada, about north of the city of Baie-Comeau. Its northernmost part is located in Caniapiscau Regional County Municipality...

. The first observation of a major impact event occurred in 1994: the collision of the comet Shoemaker-Levy 9
Comet Shoemaker-Levy 9
Comet Shoemaker–Levy 9 was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by...

 with Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

; to date, no such events have been observed on Earth.

Based on crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

 formation rates determined from the Earth's closest celestial partner, the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

, astrogeologists have determined that during the last 600 million years, the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 has been struck by 60 objects of a diameter of 5 km (3 mi) or more. The smallest of these impactors would release the equivalent of ten million megatons
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...

 of TNT and leave a crater 95 km (59 mi) across. For comparison, the largest nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...

 ever detonated, the Tsar Bomba
Tsar Bomba
Tsar Bomba is the nickname for the AN602 hydrogen bomb, the most powerful nuclear weapon ever detonated. It was also referred to as Kuz'kina Mat , in this usage meaning "something that has not been seen before"....

, had a yield of 50 megatons.

Besides direct effect of asteroid impacts on a planet's surface topography, global climate and life, recent studies have shown that several consecutive impacts can have effect on the dynamo mechanism at a planet's core responsible for maintaining the magnetic field of the planet, and can eventually shut down the planet's magnetic field.

While numerous impact craters have been confirmed on land or in the shallow seas over continental shelves, no impact craters in the deep ocean have been widely accepted by the scientific community. Impacts of projectiles as large as 1 km in diameter are generally thought to explode before reaching the sea floor, but it is unknown what would happen if a much larger impactor struck the deep ocean. The lack of a crater, however, does not mean that an ocean impact would not have dangerous implications for humanity. Some scholars have argued that an impact event in an ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

 or sea
Sea
A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...

 may create a tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

 (a giant wave), which can cause destruction both at sea and on land along the coast, but this is disputed.

Recent prehistoric impact events


In addition to the extremely large impacts that happen every few tens of millions of years, there are many smaller impacts that occur more frequently but which leave correspondingly smaller traces behind. Due to the strong forces of erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

 at work on Earth, only relatively recent examples of these smaller impacts are known. A few of the more famous or interesting examples are:


  • Barringer Crater in the USA, the first crater to be proven the result of an impact, ~50,000 years old.
  • the Rio Cuarto craters
    Rio Cuarto craters
    The Río Cuarto craters are a group of impact craters located in Córdoba Province, Argentina.-Discovery:In 1990, Captain Ruben Lianza of the Argentine Air Force, an amateur astronomer, provided a report to an astronomy publication that included aerial pictures of a set of odd teardrop-shaped...

     in Argentina, produced by an asteroid striking Earth at a very low angle, ~10,000 years old.
  • the Lonar crater lake
    Lonar crater lake
    Lonar Lake is a saltwater lake at Lonar in Buldana district, Maharashtra, India, which was created by a meteor hitting the Earth during the Pleistocene Epoch. The impact crater thereby formed is the only hypervelocity meteoritic impact crater on basalt rock. A lake that evolved in the resulting...

     in India, which now has a flourishing semi-tropical jungle around it, ~52,000 years old (though a study published in 2010 gives a much greater age).
  • the Henbury craters in Australia (~5,000 years old), and Kaali crater
    Kaali crater
    Kaali is a group of 9 meteorite craters located on the Estonian island of Saaremaa. Formed in the 7th century BC or about 4000 years ago , it is one of the most recent craters created by an impact event and the only known major impact event that has occurred in a populated area.Prior to the 1930s,...

    s in Estonia (~2,700 years old), apparently produced by objects which broke up before impact.


The Clovis comet hypothesis is a theory that an air burst from a large comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

 above or even into the Laurentide Ice Sheet north of the Great Lakes set all of the North American continent ablaze around 12,900 years ago. The theory attempts to explain the extinction of most of the large animals in North America and the demise of the North American stone age Clovis culture
Clovis culture
The Clovis culture is a prehistoric Paleo-Indian culture that first appears 11,500 RCYBP , at the end of the last glacial period, characterized by the manufacture of "Clovis points" and distinctive bone and ivory tools...

 about at the end of the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

 epoch. Proponents claim the existence of a charred carbon-rich layer of soil found at some 50 Clovis-age sites across the continent. It has been criticized for not being consistent with paleoindian population estimates. Impact specialists have studied the claim and concluded that there never was such an impact, in particular because various physical signs of such an impact cannot be found.

More recent prehistoric impacts are theorized by the Holocene Impact Working Group, including Dallas Abbott of Columbia University's Lamont-Doherty Earth Observatory
Lamont-Doherty Earth Observatory
The Lamont–Doherty Earth Observatory is a research unit of Columbia University located on a campus in Palisades, N.Y., north of Manhattan on the Hudson River.- History :...

. This group points to four enormous chevron sediment deposits
Fenambosy Chevron
The Fenambosy Chevron is one of four chevron-shaped land features on the southwest coast of Madagascar, near the tip of Madagascar, 180 metres high and 5 km inland. It is composed mainly of material found on the ocean. Chevrons such as Fenambosy have been hypothesized as providing evidence of...

 at the southern end of Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...

, containing deep-ocean microfossils fused with metals typically formed by cosmic impacts. All of the chevrons point toward a spot in the middle of the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

 corresponding with the newly hypothesized Burckle crater
Burckle Crater
Burckle Crater is a hypothesized undersea crater that has been proposed by the Holocene Impact Working Group. They considered that it likely was formed by a very large scale and relatively recent comet or meteorite impact event...

 proposed to be some 29 km (18 mi) in diameter, or about 25 times larger than Barringer Crater. This group posits that a large asteroid or comet impact c. 2800-3000 BC produced a mega-tsunami at least 180 m (590.6 ft) high, a catastrophic event that would have affected humanity's cradles of civilization
Cradle of Civilization
The cradle of civilization is a term referring to any of the possible locations for the emergence of civilization.It is usually applied to the Ancient Near Eastern Chalcolithic , especially in the Fertile Crescent , but also extended to sites in Armenia, and the Persian Plateau, besides other Asian...

.
The evidence for the proposed crater has been challenged.

Years 533–534 CE ± 2 impact events have been proposed by the dendrochronologist
Dendrochronology
Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree-rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year...

 Mike Baillie
Mike Baillie
Mike Baillie is a Professor Emeritus of Palaeoecology at Queen's University of Belfast, in Northern Ireland. Baillie is a leading expert in dendrochronology, or dating by means of tree-rings...

 as a possible cause of several brief (typically 5-10 year) climatic downturns recorded in ancient tree ring patterns. Bailliel highlights four such events and suggests that these might have been caused by the dust veils thrown up by the impact of cometary debris.

Modern impact events


A Chinese record states that 10,000 people were killed in Shanxi Province in 1490 by a hail of "falling stones"; some astronomers surmise that this may describe the breakup of a large asteroid, although they find the number of deaths implausible.

Kamil Crater
Kamil Crater
The Kamil Crater is a wide and deep meteorite impact crater in the East Uweinat Desert in southwestern New Valley Governorate, Egypt, Only north of the border with the Sudan and above sea level...

, discovered from Google Earth
Google Earth
Google Earth is a virtual globe, map and geographical information program that was originally called EarthViewer 3D, and was created by Keyhole, Inc, a Central Intelligence Agency funded company acquired by Google in 2004 . It maps the Earth by the superimposition of images obtained from satellite...

 image review in Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

, 45 meters in diameter, 10 meters deep is thought to have been formed less than 3,500 years ago in a then-unpopulated region of Western Egypt. It was found February 19, 2009 by V. de Michelle on a Google Earth image of the East Uweinat Desert, Egypt.

The Mahuika crater
Mahuika crater
Mahuika crater is a proposed submarine bolide impact crater, 20 ± 2 km wide and over 153 m deep, on the New Zealand continental shelf named after the Māori god of fire. It was discovered by Dallas Abbott and her colleagues from the Lamont-Doherty Earth Observatory of the Columbia University.Around...

 may have resulted from a modern impact event. The crater is located south of the Snares Islands (120 km (74.6 mi) southwest of Stewart Island) on the southern New Zealand shelf and is approximately 20 kilometres (12.4 mi) wide. Material extracted from Siple Dome ice core melt water indicates that the impact occurred around 1443 A.D.

The Wabar craters
Wabar craters
The Wabar craters are impact craters brought to the attention of Western scholars by an explorer searching for the legendary city of Ubar in Arabia.-1932 Philby:...

 in Arabia may have been created sometime during the past few hundred years.

The most significant recorded impact in recent times was the Tunguska event
Tunguska event
The Tunguska event, or Tunguska blast or Tunguska explosion, was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia, at about 7:14 a.m...

, which occurred in Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...

, Russia, in 1908. This incident involved an explosion that was probably caused by the airburst of an asteroid or comet 5 to 10 km (3.1 to 6.2 mi) above the Earth's surface, felling an estimated 80 million trees over 2150 square kilometre.

The late Eugene Shoemaker of the U.S. Geological Survey
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...

 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
Hiroshima
is the capital of Hiroshima Prefecture, and the largest city in the Chūgoku region of western Honshu, the largest island of Japan. It became best known as the first city in history to be destroyed by a nuclear weapon when the United States Army Air Forces dropped an atomic bomb on it at 8:15 A.M...

 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
Sikhote-Alin Meteorite
Sikhote-Alin is an iron meteorite that fell in 1947 on the Sikhote-Alin Mountains in eastern Siberia. This fall is unique in the history of meteorites. Though large iron meteorite falls had been witnessed previously and fragments recovered, never before in recorded history had a fall of this...

 fall in Primorye
Primorsky Krai
Primorsky Krai , informally known as Primorye , is a federal subject of Russia . Primorsky means "maritime" in Russian, hence the region is sometimes referred to as Maritime Province or Maritime Territory. Its administrative center is in the city of Vladivostok...

, far eastern Russia, in 1947, and the Revelstoke
Revelstoke, British Columbia
Revelstoke is a city in southeastern British Columbia, Canada. It is located east of Vancouver, and west of Calgary, Alberta. The city is situated on the banks of the Columbia River just south of the Revelstoke Dam and near its confluence with the Illecillewaet River...

 fireball of 1965, which occurred over the snows of British Columbia, Canada.

A small number of meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...

 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
Czechoslovakia
Czechoslovakia or Czecho-Slovakia was a sovereign state in Central Europe which existed from October 1918, when it declared its independence from the Austro-Hungarian Empire, until 1992...

 (now the Czech Republic
Czech Republic
The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....

) in 1959. In this case, two cameras used to photograph meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...

s 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
Smithsonian Astrophysical Observatory
The Smithsonian Astrophysical Observatory is a research institute of the Smithsonian Institution headquartered in Cambridge, Massachusetts, where it is joined with the Harvard College Observatory to form the Harvard-Smithsonian Center for Astrophysics .-History:The SAO was founded in 1890 by...

 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
Nakhla meteorite
Nakhla is a famous martian meteorite fallen in Egypt in 1911.-History:It fell to Earth on June 28, 1911, at approximately 09:00, in the Nakhla region of Abu Hommos, Alexandria, Egypt...

, although this report is disputed. The meteorites that struck this area were identified in the 1980s as Martian
Mars meteorite
A martian meteorite is a rock that formed on the planet Mars, was ejected from Mars by the impact of an asteroid or comet, and landed on the Earth. Of over 53000 meteorites that have been found on Earth, 99 are martian...

 in origin.

The first known modern case of a human hit by a space rock occurred on November 30, 1954, in Sylacauga, Alabama
Sylacauga, Alabama
Sylacauga is a city in Talladega County, Alabama, United States. At the 2000 census the population was 12,616.Nicknames for Sylacauga include: "The Marble City," "Buzzard's Roost" and "Sly Town"....

. There a 4 kg (8.8 lb) 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
The Great Daylight 1972 Fireball
The Great Daylight 1972 Fireball was an Earth-grazing meteoroid which passed within of the surface of the Earth at 20:29 UTC on August 10, 1972. It entered the Earth's atmosphere in daylight over Utah, United States and passed northwards leaving the atmosphere over Alberta, Canada...

 was witnessed by many people moving north over the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...

 from the U.S. Southwest to Canada. It was filmed by a tourist at the Grand Teton National Park
Grand Teton National Park
Grand Teton National Park is a United States National Park located in northwestern Wyoming, U.S. The Park consists of approximately and includes the major peaks of the long Teton Range as well as most of the northern sections of the valley known as Jackson Hole. Only south of Yellowstone...

 in Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

 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 km (36 mi) 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.

In 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 km (16 mi), lighting up the night like day. The meteor that produced the fireball was estimated to be about 4.6 m (15.1 ft) in diameter and with a weight of 180 tonnes. This blast was also featured on The Science Channel series Killer Asteroids, with several witness reports from residents in Atlin, British Columbia
Atlin, British Columbia
Atlin is a community in northwestern British Columbia, Canada, located on the eastern shore of Atlin Lake. In addition to continued gold-mining activity, Atlin is a tourist destination for fishing, hiking and Heliskiing. As of 2004, there are 450 permanent residents.The name comes from Áa Tlein,...

.
A meteor was observed striking Reisadalen in Nordreisa
Nordreisa
Nordreisa is a municipality in Troms county, Norway. The administrative centre of the municipality is the village of Storslett.The municipality consists of the valley of Reisadalen, with the Reisa river and deep pine forests, surrounded by mountains and high plateaus. Most people live in...

 municipality in Troms
Troms
or Romsa is a county in North Norway, bordering Finnmark to the northeast and Nordland in the southwest. To the south is Norrbotten Län in Sweden and further southeast is a shorter border with Lapland Province in Finland. To the west is the Norwegian Sea...

 County, Norway, on June 7, 2006. Although initial witness reports stated that the resultant fireball was equivalent to the Hiroshima nuclear explosion
Atomic bombings of Hiroshima and Nagasaki
During the final stages of World War II in 1945, the United States conducted two atomic bombings against the cities of Hiroshima and Nagasaki in Japan, the first on August 6, 1945, and the second on August 9, 1945. These two events are the only use of nuclear weapons in war to date.For six months...

, scientific analysis places the force of the blast at anywhere from 100-500 tonnes TNT equivalent – around 3% of Hiroshima's yield.

On September 15, 2007, a chondritic
Chondrite
Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids...

 meteor crashed
Carancas impact event
The Carancas impact event refers to the fall of the Carancas chondritic meteorite on September 15, 2007, near the village of Carancas in Peru, close to the Bolivian border and Lake Titicaca. The impact created a crater and scorched earth around its location...

 near the village of Carancas in southeastern Peru near Lake Titicaca
Lake Titicaca
Lake Titicaca is a lake located on the border of Peru and Bolivia. It sits 3,811 m above sea level, making it the highest commercially navigable lake in the world...

, 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.

On November 21, 2009, a fireball was sighted in South Africa by police and traffic cameras. The probable meteor may have landed in a remote area on the Botswana border, and likely made little 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 November 21, 2002, edition of the journal Nature, Peter Brown of the University of Western Ontario reported on his study of U.S. early warning satellite records for the proceeding 8 years. He identified 300 flashes caused by 1 to 10 m (3.3 to 32.8 ft) sized meteors in that time period and estimated the rate of Tunguska
Tunguska event
The Tunguska event, or Tunguska blast or Tunguska explosion, was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia, at about 7:14 a.m...

-sized events as once in 400 years. Eugene 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
Comet Shoemaker-Levy 9
Comet Shoemaker–Levy 9 was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by...

 with Jupiter served as a "wake-up call", and astronomers responded by starting programs such as Lincoln Near-Earth Asteroid Research
Lincoln Near-Earth Asteroid Research
The Lincoln Near-Earth Asteroid Research project is a cooperative project between the United States Air Force, NASA, and MIT's Lincoln Laboratory for the systematic discovery and tracking of near-Earth asteroids. LINEAR was responsible for the majority of asteroid detections since 1998 until...

 (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.

In 1998, two comets were observed plunging into the Sun in close succession. The first of these was on June 1 and the second the next day. A video of this, followed by a dramatic ejection of solar gas (supposedly unrelated to the impacts), can be found at the NASA website. Both of these comets evaporated before coming into contact with the surface of the Sun. According to a theory by NASA Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...

 scientist Zdeněk Sekanina, the latest impactor to actually make contact with the Sun was the "supercomet" Howard-Koomen-Michels
Comet Howard-Koomen-Michels
Comet Howard–Koomen–Michels was a large sungrazer that collided with the Sun on August 30, 1979. It is the only comet known to have made contact with the Sun's surface, as most bodies vaporize before impact.- External links :*...

 on August 30, 1979. (See also sungrazer.)

On October 7, 2008, a meteroid labeled 2008 TC3
2008 TC3
thumb|right|300px|Ground path of the meteoroid; red line is the path, terminating where it would have hit the ground; green line is the infrasound detection of the explosion; orange crosshairs show METEOSAT IR fireball location; predicted altitudes are listed; exact path and fireball altitude not...

 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
Nubian Desert
The Nubian Desert is in the eastern region of the Sahara Desert, spanning approximately 400,000 km² of northeastern Sudan between the Nile and the Red Sea. The arid region, a largely sandstone plateau, has lots of wadis flowing towards the Nile. There is virtually no rainfall in the Nubian,...

.

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.
Between January and May 2010, Hubble
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

's Wide Field Camera 3 took images of an unusual X shape originated in the aftermath of the collision between asteroid P/2010 A2 with a smaller asteroid.

Mass extinctions and impacts


In the past 540 million years there have been five generally-accepted, major mass extinctions that on average extinguished half of all species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

. One of the largest mass extinction to have affected life on Earth
Life on Earth
Life on Earth: A Natural History by David Attenborough is a television natural history series made by the BBC in association with Warner Bros. and Reiner Moritz Productions...

 was in the Permian-Triassic
Permian-Triassic extinction event
The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...

, which ended the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 period 250 million years ago and killed off 90% of all species; life on Earth took 30 million years to recover. The cause of the Permian-Triassic extinction is still matter of debate with the age and origin of proposed impact craters, i.e. the Bedout
Bedout
Bedout , or more specifically the Bedout High, is a geological and geophysical feature centered about 250 km off the northwestern coast of Australia in the Canning and overlying Roebuck basins. Although not obvious from sea floor topography, it is a roughly circular area about 30 km in...

 High structure, hypothesized to be associated with it are still controversial. The last such mass extinction led to the demise of the dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s and coincided with a large meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

 impact; this is the Cretaceous–Tertiary extinction event (also known as the K–T extinction event); This occurred 65 million years ago. There is no definitive evidence of impacts leading to the three other major mass extinctions.

In 1980, physicist Luis Alvarez
Luis Alvarez
Luis W. Alvarez was an American experimental physicist and inventor, who spent nearly all of his long professional career on the faculty of the University of California, Berkeley...

; his son, geologist Walter Alvarez
Walter Alvarez
Walter Alvarez is a professor in the Earth and Planetary Science department at the University of California, Berkeley. He is most widely known for the theory that dinosaurs were killed by an asteroid impact, developed in collaboration with his father, Nobel Prize winning physicist Luis...

; and nuclear chemists Frank Asaro and Helen V. Michael from the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...

 discovered unusually high concentrations of iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...

 in a specific layer of rock strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

 in the Earth's crust. Iridium is an element that is rare on Earth but relatively abundant in many meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

s. From the amount and distribution of iridium present in the 65-million-year-old "iridium layer", the Alvarez team later estimated that an asteroid of 10 to 14 km (6.2 to 8.7 mi) must have collided with the earth. This iridium layer at the K–T boundary
K–T boundary
The K–T boundary is a geological signature, usually a thin band, dated to 65.5 ± 0.3 Ma ago. K is the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period...

 has been found worldwide at 100 different sites. Multidirectionally shocked quartz
Shocked quartz
Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure , the crystalline structure of quartz will be deformed along planes inside the crystal...

 (coesite), which is only known to form as the result of large impacts or atomic bomb explosions, has also been found in the same layer at more than 30 sites. Soot
Soot
Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres,...

 and ash at levels tens of thousands times normal levels were found with the above.

Anomalies in chromium isotopic ratios found within the K-T boundary layer strongly support the impact theory. Chromium isotopic ratios are homogeneous within the earth, therefore these isotopic anomalies exclude a volcanic origin which was also proposed as a cause for the iridium enrichment. Furthermore the chromium isotopic ratios measured in the K-T boundary are similar to the chromium isotopic ratios found in carbonaceous chondrite
Carbonaceous chondrite
Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 7 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites...

s. Thus a probable candidate for the impactor is a carbonaceous asteroid but also a comet is possible because comets are assumed to consist of material similar to carbonaceous chondrites.

Probably the most convincing evidence for a worldwide catastrophe was the discovery of the crater which has since been named Chicxulub Crater
Chicxulub Crater
The Chicxulub crater is an ancient impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named...

. This crater is centered on the Yucatán Peninsula of Mexico and was discovered by Tony Camargo and Glen Pentfield while working as geophysicists for the Mexican oil company PEMEX
Pemex
Petróleos Mexicanos or Pemex is a Mexican state-owned petroleum company. As of 2010, with a total asset worth of $415.75 billion, it is the second non-publicly listed largest company in the world by total market value, and Latin America's second largest enterprise by annual revenue as of 2009...

. What they reported as a circular feature later turned out to be a crater estimated to be 180 km (111.8 mi) in diameter. Other researchers would later find that the end-Cretaceous extinction event that wiped out the dinosaurs had lasted for thousands of years instead of millions of years as had previously been thought. This convinced the vast majority of scientists that this extinction resulted from a point event that is most probably an extraterrestrial impact and not from increased volcanism and climate change (which would spread its main effect over a much longer time period).

Recently, several proposed craters around the world have been dated to approximately the same age as Chicxulub — for example, the Silverpit crater
Silverpit crater
Silverpit crater is a buried sub-sea structure under the North Sea off the coast of the United Kingdom. The crater-like form, named after the Silver Pit — a nearby sea-floor valley recognized by generations of fishermen — was discovered during the routine analysis of seismic data collected during...

 in the United Kingdom, the Boltysh crater
Boltysh crater
The Boltysh Crater is an impact crater in the Kirovohrad Oblast province of Ukraine. The crater is in diameter and its age of 65.17 ± 0.64 million years, based on argon dating techniques, is within error of that of Chicxulub Crater in Mexico, and the K–T boundary...

 in Ukraine and the Shiva crater
Shiva crater
The Shiva crater is a sea floor structure located beneath the Indian Ocean, west of Mumbai, India. It was named by the paleontologist Sankar Chatterjee after Shiva, the Hindu god of destruction and renewal....

 near India. This has led to the suggestion that the Chicxulub impact was one of several that occurred almost simultaneously, perhaps due to a disrupted comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

 impacting the Earth in a similar manner to the collision of Comet Shoemaker-Levy 9
Comet Shoemaker-Levy 9
Comet Shoemaker–Levy 9 was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by...

 with Jupiter in 1994.

It was the lack of high concentrations of iridium and shocked quartz which has prevented the acceptance of the idea that the Permian extinction was also caused by an impact. During the late Permian all the continents were combined into one supercontinent named Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....

 and all the oceans formed one superocean, Panthalassa
Panthalassa
Panthalassa , also known as the Panthalassic Ocean, was the vast global ocean that surrounded the supercontinent Pangaea, during the late Paleozoic and the early Mesozoic years. It included the Pacific Ocean to the west and north and the Tethys Ocean to the southeast...

. If an impact occurred in the ocean and not on land at all, then there would be little shocked quartz released (since oceanic crust has relatively little silica) and much less material.

Although there is now general agreement that there was a huge impact at the end of the Cretaceous that led to the iridium enrichment of the K-T boundary layer, remnants have been found of other impacts of the same order of magnitude that did not result in any mass extinctions, and there is no clear linkage between an impact and any other incident of mass extinction. Nonetheless it is now widely believed that mass extinctions due to impacts are an occasional event in the history of Earth
History of Earth
The history of the Earth describes the most important events and fundamental stages in the development of the planet Earth from its formation 4.578 billion years ago to the present day. Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's...

.

Paleontologists David M. Raup
David M. Raup
David M. Raup is a University of Chicago paleontologist. Raup studied the fossil record and the diversity of life on Earth. Raup contributed to the knowledge of extinction events along with his colleague Jack Sepkoski...

 and Jack Sepkoski
Jack Sepkoski
J. John Sepkoski Jr., , was a University of Chicago paleontologist. Sepkoski studied the fossil record and the diversity of life on Earth. Sepkoski and David Raup contributed to the knowledge of extinction events...

 have proposed that an extinction occurs roughly every 26 million years (though many are relatively minor). This led physicist Richard A. Muller
Richard A. Muller
Richard A. Muller is a noted American professor of physics at the University of California, Berkeley. He is also a faculty senior scientist at the Lawrence Berkeley National Laboratory.-Career:...

 to suggest that these extinctions could be due to a hypothetical companion star to the Sun called Nemesis
Nemesis (star)
Nemesis is a hypothetical hard-to-detect red dwarf star, white dwarf star or brown dwarf, originally postulated in 1984 to be orbiting the Sun at a distance of about 95,000 AU , somewhat beyond the Oort cloud, to explain a perceived cycle of mass extinctions in the geological record, which seem to...

 periodically disrupting the orbits of comets in the Oort cloud
Oort cloud
The Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...

, and leading to a large increase in the number of comets reaching the inner solar system where they might hit Earth.

Indeed, in the early history of the Earth (about four billion years ago) bolide impacts were almost certainly common since the solar system contained far more discrete bodies than at present. Such impacts could have included strikes by asteroids hundreds of kilometers in diameter, with explosions so powerful that they vaporized all the Earth's oceans. It was not until this heavy bombardment slackened that life appears to have begun to evolve on Earth. If such an impact were to occur on Earth today, it is an almost certainty that human civilization would be wiped out. Fortunately, our solar system is much less populated with large objects today and the probability of such an event happening is essentially zero, as the larger asteroids in the asteroid belt and the giant comets in the Kuiper belt that are in this size range are in stable orbits that will not enter the inner solar system, let alone intersect the orbit of Earth, with no observed exceptions.

The leading theory of the Moon's origin is the giant impact theory, which states that Earth was once hit by a planetoid the size of Mars; if this theory holds then that impact was almost certainly the largest hit Earth ever suffered. Peculiarities in the rotation and inclination of the planets, such as Venus' retrograde rotation and the extreme tilt of Uranus' axis, are thought to be the consequence of other such giant impacts, as the current hypotheses of solar system and planetary formation, in absence of impact, could not account for the large transfers of momentum that we clearly see evidence for today, in Venus and Uranus for example.

End of 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
Doomsday event
A doomsday event is a specific, plausibly verifiable or hypothetical occurrence which has an exceptionally destructive effect on the human race...

 with impact event listed as the No. 1 most likely to occur. Until the 1980s this idea was not taken seriously, but opinions changed following the discovery of the Chicxulub Crater
Chicxulub Crater
The Chicxulub crater is an ancient impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named...

, which was further reinforced by witness to the Comet Shoemaker-Levy 9
Comet Shoemaker-Levy 9
Comet Shoemaker–Levy 9 was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by...

 event.

Social attitudes


A joint Pew Research Center
Pew Research Center
The Pew Research Center is an American think tank organization based in Washington, D.C. that provides information on issues, attitudes and trends shaping the United States and the world. The Center and its projects receive funding from The Pew Charitable Trusts. In 1990, Donald S...

/Smithsonian survey from April 21–26, 2010 found that 31% of Americans believed that an asteroid will collide with earth by 2050. A 61% majority disagreed.

Science fiction novels


Numerous science fiction stories and novels center around an impact event; possibly the best-selling was the novel Lucifer's Hammer
Lucifer's Hammer
Lucifer's Hammer is a post-apocalyptic science fiction novel by Larry Niven and Jerry Pournelle, first published in 1977. It was nominated for the Hugo Award for Best Novel in 1978. A comic book adaptation was published by Innovation Comics in 1993....

by Larry Niven
Larry Niven
Laurence van Cott Niven / ˈlæri ˈnɪvən/ is an American science fiction author. His best-known work is Ringworld , which received Hugo, Locus, Ditmar, and Nebula awards. His work is primarily hard science fiction, using big science concepts and theoretical physics...

 and Jerry Pournelle
Jerry Pournelle
Jerry Eugene Pournelle is an American science fiction writer, essayist and journalist who contributed for many years to the computer magazine Byte and has since 1998 been maintaining his own website/blog....

. Arthur C. Clarke
Arthur C. Clarke
Sir Arthur Charles Clarke, CBE, FRAS was a British science fiction author, inventor, and futurist, famous for his short stories and novels, among them 2001: A Space Odyssey, and as a host and commentator in the British television series Mysterious World. For many years, Robert A. Heinlein,...

's novel Rendezvous with Rama
Rendezvous with Rama
Rendezvous with Rama is a novel by Arthur C. Clarke first published in 1972. Set in the 22nd century, the story involves a cylindrical alien starship that enters Earth's solar system...

opens with a significant asteroid impact in northern Italy in the year 2077 which gives rise to the Spaceguard Project, which later discovers the Rama spacecraft. In 1992 a Congressional study in the U.S. led to NASA being directed to undertake a Spaceguard
Spaceguard
The term Spaceguard loosely refers to a number of efforts to discover and study near-Earth objects . Asteroids are discovered by telescopes which repeatedly survey large areas of sky. Efforts which concentrate on discovering NEOs are considered part of the "Spaceguard Survey," regardless of which...

 Survey
with the novel being named as the inspiration for the name to search for Earth-impacting asteroids. This in turn inspired Clarke's 1993 novel The Hammer of God
The Hammer of God
The Hammer of God is a science fiction novel by Arthur C. Clarke originally published in 1993. It deals with an asteroid named Kali headed toward Earth. Captain Robert Singh of the spacecraft Goliath is sent to deflect it. Kali is discovered by Dr...

. A variation on the traditional impact story was provided by Jack McDevitt
Jack McDevitt
Jack McDevitt is an American science fiction author whose novels frequently deal with attempts to make contact with alien races, and with archaeology or xenoarchaeology....

's 1999 novel Moonfall, in which a very large comet travelling at interstellar velocities collides with and partially destroys the Moon, fragments of which then collide with the Earth. The 1985 Niven and Pournelle novel Footfall
Footfall
Footfall is a 1985 science fiction novel written by Larry Niven and Jerry Pournelle. It was nominated for the both the Hugo and Locus Awards in 1986, and was a No...

features the examination of the effects of planetary warfare conducted by an alien species that culminates in the use of asteroids to bombard the planet, creating very large craters and the species' near extinction. Jules Verne contributed a story of planetary impact in "Off on a Comet". In "The Moon is a Harsh Mistress", Robert A. Heinlein
Robert A. Heinlein
Robert Anson Heinlein was an American science fiction writer. Often called the "dean of science fiction writers", he was one of the most influential and controversial authors of the genre. He set a standard for science and engineering plausibility and helped to raise the genre's standards of...

 had the moon rebels use rock filled shipping containers as a weapon against their Earthside oppressors.

Similarly in the science fiction television series Babylon 5 war between the Narn and Centauri is brought to a swift end when the Centauri use "Mass Drivers" a weapon system that propels asteroids at the suface of the Narn homeworld causing severe ecological damage.

Cinema


Several disaster film
Disaster film
A disaster film is a film genre that has an impending or ongoing disaster as its subject...

s have also been made: released during the turbulence of World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

, the Danish feature film The End of the World revolves around the near-miss of a comet which causes fire showers and social unrest in Europe. When Worlds Collide
When Worlds Collide (film)
When Worlds Collide is a 1951 science fiction film based on the 1933 novel co-written by Philip Gordon Wylie and Edwin Balmer. The film was shot in Technicolor, directed by Rudolph Maté and was the winner of the 1951 Academy Award for special effects....

(1951) based on a 1933 novel by Philip Wylie, deals with two planets on a collision course with Earth – the smaller planet a "near miss," causing extensive damage and destruction, followed by a direct hit from the larger planet. Meteor
Meteor (film)
Meteor is a 1979 science fiction Technicolor disaster film in which scientists detect an asteroid on a collision course with Earth and struggle with international, cold war politics in their efforts to prevent disaster. The movie starred Sean Connery and Natalie Wood.It was directed by Ronald Neame...

(1979) features small asteroid fragments and a large 8 km (5 mi) wide asteroid heading for Earth. Orbiting U.S. and Soviet nuclear weapons platforms are turned away from their respective earthbound targets, and toward the incoming threat. In 1998, two films were released in the United States on the subject of attempting to stop impact events: Touchstone Pictures' Armageddon, about an asteroid; and Paramount/DreamWorks' Deep Impact
Deep Impact (film)
Deep Impact is a 1998 science-fiction disaster-drama film released by Paramount Pictures and DreamWorks in the United States on May 8, 1998. The film was directed by Mimi Leder and stars Robert Duvall, Elijah Wood, Téa Leoni, and Morgan Freeman...

, about a comet. Both involved using Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

-derived craft to deliver large amounts of nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...

s to destroy their targets. The 2008 American Broadcasting Company's miniseries
Miniseries
A miniseries , in a serial storytelling medium, is a television show production which tells a story in a limited number of episodes. The exact number is open to interpretation; however, they are usually limited to fewer than a whole season. The term "miniseries" is generally a North American term...

 Impact
Impact (TV miniseries)
Impact is a mini-series about a meteor shower which eventually sends the moon on a collision course with Earth. The two-part mini-series premiered February 14 and 15, 2009 on the Canadian premium television channel Super Channel and was also shown on ABC on June 21 and 28, 2009 and on Alpha TV on...

deals about a splinter of a brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...

 hidden in a meteor shower which strikes the Moon and sends it on a collision course with Earth. The 2011 film Melancholia uses the motif of an impact event incorporated in the aesthetics of romanticism
Romanticism
Romanticism was an artistic, literary and intellectual movement that originated in the second half of the 18th century in Europe, and gained strength in reaction to the Industrial Revolution...

.

See also

  • 2012 phenomenon
    2012 phenomenon
    The 2012 phenomenon comprises a range of eschatological beliefs that cataclysmic or transformative events will occur on December 21, 2012. This date is regarded as the end-date of a 5,125-year-long cycle in the Mesoamerican Long Count calendar...

  • Asteroid capture
    Asteroid capture
    Asteroid capture can happen when an asteroid approaches a large planetary body.Typically asteroids that approach close enough to a planet are thrown out into space or impact the body. In rarer instances, the asteroid is captured in orbit around the planet...

  • Asteroid deflection strategies
    Asteroid deflection strategies
    Asteroid mitigation strategies are "planetary defense" methods by which near-Earth objects could be diverted, preventing potentially catastrophic impact events. A sufficiently large impact would cause massive tsunamis or an impact winter, or both...

  • B612 Foundation
    B612 Foundation
    The B612 Foundation is a private foundation dedicated to protecting the Earth from asteroid strikes. Their immediate goal is to "significantly alter the orbit of an asteroid in a controlled manner by 2015"....

  • Earth Impact Database
    Earth Impact Database
    The Earth Impact Database is the authoritative source for information on confirmed impact structures or craters on Earth. It was initiated in 1955 by the Dominion Observatory, Ottawa, under the direction of Dr. Carlyle S. Beals...

  • Extinction event
    Extinction event
    An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...

  • Impact crater
    Impact crater
    In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

  • Impact gardening
    Impact gardening
    Impact gardening is the process by which impact events stir the outermost crusts of moons and other celestial objects with no atmospheres. In the particular case of the Moon, this is more often known as lunar gardening...

  • Near-Earth asteroids
  • Near-Earth objects
  • Pan-STARRS
    Pan-STARRS
    The Panoramic Survey Telescope and Rapid Response System is a planned array of astronomical cameras and telescopes and computing facility that will survey the sky on a continual basis, including accurate astrometry and photometry of detected objects...

  • Potentially hazardous asteroid
  • Spaceguard
    Spaceguard
    The term Spaceguard loosely refers to a number of efforts to discover and study near-Earth objects . Asteroids are discovered by telescopes which repeatedly survey large areas of sky. Efforts which concentrate on discovering NEOs are considered part of the "Spaceguard Survey," regardless of which...

  • Torino scale
    Torino Scale
    The Torino Scale is a method for categorizing the impact hazard associated with near-Earth objects such as asteroids and comets.It is intended as a communication tool for astronomers and the public to assess the seriousness of collision predictions, by combining probability statistics and known...

    , 0 to 10
  • Palermo scale
  • Crust tsunami
    Crust tsunami
    A crust tsunami is a solid-ground analog of a tsunami where the Earth's crust becomes detached from the mantle following the impact of a massive asteroid or comet.A simulation of such as event is shown in Miracle Planet: The Violent Past....


External links