Asteroid impact avoidance

"Planetary defense" redirects here. For defending against alien invasion in fiction, see Alien invasion.

Artist's impression of a major impact event. The collision between Earth and an asteroid a few kilometres in diameter releases as much energy as the simultaneous detonation of several million nuclear bombs.

Asteroid impact avoidance comprises a number of methods by which near-Earth objects (NEO) could be diverted, preventing potentially catastrophic impact events. A sufficiently large impact by an asteroid or other NEOs would cause massive tsunamis, continent-wide firestorms, or (by placing large quantities of dust into the stratosphere, blocking sunlight) an impact winter, and even a combination of several apocalyptic events. A collision between the Earth and an approximately 10 kilometre wide object 65 million years ago is believed to have produced the Chicxulub Crater and the Cretaceous–Paleogene extinction event, widely held responsible for the extinction of the dinosaurs.

While the chances of such an event are no greater now than at any other time in history, there is a very high chance that one will happen eventually. Recent astronomical events—such as Shoemaker-Levy 9 and the 2013 Russian Chelyabinsk meteor—have drawn renewed attention to such threats, and advances in technology have opened up new possible options to deflect them from impact with the Earth.

Deflection efforts

Almost any deflection effort requires years of warning, allowing time to prepare and carry out a collision avoidance project. It has been estimated that a velocity change of just 3.5/t × 10⁻²ms⁻¹ (where t is the number of years until potential impact) is needed to successfully deflect a body on a direct collision trajectory. In addition, under certain circumstances, much smaller velocity changes are needed. For example, 99942 Apophis will swing by Earth in 2029, with a 10⁻⁴ probability of passing through a 'keyhole' and returning on an impact trajectory in 2035 or 2036 and could be deflected from this potential return trajectory several years before the swing by with a velocity change on the order of 10⁻⁶ms⁻¹

An impact by a 10 kilometres (6.2 mi) asteroid on the Earth is widely viewed as an extinction-level event, likely to cause catastrophic damage to the biosphere. Depending on speed, objects as small as 100 metres (330 ft) in diameter are historically extremely destructive. There is also the threat from comets coming into the inner Solar System. The impact speed of a long-period comet would likely be several times greater than that of a near-Earth asteroid, making its impact much more destructive; in addition, the warning time is unlikely to be more than a few months.

Finding out the material composition of the object is also necessary before deciding which strategy is appropriate. Missions like the 2005 Deep Impact probe have provided valuable information on what to expect.

History of government mandates

In a 1992 report to NASA, a coordinated Spaceguard Survey was recommended to discover, verify and provide follow-up observations for Earth-crossing asteroids. This survey was expected to discover 90% of these objects larger than one kilometer within 25 years. Three years later, another NASA report recommended search surveys that would discover 60-70% of short-period, near-Earth objects larger than one kilometer within ten years and obtain 90% completeness within five more years.

In 1998, NASA formally embraced the goal of finding and cataloging, by 2008, 90% of all near-Earth objects (NEOs) with diameters of 1 km or larger that could represent a collision risk to Earth. The 1 km diameter metric was chosen after considerable study indicated that an impact of an object smaller than 1 km could cause significant local or regional damage but is unlikely to cause a worldwide catastrophe. The impact of an object much larger than 1 km diameter could well result in worldwide damage up to, and potentially including, extinction of the human species. The NASA commitment has resulted in the funding of a number of NEO search efforts that are making considerable progress toward the 90% goal by 2008. The 2009 discovery of an NEO approximately 2 to 3 kilometers in diameter demonstrated there were still large objects to be detected.

U.S. Representative George E. Brown, Jr. (D-CA) was quoted as voicing his support for planetary defense projects in Air & Space Power Chronicles, saying "If some day in the future we discover well in advance that an asteroid that is big enough to cause a mass extinction is going to hit the Earth, and then we alter the course of that asteroid so that it does not hit us, it will be one of the most important accomplishments in all of human history."

Because of Congressman Brown's long-standing commitment to planetary defense, a U.S. House of Representatives' bill, H.R. 1022, was named in his honor: The George E. Brown, Jr. Near-Earth Object Survey Act. This bill "to provide for a Near-Earth Object Survey program to detect, track, catalogue, and characterize certain near-Earth asteroids and comets" was introduced in March 2005 by Rep. Dana Rohrabacher (R-CA). It was eventually rolled into S.1281, the NASA Authorization Act of 2005, passed by Congress on December 22, 2005, subsequently signed by the President, and stating in part:

The U.S. Congress has declared that the general welfare and security of the United States require that the unique competence of NASA be directed to detecting, tracking, cataloguing, and characterizing near-Earth asteroids and comets in order to provide warning and mitigation of the potential hazard of such near-Earth objects to the Earth. The NASA Administrator shall plan, develop, and implement a Near-Earth Object Survey program to detect, track, catalogue, and characterize the physical characteristics of near- Earth objects equal to or greater than 140 meters in diameter in order to assess the threat of such near-Earth objects to the Earth. It shall be the goal of the Survey program to achieve 90% completion of its near-Earth object catalogue (based on statistically predicted populations of near-Earth objects) within 15 years after the date of enactment of this Act. The NASA Administrator shall transmit to Congress not later than 1 year after the date of enactment of this Act an initial report that provides the following: (A) An analysis of possible alternatives that NASA may employ to carry out the Survey program, including ground-based and space-based alternatives with technical descriptions. (B) A recommended option and proposed budget to carry out the Survey program pursuant to the recommended option. (C) Analysis of possible alternatives that NASA could employ to divert an object on a likely collision course with Earth.

The result of this directive was a report presented to Congress in early March 2007. This was an Analysis of Alternatives (AoA) study led by NASA's Program Analysis and Evaluation (PA&E) office with support from outside consultants, the Aerospace Corporation, NASA Langley Research Center (LaRC), and SAIC (amongst others).

Ongoing projects

Number of NEOs detected by various projects.

The Minor Planet Center has been cataloging the orbits of asteroids and comets since 1947. It has recently been joined by surveys which specialize in locating the NEOs, many (as of early 2007) funded by NASA's Near Earth Object (NEO) program office as part of their Spaceguard program. One of the best-known is LINEAR that began in 1996. By 2004 LINEAR was discovering tens of thousands of objects each year and accounting for 65% of all new asteroid detections. LINEAR uses two one-meter telescopes and one half-meter telescope based in New Mexico.

Spacewatch, which uses a 90 centimeter telescope sited at the Kitt Peak Observatory in Arizona, updated with automatic pointing, imaging, and analysis equipment to search the skies for intruders, was set up in 1980 by Tom Gehrels and Dr. Robert S. McMillan of the Lunar and Planetary Laboratory of the University of Arizona in Tucson, and is now being operated by Dr. McMillan. The Spacewatch project has acquired a 1.8 meter telescope, also at Kitt Peak, to hunt for NEOs, and has provided the old 90 centimeter telescope with an improved electronic imaging system with much greater resolution, improving its search capability.

Other near-Earth object tracking programs include Near-Earth Asteroid Tracking (NEAT), Lowell Observatory Near-Earth-Object Search (LONEOS), Catalina Sky Survey, Campo Imperatore Near-Earth Objects Survey (CINEOS), Japanese Spaceguard Association, and Asiago-DLR Asteroid Survey. Pan-STARRS completed telescope construction in 2010, and it is now actively observing.

"Spaceguard" is the name for these loosely affiliated programs, some of which receive NASA funding to meet a U.S. Congressional requirement to detect 90% of near-Earth asteroids over 1 km diameter by 2008. A 2003 NASA study of a follow-on program suggests spending US$250–450 million to detect 90% of all near-Earth asteroids 140 meters and larger by 2028.

NEODyS is an online database of known NEOs.

Prospective projects

Orbit@home intends to provide distributed computing resources to optimize search strategy, though as of 2012 it is seeking funding.

The Large Synoptic Survey Telescope, currently under construction, is expected to perform a comprehensive, high-resolution survey starting in the late 2010s.

The Asteroid Terrestrial-impact Last Alert System, currently in development, is expected to conduct frequent scans of the sky with a view to later-stage detection.

Detection from space

On November 8, 2007, the House Committee on Science and Technology's Subcommittee on Space and Aeronautics held a hearing to examine the status of NASA's Near-Earth Object survey program. The prospect of using the Wide-field Infrared Survey Explorer was proposed by NASA officials.

WISE surveyed the sky in the infrared band at a very high sensitivity. Asteroids that absorb solar radiation can be observed through the infrared band. It was used to detect NEOs, in addition to performing its science goals. It is projected that WISE could detect 400 NEOs (roughly two percent of the estimated NEO population of interest) within the one-year mission.

NEOSSat, the Near Earth Object Surveillance Satellite, is a microsatellite launched in February 2013 by the Canadian Space Agency (CSA) that will hunt for NEOs in space.

Results

Research published in the March 26, 2009 issue of the journal Nature, describes how scientists were able to identify an asteroid in space before it entered Earth’s atmosphere, enabling computers to determine its area of origin in the Solar System as well as predict the arrival time and location on Earth of its shattered surviving parts. The four-meter-diameter asteroid, called 2008 TC₃, was initially sighted by the automated Catalina Sky Survey telescope, on October 6, 2008. Computations correctly predicted impact would occur 19 hours after discovery in the Nubian Desert of northern Sudan.

A number of potential threats have been identified, such as 99942 Apophis (previously known by its provisional designation 2004 MN₄), which had been given an impact probability of about 3% for the year 2029. This probability has been revised to zero on the basis of new observations.

Impact probability calculation pattern

Why asteroid impact probability goes up, then down.

The ellipses in the diagram at right show the likely asteroid position at closest Earth approach. At first, with only a few asteroid observations, the error ellipse is very large and includes the Earth. Further observations shrink the error ellipse, but it still includes the Earth. This raises the impact probability, since the Earth now covers a larger fraction of the error region. Finally, yet more observations (often radar observations, or discovery of a previous sighting of the same asteroid on archival images) shrink the ellipse until the Earth is outside the error region, and the impact probability returns to near zero.

Collision avoidance strategies

Various collision avoidance techniques have different trade-offs with respect to metrics such as overall performance, cost, operations, and technology readiness. There are various methods for changing the course of an asteroid/comet. These can be differentiated by various types of attributes such as the type of mitigation (deflection or fragmentation), energy source (kinetic, electromagnetic, gravitational, solar/thermal, or nuclear), and approach strategy (interception, rendezvous, or remote station). Strategies fall into two basic sets: destruction and delay.

Destruction concentrates on rendering the impactor harmless by fragmenting it and scattering the fragments so that they miss the Earth or burn up in the atmosphere.

Collision avoidance strategies can also be seen as either direct, or indirect. The direct methods, such as nuclear bombs or kinetic impactors, violently intercept the bolide's path. Direct methods are preferred because they are generally less costly in time and money. Their effects may be immediate, thus saving precious time. These methods might work for short-notice, or even long-notice threats, from solid objects that can be directly pushed, but probably not effective against loosely aggregated rubble piles. The indirect methods, such as gravity tractors, attaching rockets or mass drivers, laser cannon, etc., will travel to the object then take more time to change course up to 180 degrees to fly alongside, and then will also take much more time to change the asteroid's path just enough so it will miss Earth.

Many NEOs are "flying rubble piles" only loosely held together by gravity, and a deflection attempt might just break up the object without sufficiently adjusting its course. If an asteroid breaks into fragments, any fragment larger than 35 m across would not burn up in the atmosphere and itself could impact Earth. Tracking the thousands of fragments that could result from such an explosion would be a very daunting task.

Delay exploits the fact that both the Earth and the impactor are in orbit. An impact occurs when both reach the same point in space at the same time, or more correctly when some point on Earth's surface intersects the impactor's orbit when the impactor arrives. Since the Earth is approximately 12,750 km in diameter and moves at approx. 30 km per second in its orbit, it travels a distance of one planetary diameter in about 425 seconds, or slightly over seven minutes. Delaying, or advancing the impactor's arrival by times of this magnitude can, depending on the exact geometry of the impact, cause it to miss the Earth.

Nuclear explosive device

See also: B83 nuclear bomb, nuclear pulse propulsion, and Project Excalibur

Initiating a nuclear explosive device above, on, or slightly beneath, the surface of a threatening celestial body, is a potential deflection option, with the optimal detonation height dependent upon the composition and size of the object. In the case of an inbound threat from a "rubble pile" the stand off, or detonation height above the surface configuration has been put forth as a means to prevent the potential fracturing of the rubble pile, the detonations energetic release of neutrons and soft X-rays, which do not appreciably penetrate matter, are converted into thermal heat upon encountering the objects surface matter, ablatively vaporizing all line of sight exposed surface areas of the object to a shallow depth, turning the surface material it heats up into ejecta, and analogous to the ejecta from a chemical rocket engine exhaust, changing the velocity, or "nudging", the object off course by the reaction, following Newton's third law, with ejecta going one way and the object being propelled in the other.

It does not require the entire NEO to be vaporized to mitigate an impact threat, the resulting objects small reduction in mass that followed the nuclear devices energetic thermal blast and the created rocket exhaust effect, an effect created by the high velocity of the objects now vaporized mass ejecta, could produce sufficiently positive results.

If the object is very large but is still a loosely held together rubble pile, a solution is to detonate a series of nuclear explosive devices alongside the asteroid, far enough away as not to fracture the potentially loosely held together object. Providing this stand-off strategy was done far enough in advance, the force from any number of nuclear blasts would be enough to alter the object's trajectory to avoid an impact. By the 2020s NASA has concluded that the nuclear stand off option can deflect NEOs of 100-500 meter diameters two years before the estimated earth impact, and larger NEOs with a five year warning.

A NASA analysis of deflection alternatives, conducted in 2007, stated:

Nuclear standoff explosions are assessed to be 10-100 times more effective than the non-nuclear alternatives analyzed in this study. Other techniques involving the surface or subsurface use of nuclear explosives may be more efficient, but they run an increased risk of fracturing the target NEO. They also carry higher development and operations risks.

In 2011, Bong Wie, director of the Asteroid Deflection Research Center at Iowa State University, studied strategies to respond to a threatening asteroid on short notice of a year or so, and determined that to provide the required energy, a nuclear explosion is likely the only thing that would work against a very large asteroid in this short time frame. Other systems designed to divert an asteroid such as tugboats, gravity tractors, solar sails and mass drivers require 10 or 20 years of advance notice. Wie's conceptual Hypervelocity Asteroid Intercept Vehicle (HAIV) mission architecture to deal with large asteroids, combines a kinetic impactor that creates an initial crater for a follow up subsurface nuclear detonation within that initial crater, which would create a high degree of efficiency in the conversion of the nuclear energy that is released in the detonation into propulsion energy to the asteroid. Another proposed approach along similar lines is the use of a surface detonating nuclear device, in place of the prior mentioned kinetic impactor, in order to create the initial crater, with the resulting crater that forms then again being used as a rocket nozzle to channel succeeding nuclear detonations.

The 1964 book Islands in Space calculates that the nuclear megatonnage necessary for several deflection scenarios exists. In 1967, graduate students under Professor Paul Sandorff at the Massachusetts Institute of Technology designed a system using rockets and nuclear explosions to prevent a hypothetical impact on Earth by the 1.4 kilometer wide asteroid 1566 Icarus, an object which routinely makes lunar distance wide, or greater, approaches to Earth every couple of years. This design study was later published as Project Icarus which served as the inspiration for the 1979 film Meteor.

The use of nuclear explosive devices is an international issue and will need to be addressed by the United Nations Committee on the Peaceful Uses of Outer Space. The 1996 Comprehensive Nuclear-Test-Ban Treaty technically bans nuclear weapons in space. However it is unlikely that a nuclear explosive device, fuzed to be detonated only upon interception with a threatening celestial object, with the sole intent of preventing that celestial body from impacting earth would be regarded as an un-peaceful use of space, or that the explosive device designed to mitigate the impact, explicitly designed to prevent harm to come to life would fall under the classification of a "weapon".

Kinetic impact

See also: ramming and Deep Impact (spacecraft)

The Deep Impact collision encounter with comet Tempel 1. The impact flash and resulting ejecta is clearly visible. The impactor delivered the equivalent of 4.7 tons of TNT upon impact. Changing the orbit of the comet by about 10 cm (3.9 in)."

The 2005 Deep Impact relayed recording from the Impactor Targeting Sensor, depicting the impact phase of the mission.

The impact of a massive object, such as a spacecraft or even another near-Earth object, is another possible solution to a pending NEO impact. An object with a high mass close to the Earth could be sent out into a collision course with the asteroid, knocking it off course.

When the asteroid is still far from the Earth, a means of deflecting the asteroid is to directly alter its momentum by colliding a spacecraft with the asteroid.

A NASA analysis of deflection alternatives, conducted in 2007, stated:

Non-nuclear kinetic impactors are the most mature approach and could be used in some deflection/mitigation scenarios, especially for NEOs that consist of a single small, solid body.

The European Space Agency (ESA) is already studying the preliminary design of a space mission able to demonstrate this futuristic technology. The mission, named Don Quijote, is the first real asteroid deflection mission ever designed. ESA's Advanced Concepts Team has also demonstrated theoretically that a deflection of 99942 Apophis could be achieved by sending a simple spacecraft weighing less than one ton to impact against the asteroid. During a trade-off study one of the leading researchers argued that a strategy called 'kinetic impactor deflection' was more efficient than others.

Asteroid gravitational tractor

Main article: Gravitational tractor

One more alternative to explosive deflection is to move the asteroid slowly over a time. Tiny constant thrust accumulates to deviate an object sufficiently from its predicted course. Edward T. Lu and Stanley G. Love have proposed using a large heavy unmanned spacecraft hovering over an asteroid to gravitationally pull the latter into a non-threatening orbit. The spacecraft and the asteroid mutually attract one another. If the spacecraft counters the force towards the asteroid by, e.g., an ion thruster, the net effect is that the asteroid is accelerated towards the spacecraft and thus slightly deflected from its orbit. While slow, this method has the advantage of working irrespective of the asteroid composition or spin rate – rubble pile asteroids would be difficult or impossible to deflect by means of nuclear detonations while a pushing device would be hard or inefficient to mount on a fast rotating asteroid. A gravity tractor would likely have to spend several years beside the asteroid to be effective.

A NASA analysis of deflection alternatives, conducted in 2007, stated:

"Slow push" mitigation techniques are the most expensive, have the lowest level of technical readiness, and their ability to both travel to and divert a threatening NEO would be limited unless mission durations of many years to decades are possible.

According to Rusty Schweickart, the gravitational tractor method is also controversial because during the process of changing an asteroid's trajectory the point on Earth where it could most likely hit would be slowly shifted across different countries. It means that the threat for the entire planet would be minimized at the cost of some specific states' security. In Schweickart's opinion, choosing the way the asteroid should be "dragged" would be a tough diplomatic decision.

Ion beam shepherd

Main article: Ion Beam Shepherd

Another "contactless" asteroid deflection technique has been recently proposed by C.Bombardelli and J.Peláez from the Technical University of Madrid. The method involves the use of a low divergence ion thruster pointed at the asteroid from a nearby hovering spacecraft. The momentum transmitted by the ions reaching the asteroid surface produces a slow but continuous force that can deflect the asteroid in a similar way as done by the gravity tractor but with a lighter spacecraft.

Use of focused solar energy

NASA study of a solar sail. The sail would be 0.5 km wide.

H. Jay Melosh proposed to deflect an asteroid or comet by focusing solar energy onto its surface to create thrust from the resulting vaporization of material, or to amplify the Yarkovsky effect. Over a span of months or years enough solar radiation can be directed onto the object to deflect it.

This method would first require the construction of a space station with a system of gigantic lens and magnifying glasses near the Earth. Then the station would be transported toward the Sun.

Mass driver

A mass driver is an (automated) system on the asteroid to eject material into space thus giving the object a slow steady push and decreasing its mass. A mass driver is designed to work as a very low specific impulse system, which in general uses a lot of propellant, but very little power.

The idea is that when using local material as propellant, the amount of propellant is not as important as the amount of power, which is likely to be limited.

Another possibility is to use a mass driver on the moon aimed at the NEO to take advantage of the moon's orbital velocity and inexhaustible supply of "rock bullets".

Conventional rocket engine

Attaching any spacecraft propulsion device would have a similar effect of giving a steady push, possibly forcing the asteroid onto a trajectory that takes it away from Earth. An in-space rocket engine that is capable of imparting an impulse of 10⁶ N·s (E.g. adding 1 km/s to a 1000 kg vehicle), will have a relatively small effect on a relatively small asteroid that has a mass of roughly a million times more. Chapman, Durda, and Gold's white paper calculates deflections using existing chemical rockets delivered to the asteroid.

Other proposals

One method of changing a large threatening celestial body's orbit would be, by capturing relatively smaller celestial objects and using those, and not the usually proposed small bits of spacecraft, as the means of creating a powerful kinetic impact, or alternatively, a stronger faster acting gravitational tractor.

• Non-conventional engines, such as VASIMR
• Wrapping the asteroid in a sheet of reflective plastic such as aluminized PET film as a solar sail
• "Painting" or dusting the object with titanium dioxide (white) or soot (black) to alter its trajectory via the Yarkovsky effect.
• Planetary scientist Eugene Shoemaker in 1996 proposed deflecting a potential impactor by releasing a cloud of steam in the path of the object, hopefully gently slowing it. Nick Szabo in 1990 sketched a similar idea, "cometary aerobraking", the targeting of a comet or ice construct at an asteroid, then vaporizing the ice with nuclear explosives to form a temporary atmosphere in the path of the asteroid.
• Attaching a tether and ballast mass to the asteroid to alter its trajectory by changing its center of mass.
• Laser ablation
• Magnetic Flux Compression

Deflection technology concerns

Carl Sagan, in his book Pale Blue Dot, expressed concerns about deflection technology: that any method capable of deflecting impactors away from Earth could also be abused to divert non-threatening bodies toward the planet. Considering the history of genocidal political leaders and the possibility of the bureaucratic obscuring of any such project's true goals to most of its scientific participants, he judged the Earth at greater risk from a man-made impact than a natural one. Sagan instead suggested that deflection technology should only be developed in an actual emergency situation.

Analysis of the uncertainty involved in nuclear deflection shows that the ability to protect the planet does not imply the ability to target the planet. A nuclear bomb which changed an asteroid's velocity by 10 meters/second (plus or minus 20%) would be adequate to push it out of an Earth-impacting orbit. However, if the uncertainty of the velocity change was more than a few percent, there would be no chance of directing the asteroid to a particular target.

According to Rusty Schweickart, the gravitational tractor method is also controversial because during the process of changing an asteroid's trajectory the point on Earth where it could most likely hit would be slowly shifted across different countries. It means that the threat for the entire planet would be minimized at the cost of some specific states' security. In Schweickart's opinion, choosing the way the asteroid should be "dragged" would be a tough diplomatic decision.

Planetary defense timeline

• In their 1964 book, Islands in Space, Dandridge M. Cole and Donald W. Cox noted the dangers of planetoid impacts, both those occurring naturally and those that might be brought about with hostile intent. They argued for cataloging the minor planets and developing the technologies to land on, deflect, or even capture planetoids.
• In the 1980s NASA studied evidence of past strikes on planet Earth, and the risk of this happening at our current level of civilization. This led to a program that maps which objects in the Solar System both cross Earth's orbit and are large enough to cause serious damage if they ever hit.
• In the 1990s, US Congress held hearings to consider the risks and what needed to be done about them. This led to a US$3 million annual budget for programs like Spaceguard and the near-Earth object program, as managed by NASA and USAF.
• In 2005 the world's astronauts published an open letter through the Association of Space Explorers calling for a united push to develop strategies to protect Earth from the risk of a cosmic collision.
• It is currently (as of late 2007) believed that there are approximately 20,000 objects capable of crossing Earth's orbit and large enough (140 meters or larger) to warrant concern. On the average, one of these will collide with Earth every 5,000 years, unless preventative measures are undertaken. It is now anticipated that by year 2008, 90% of such objects that are 1 km or more in diameter will have been identified and will be monitored. The further task of identifying and monitoring all such objects of 140m or greater is expected to be complete around 2020.
• The Catalina Sky Survey (CSS) is one of NASA´s four funded surveys to carry out a 1998 U.S. Congress mandate to find and catalog by the end of 2008, at least 90 percent of all near-Earth objects (NEOs) larger than 1 kilometer across. CSS discovered 310 NEOs in 2005, 400 in 2006 and the record will be broken with 450 NEOs found in 2007. In doing this survey they discovered on November 20, 2007, an asteroid, designated 2007 WD₅, which initially was estimated to have a chance of hitting Mars on January 30, 2008, but further observations during the following weeks allowed NASA to rule out an impact. NASA estimated a near miss by 26,000 kilometres (16,000 mi).
• In January 2012, after a near pass-by of object 2012 BX34, a paper entitled “A Global Approach to Near-Earth Object Impact Threat Mitigation,” is released by researchers from Russia, Germany, the United States, France, Britain and Spain which discusses the “NEOShield” project.

Fictional representations

Asteroid or comet impacts are a common subgenre of disaster fiction, and such stories typically feature some attempt—successful or unsuccessful—to prevent the catastrophe. Most involve trying to destroy or explosively redirect an object, perhaps understandably from the direction of dramatic interest. (See also Asteroids in fiction –Collisions with Earth).

Film

• When Worlds Collide (1951): A science fiction film based on the 1933 novel; shot in Technicolor, directed by Rudolph Maté and the winner of the 1952 Academy Awards for special effects.
• Crash of the Moons (1954): A 75-minute US science fiction film, consisting of three consecutive episodes of the TV series Rocky Jones, Space Ranger.
• Meteor (1979): A series of orbital platforms armed with nuclear missiles are used to deflect an asteroid.
• Gorath (1980): Astronauts, originally sent to collect data on Saturn, are diverted to investigate the mysterious star Gorath, reported as being 6,000 times the size of the Earth, which is predicted to come dangerously close to Earth. The astronauts radio back data about the star, and the world is stunned by the discovery. The United Nations band together to discover a solution to the problem, and decide that their only solutions are to either destroy the star or move the planet out of its way.
• Starship Troopers (1997): Insect-like aliens launch an asteroid at Earth, obliterating Buenos Aires. Shortly afterward, orbital defenses are constructed to destroy any future asteroids the aliens may send.
• Armageddon (1998): A pair of newly-modified space shuttles are used to drill a hole in an asteroid and plant a nuclear bomb, allowing Bruce Willis to save the planet.
• Deep Impact (1998): A manned spacecraft plants a number of nuclear bombs on a comet and is mostly successful.
• Judgment Day (1999): Cultists seize the only man capable of devising a way to stop a giant meteor from hitting the Earth. A female agent teams up with a prisoner (Ice-T), who together have three days to rescue the scientist and save the planet from extinction.
• Post Impact (2004) A disaster film centered on the story of a man forced to leave his family behind during a massive impact event.
• Earthstorm (2006): Asteroid impact on the lunar surface and a resulting debris storm that strikes the Earth, inflicting severe damage. Scientists, along with a bombing expert, bind the Moon's core, thereby avoiding a global catastrophe.
• Seeking a friend for the end of the world (2012): Comedy-drama set during the last weeks before an asteroid hits Earth.
• Iron Sky (2012): Nazi army from the Moon tows asteroids and pieces of Moon rock to drop them on Earth cities.

Literature

See also: Asteroids in fiction –Collisions with planets

• The Moon Is a Harsh Mistress (1966): A lunar colony revolts against authoritarian Earth rule, using a catapult designed for sending grain shipments to earth to throw moon rocks at the earth instead. Written by Robert A. Heinlein.
• The Mote in God's Eye (1974): Features the examination of an alien war that culminates in the use of asteroids for planetary bombardment and the near extinction of the warring species. Written by Larry Niven and Jerry Pournelle.
• Lucifer's Hammer (1977): A comet, which was initially thought unlikely to strike, hits the Earth, resulting in the end of civilization and a decline into tribal warfare over food and resources. Written by Larry Niven and Jerry Pournelle.
• Shiva Descending (1980): A swarm of meteors is falling on Earth, but a giant comet, Shiva, is still coming. Written by Gregory Benford and William Rotsler.
• Footfall (1985): An alien race uses controlled meteorite strikes as well as a large asteroid superweapon against Earth. Written by Larry Niven and Jerry Pournelle.
• The Hammer of God (1993): A spacecraft is sent to divert a massive asteroid by using thrusters. Written by Arthur C. Clarke.
• Moonfall (1998): A comet is in collision course with the Moon. After the collision, the debris start falling on Earth. Written by Jack McDevitt.
• Nemesis (1998): The US government gathers a small team, including a British astronomer, with instructions to find and deflect an asteroid already targeted at North America by the Russians. Written by British astronomer Bill Napier.
• Terraforming Earth (2001): An asteroid impact wipes out most life on Earth. The only remaining humans are a small group of clones on an automated moon base, tasked with rebuilding civilization. Written by Jack Williamson.

Television

• Star Trek: In "The Paradise Syndrome" (1968), an amnesiac Kirk finds a centuries-old obelisk which has a deflector beam built in to deflect an asteroid coming to wipe out a primitive race.
• Horizon: Hunt for the Doomsday Asteroid (1994), a BBC documentary, part of the Horizon science series, Season 30, Episode 7.
• The Simpsons: In "Bart's Comet" (1995), Bart discovers a comet that is heading directly for Springfield. The town attempts to destroy it with a rocket, but it misses. The comet ends up being destroyed by an extra thick layer of pollution over the city.
• NOVA: Doomsday Asteroid (1995), a PBS NOVA science documentary, Series 23, Episode 4.
• Cowboy Bebop: The series shows an Earth with a shattered moon and several of its fragments remaining in Earth's orbit. The episode "Hard Luck Woman" (1998) focuses on Ed's father, who is constantly updating Earth's geographical map by tracking moon fragments that fall on Earth.
• Asteroid (1998), a NBC TV movie, features two large asteroid fragments on collision courses with the Earth. The U.S. government attempts to break the larger of the two fragments apart with airborne lasers.
• Futurama: The episode "A Big Piece of Garbage" (1999), features a large space object on a collision course with Earth which turns out to be a giant ball of garbage launched into space by New York around 2052. Residents of New New York first try blowing up the ball to destroy it but fail as the rocket is absorbed by the ball. They then deflect it using a newly created near-identical garbage ball.
• Power Rangers: Lightspeed Rescue: In "The Omega Project" (2000), a meteor is sent towards Earth by evil space aliens, but is blown up by Omegazords.
• Defenders of the Planet (2001), a three-part British TV mini-series discussing the individuals and organizations working to defend the Earth against killer asteroids and other extraterrestrial threats; broadcast on The Learning Channel.
• Stargate SG-1: The episode "Fail Safe" (2002) features an asteroid on a collision course with the Earth.
• Kirby: Right Back At Ya! (2002): Mabel, a fortune teller in Kirby: Right Back At Ya! predicts an asteroid headed straight for Pop Star, but it is not due for impact for another 10,000 years. But Nightmare Enterprises speeds it up, and thus it will collide in 48 hours. Luckily, a few brave citizens form a plan to deflect the asteroid by firing at it with cannons. When the cannon shots fail to hit their target, Kirby inhales them, shoots them back and sends the massive space object back into orbit.
• Stratos 4 (2003): In this anime, a two-staged space and air defense network is established in order to prevent a large group of comets colliding with Earth.
• Justice League (TV series) (2003): In the episode "Maid of Honor," Vandal Savage, king of Kasnia, pretends to be participating in the peaceful expansion of the International Space Station while secretly turning it into a mass driver. He then takes control of the station and threatens to launch asteroids at specific countries on Earth if the international community does not comply with his demands.
• Star Trek: Enterprise: The episode "Terra Prime" (2005) features a domestic xenophobic terrorist organization taking control of the Large Veteron Array on Mars for the purpose of threatening to destroy Starfleet Command. To initiate an undetected sneak attack, members of the Enterprise use a shuttlepod to hide in the wake of an ice asteroid which was intentionally redirected by the Array years earlier to impact with Mars in order to help with terraforming. There is an implied threat that if the terrorists did not maneuver the asteroid correctly, it might accidentally hit near the Mars colony. The asteroid does hit in the correct location, with the crew on the shuttlepod surviving by breaking away at the last moment, successfully remaining undetected.
• Deadly Skies (2006): a science-fiction television film showing the effort of two astronomers and two military men to stop a giant asteroid on a collision course with Earth.
• Impact Earth (2007) (a.k.a. Futureshock: Comet): A comet fragment strike in the Atlantic Ocean destroys Shannon Airport, Ireland with a tsunami. They discover it was from a long-period comet that was a Sun Grazer and then discover that it was only a small part and the rest was coming a year later. There is an argument between the main hero scientist as to the efficacy of a nuclear deflection strategy, but they discover in the nick of time that a nuclear bomb would make it worse, so they implement an evacuation strategy and allow it to hit, in Pittsburgh.
• Danny Phantom: The series finale, "Phantom Planet" (2007) involved a giant asteroid of the fictional element ecto-ranium from the rings of Saturn almost collide with Earth. This was solved when ghosts had made the planet intangible, hence the title.
• The Sarah Jane Adventures: In "Whatever Happened to Sarah Jane?" (2007), a meteor on a collision course with the Earth is ultimately deflected back into space by Sarah Jane's alien computer, Mr. Smith.
• Meteor (2009): A large earth-grazing meteor enters the Earth's atmosphere for several minutes and is ultimately deflected back into space using a combined nuclear attack by the United States, Russia, and China.

Games

• Asteroids by Atari (1979): The object of the game is to shoot and destroy asteroids and saucers while not colliding with either, or being hit by the saucers' counter-fire.
• Outpost (1994) and Outpost 2 (1997): The player of these two colonization PC games from Sierra Entertainment is given the task of building and managing a space colony in the aftermath of humanity's certain extinction caused by an asteroid collision.
• The Dig (1995): In this adventure PC game from LucasArts, three of five astronauts assigned to blow an asteroid off-course are transported to a distant world.
• Homeworld (1999): At the outskirts of the Hiigaran system, the Taiidan attempted to destroy the Kushan Mothership in a last-ditch effort using a large asteroid (somewhere between 15 and 20 km across) with an engine on its back. The asteroid had enough mass and kinetic energy to completely vaporize anything it collided with and was capable of withstanding the combined firepower of the whole Kushan fleet for minutes.
• Submarine TITANS (2000): A real time strategy game by Ellipse Studios in which the Earth is devastated in 2047 by the impact of the Clark Comet and the attached Silicon spacecraft. The impact of the Clark Comet also deposits significant amounts of the fictional element Corium 276, which factors heavily into both the gameplay and the plot of Submarine TITANS.
• Ace Combat 04: Shattered Skies (2001): In this combat flight simulator for the PlayStation 2 by Namco, a railgun battery is used in an attempt to destroy a massive asteroid with limited success.
• Mass Effect (2007): The "Bring Down the Sky" expansion features an alien extremist group that attempts to hijack an asteroid station and set it on a collision course with a human colony.
• Advance Wars: Days of Ruin (2008): Almost 90% of mankind has been killed off following devastating meteor strikes which have destroyed much of civilization and caused a massive dust cloud to blot out the Sun. The player takes the role of a military leader and tries to protect the survivors in the ruins of civilization.
• "Rage (video game)" (2011): Asteroid 99942 Apophis impacts the Earth and the technology used to ensue mankind's survival is to keep people in cryogenic sleep until the Earth was safe again.

See also

• Asteroid mining
• B612 Foundation
• Cando event
• Chicxulub Crater
• Comet Shoemaker-Levy 9 which collided with Jupiter in 1994
• Dinosaur extinction theory first explained by Walter Alvarez
• Doomsday event
• Earth-crosser asteroid
• Eastern Mediterranean Event
• Gravitational tractor
• Gravity tractor
• Impact events
• Lincoln Near-Earth Asteroid Research (LINEAR)
• List of impact craters on Earth
• Near-Earth asteroid
• NEOShield
• Palermo scale
• Potentially hazardous object
• Torino Scale
• Tunguska event
• Vitim event
• Don Quijote (spacecraft)

References

Citations

Bibliography

• Luis Alvarez et al. 1980 paper in Science magazine on the great mass extinction 65 million years ago that led to the proliferation of mammal species such as the rise of the human race, thanks to asteroid-impact, a controversial theory in its day, now generally accepted.
• Christopher D. Hall and I. Michael Ross, "Dynamics and Control Problems in the Deflection of Near-Earth Objects," Advances in the Astronautical Sciences: Astrodynamics 1997, Vol.97, Part I, 1997, pp.613–631. The first known study by the US Air Force and US Navy on how to deflect NEOs.
• Izzo, D., Bourdoux, A., Walker, R. and Ongaro, F.; "Optimal Trajectories for the Impulsive Deflection of NEOs"; Paper IAC-05-C1.5.06, 56th International Astronautical Congress, Fukuoka, Japan, (October 2005). Later published in Acta Astronautica, Vol. 59, No. 1-5, pp. 294–300, April 2006, available in http://www.esa.int/gsp/ACT/publications/pub-mad.htm – The first scientific paper proving that Apophis can be deflected by a small sized kinetic impactor.
• Clark R. Chapman, Daniel D. Durda & Robert E. Gold (February 24, 2001) Impact Hazard, a Systems Approach, white paper on public policy issues associated with the impact hazard, at http://www.boulder.swri.edu/clark/neowp.html
• Dandridge M. Cole and Donald W. Cox. 1964. Islands in Space: The Challenge of the Planetoids Philadelphia: Chilton. ASIN: B0007DZSR0. First major book on asteroids, covering threat of impact and feasibility of deflection or even capture. Cox and Chestek (following) is a later revision of this book.
• Donald W. Cox, and James H. Chestek. 1996. Doomsday Asteroid: Can We Survive? New York: Prometheus Books. ISBN 1-57392-066-5. (Note that despite its sensationalist title, this is a good treatment of the subject and includes a nice discussion of the collateral space development possibilities.)
• David Morrison Is the Sky Falling?, Skeptical Inquirer 1997.
• David Morrison, Alan W Harris, Geoff Summer, Clark R. Chapman, & Andrea Carusi Dealing with Impact Hazard, 2002 technical summary http://impact.arc.nasa.gov/downloads/NEO_Chapter_1.pdf?ID=113
• Russell L. Schweickart, Edward T. Lu, Piet Hut and Clark R. Chapman; "The Asteroid Tugboat"; Scientific American (November 2003).
• Kunio M. Sayanagi "How to Deflect an Asteroid" Ars Technica (April 2008).
• Edward T. Lu and Stanley G. Love A Gravitational Tractor for Towing Asteroids; http://arxiv.org/ftp/astro-ph/papers/0509/0509595.pdf

Further reading

General

• Air Force 2025. Planetary Defense: Social, Economic, and Political Implications, United States Air Force, Air Force 2025 Final Report webpage, December 11, 1996.
• Belton, M.J.S. Mitigation of Hazardous Comets and Asteroids, Cambridge University Press, 2004, ISBN 0521827647, ISBN 978-0521827645
• Bottke, William F. Asteroids III (Space Science Series), University of Arizona space science series, University of Arizona Press, 2002, ISBN 0816522812, ISBN 978-0816522811
• Lewis, John S. Comet and Asteroid Impact Hazards on a Populated Earth: Computer Modeling (Volume 1 of Comet and Asteroid Impact Hazards on a Populated Earth: Computer Modeling), Academic Press, 2000, ISBN 0124467601, ISBN 978-0124467606
• Verschuur, Gerrit L. Impact!: The Threat of Comets and Asteroids, Oxford University Press, ISBN 0195353277, 1997, ISBN 978-0195353273

Effects of asteroid and meteorite strikes

• Daugherty, Laura and Emily Van Yuga. What Damage Have Impacts Done to Humans in Recorded History? (Geol 117: Meteorite Impacts in Space and Time), Oberlin College Geology Department, Oberlin College, May 11, 2001.
• Halliday, I., A.T. Blackwell, and A.A. Griffin. "Meteorite Impacts on Humans and Buildings", Nature, pp. 318–317. [bib. of Yau et al.]
• Lapaz, L. "Effects of Meteorites on the Earth", Advances in Geophysics, Vol. 4, pp. 217–350. [bib. of Yau et al.]
• Lewis, J.S. Rain of Iron and Ice: The Very Real Threat of Comet and Asteroid Bombardment, Reading, MA: Addison-Wesley Pub. Co., 1996; Basic Books, 1997, ISBN 0201154943, ISBN 978-0201154948. [OBIS]
• Nield, Ted. Don't wrong the meteorite: Ted Nield thinks it's time to reassess our attitude to cosmic impacts. Meteorites are our friends, Geoscientist Online, The Geological Society, October 2008.
• Norton, O.R. "Rocks from Space". Missoula Montana: Mountain Press Publishing Company, 1998. [course textbook].
• Reimold, W. U. and R. L. Gibson, Anton Pelser, Mauritz Naudé, Kevin Balkwill. Meteorite impact!: the danger from space and South Africa's mega-impact the Vredefort structure, Chris van Rensburg, 2005, ISBN 1919908625, ISBN 9781919908625.
• "Special Report: Death and Property Damage Due to Meteor Destruction", UFO Research: Cincinnati!, November, 1998.
• Swindel, G.W. Jr., and W.B. Jones. Meteoritics, Vol. 1, pp. 125–132. [bib. of Lapaz 1958].
• Webb, S.K. A Novel Measure of Meteorite Flux", [meteorite-list] How Many Meteorites Fall?, November 30, 2000.
• Worthey, G. Meteor Near Misses and Strikes, St. Ambrose University Astronomy, 11 October 1999.
• Yau, K., Weissman, P., & Yeomans, D. Meteorite Falls In China And Some Related Human Casualty Events, Meteoritics, 1994, Vol. 29, No. 6, pp. 864–871, ISSN: 0026-1114, bibliographic code: 1994Metic..29..864Y.

External links

• "Deflecting Asteroids," by Gregory L. Matloff, IEEE Spectrum, April 2012
• PlanetaryDefense Blog
• B612 Foundation, has a goal to significantly alter the orbit of an asteroid, in a controlled manner, by 2015.
• European Space Agency's ACT – May we deflect Asteroids? (what the Dinosaurs did not know!!)
• Asteroid belt collision generates dust cloud around Earth causing climate change a few million years ago.
• Asteroid Occultation Updates
• BBC Horizon – Averting Armageddon (summary)
• Best Astronomy web sites
• British Government FAQ on Near Earth Orbit risks
• Doomsday Asteroid dot Com
• Future Asteroid Interception Research
• Killer Asteroids and You
• Lifeboat Foundation AsteroidShield
• LINEAR a USAF NASA joint effort operated by M.I.T. Lincoln Laboratory.
• Meteorite FAQ
• NASA Asteroid and Comet Hazards
• Near Earth Asteroid principal investigator Raymond Bambery interviewed by Earth and Sky
• Near Earth Objects Directory also here.
• NASA Near-Earth Object Program
• NEAR-Shoemaker, NASA space mission to study asteroid Eros for one year.
• NEAT (Near Earth Asteroid Tracking) by GEODSS {USAF/Ground-based Electro-Optical Deep Space Surveillance} under the 21st Space Wing, headquartered at Peterson Air Force Base, Colorado.
  • NEAT on MSS (Maui Space Surveillance System 1.2-m telescope)
• PERMANENT (Projects to Employ Resources of the Moon and Asteroids Near Earth in the Near Term)
• Simulate the collision of an asteroid or a comet with any planet in Solar System, or calculate effects based on size and speed of the bombardment, and how far witness is from impact site.
• Space Watch Observatory at University of Arizona
• Nasa's 2007 Report to Congress on NEO Survey Program Including Tracking and Diverting Methods for High Risk Asteroids
• The Planetary Society Apophis Mission Design Competition
• Consolidated Risk Tables: Asteroid/Comet Connection
• Armagh University: Near Earth Object Impact Hazard
• Planetary Defense Foundation

Relevant conferences

• 2009 International Academy of Astronautics (IAA) Planetary Defense Conference
• 2009 University of Nebraska College of Law Conference on NEO Law and Policy
• 2007 Planetary Defense Conference
• 2004 Planetary Defense Conference

International Spaceguard organizations

• Australian SpaceGuard
• British SpaceGuard
• EARN (European Asteroid Research Node)
• IAU (International Astronomical Union) Working Group on Near Earth Objects.
• Spaceguard Foundation
  • SpaceGuard Foundation's Tumbling Stone on-Line Magazine