Asteroid impact avoidance comprises a number of methods by which near-Earth objects (NEO) could be diverted, preventing destructive impact events. A sufficiently large impact by an asteroid or other NEOs would cause, depending on its impact location, massive tsunamis, multiple firestorms and an impact winter caused by the sunlight blocking effect of placing large quantities of pulverized rock dust into the stratosphere. Massive impacts may also cause volcanic mantle pluming at the antipodal point. This volcanism, if energetic enough, could compound the effects of the impact by creating a volcanic winter, irrespective of the other impact effects. A collision between the Earth and an approximately 10-kilometre-wide object 66 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 a major collision are not great in the near term, there is a high probability that one will happen eventually unless defensive actions are taken. Recent astronomical events—such as the Shoemaker-Levy 9 impacts on Jupiter and the 2013 Chelyabinsk meteor along with the growing number of objects on the Sentry Risk Table—have drawn renewed attention to such threats.
Most deflection efforts for a large object require from a year to decades of warning, allowing time to prepare and carry out a collision avoidance project, as no known planetary defense hardware has already been developed. It has been estimated that a velocity change of just 3.5/t × 10−2 ms−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 when it was believed there was a high chance of 99942 Apophis swinging by Earth in 2029 with a 10−4 probability of passing through a 'keyhole' and returning on an impact trajectory in 2035 or 2036. It was determined that a deflection from this potential return trajectory several years before the swing by could be achieved with a velocity change on the order of 10−6 ms−1.
An impact by a 10 kilometres (6.2 mi) asteroid on the Earth has historically caused an extinction-level event due to catastrophic damage to the biosphere. 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. Impacts from objects as small as 50 metres (160 ft) in diameter, which are far more common, are historically extremely destructive regionally (see barringer crater).
Finding out the material composition of the object is also helpful before deciding which strategy is appropriate. Missions like the 2005 Deep Impact probe have provided valuable information on what to expect.
History of government mandatesEdit
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.[dated info] 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).
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 Object Survey (CINEOS), Japanese Spaceguard Association, and Asiago-DLR Asteroid Survey. Pan-STARRS completed telescope construction in 2010, and it is now actively observing.
Another project, supported by the European Union, is NEOShield, which analyses realistic options for preventing the collision of a NEO with Earth. Their aim is to provide test mission designs for feasible NEO mitigation concepts.
"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.
Orbit@home intends to provide distributed computing resources to optimize search strategy. On February 16, 2013, the project was halted due to lack of grant funding. However, on July 23, 2013, the orbit@home project was selected for funding by NASA's Near Earth Object Observation program and is to resume operations sometime in early 2014. 
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 spaceEdit
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.
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 patternEdit
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 strategiesEdit
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.
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.
Collision avoidance strategies can also be seen as either direct, or indirect and in how rapidly they transfer energy to the object. The direct methods, such as nuclear explosives, or kinetic impactors, rapidly 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 would work for short-notice, and long-notice threats, and are most effective against solid objects that can be directly pushed, but in the case of kinetic impactors, they are not very effective against large loosely aggregated rubble piles. The indirect methods, such as gravity tractors, attaching rockets or mass drivers, are much slower and require traveling to the object, time to change course up to 180 degrees to fly alongside it, and then 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 kinetic impactor 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 buckshot like fragments that could result from such an explosion would be a very daunting task, although that would be preferable than doing nothing and allowing the originally larger rubble body, (which is analogous to a shot and wax slug) to impact the Earth.
Nuclear explosive deviceEdit
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 1 mission utilizing nuclear stand off, can deflect NEOs of 100–500-metre (330–1,640 ft) diameters two years before the estimated earth impact, and larger NEOs with a five year warning.
The first mention of the concept appears to have been at a 1995 meeting at Lawrence Livermore National Laboratory (LLNL) in Calif., Edward Teller proposed to a collective of U.S. and Russian ex-Cold War weapons designers and space engineers; the use of nuclear fusion warheads in diverting the paths of extinction event class asteroids. Edward Teller suggested the creation of an orbital platform for faster missile delivery. He further suggested the need for nuclear weapons more powerful than the Tsar Bomba for this purpose. 
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.
At the 2014 NASA Innovative Advanced Concepts (NIAC) conference, Wie and his colleagues stated that, "We have the solution, using our baseline concept, to be able to mitigate the asteroid-impact threat, with any range of warning." For example, according to their computer models, with a warning time of 30 days a 1,000-foot-wide (300 m) asteroid would be neutralized by using a single HAIV, with less than 0.1 percent of the destroyed object's mass potentially striking Earth, which by comparison would be more than acceptable.
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".
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.
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 studying the preliminary design of a space mission named Don Quijote, and if flown, would be the first intentional 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[who?] argued that a strategy called 'kinetic impactor deflection' was more efficient than others.[dubious ]
Asteroid gravity tractorEdit
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[dubious ] or impossible[dubious ] 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.
"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 shepherdEdit
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 energyEdit
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.
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 engineEdit
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.
- Non-conventional rocket 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 - The DE-STAR project, proposed by researchers at the University of California, Santa Barbara, is a concept modular solar powered 1 µm, near infrared wavelength, laser array. The design calls for the array to eventually be approximately 1 km squared in size, with the modular design meaning that it could be launched in increments and assembled in space. In its early stages as a small array it could deal with smaller targets, assist solar sail probes and would also be useful in cleaning up space debris.
- Magnetic Flux Compression to magnetically brake and or capture objects that contain a high percentage of meteoric iron by deploying a wide coil of wire in its orbital path and when it passes through, Inductance creates an electromagnet solenoid to be generated.
Deflection technology concernsEdit
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.
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.
All slow energy delivery deflection technologies have inherent fine control, steering capability, making it possible to add just the right amount of energy to steer an asteroid originally destined for a mere close approach towards a specific Earth target.
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 explosion 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.
Planetary defense timelineEdit
- 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.
- 1908 Tunguska event
- 1994 Cando event
- 2002 Eastern Mediterranean event
- 2002 Vitim event
- Asteroid mining
- B612 Foundation
- Chicxulub crater
- Comet Shoemaker–Levy 9
- Cretaceous–Paleogene extinction event
- Don Quijote (spacecraft)
- Gravity tractor
- Impact events
- Lincoln Near-Earth Asteroid Research
- List of Earth-crossing minor planets
- List of impact craters on Earth
- Near-Earth object
- Palermo Technical Impact Hazard Scale
- Potentially hazardous object
- Risks to civilization, humans, and planet Earth
- Torino Scale
- "Deflecting Asteroids," by Gregory L. Matloff, IEEE Spectrum, April 2012
- Asteroid Occultation Updates
- BBC Horizon – Averting Armageddon (summary)
- British Government FAQ on Near Earth Orbit risks
- LINEAR a USAF NASA joint effort operated by M.I.T. Lincoln Laboratory.
- Near Earth Objects Directory also here.
- NASA Near-Earth Object Program
- 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
- Consolidated Risk Tables: Asteroid/Comet Connection
- Armagh University: Near Earth Object Impact Hazard
- Threats from Space: A Review of U.S. Government Efforts to Track and Mitigate Asteroids and Meteors (Part I and Part II): Hearing before the Committee on Science, Space, and Technology, House of Representatives, One Hundred Thirteenth Congress, First Session, Tuesday, March 19, 2013 and Wednesday, April 10, 2013
- 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.
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).
- 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 (based on the MIT "Project Icarus" report.)
- 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.
- 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.
- 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.
- Sliders: in "Last Days" (1995), an asteroid approaches an alternate Earth, and human civilization prepares for the apocalypse unless a nuclear weapon can be invented to deflect the asteroid.
- 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.
- 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. In the introduction of the first game a nuclear weapon is used to attempt to divert the asteroid's -named Vulcan's Hammer- path, but instead breaks it into two large pieces that strike Earth's surface.
- 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" (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.
- Hagstrum, Jonathan T. (2005). "Antipodal Hotspots and Bipolar Catastrophes: Were Oceanic Large-body Impacts the Cause?". Earth and Planetary Science Letters 236: 13–27. Bibcode:2005E&PSL.236...13H. doi:10.1016/j.epsl.2005.02.020.
- S.-Y. Park and I. M. Ross, "Two-Body Optimization for Deflecting Earth-Crossing Asteroids," Journal of Guidance, Control and Dynamics, Vol. 22, No.3, 1999, pp.415–420.
- Lu, Edward T. and Stanley G. Love. A Gravitational Tractor for Towing Asteroids, NASA, Johnson Space Center, submitted to arxiv.org September 20, 2005. (PDF document).
- "Report of the Task Force on potentially hazardous Near Earth Objects". British National Space Center. Retrieved 2008-10-21., p. 12.
- Morrison, D., 25 January 1992, The Spaceguard Survey: Report of the NASA International Near-Earth-Object Detection Workshop, NASA, Washington, D.C.
- Shoemaker, E.M., 1995, Report of the Near-Earth Objects Survey Working Group, NASA Office of Space Science, Solar System Exploration Office
- National Academy of Sciences. 2010.Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies: Final Report. Washington, DC: The National Academies Press. Available at: http://books.nap.edu/catalog.php?record_id=12842.
- Stokes, GStokes, G.; J. Evans (18–25 July 2004). "Detection and discovery of near-Earth asteroids by the linear program". 35th COSPAR Scientific Assembly. Paris, France. p. 4338. Retrieved 2007-10-23.
- "Lincoln Near-Earth Asteroid Research (LINEAR)". National Aeronautics and Space Administration. 23 October 2007.
- "The Spacewatch Project". Retrieved 2007-10-23.
- "Near-Earth Objects Search Program". National Aeronautics and Space Administration. 23 October 2007.
- "NASA Releases Near-Earth Object Search Report". National Aeronautics and Space Administration. Retrieved 2007-10-23.
- David Morrison. "NASA NEO Workshop". National Aeronautics and Space Administration.
- "orbit@home is upgrading!". Orbit.psi.edu. Retrieved 2013-10-29.
- "orbit@home is upgrading!". Orbit.psi.edu. Retrieved 2013-10-29.
- Hearing Charter: Near-Earth Objects: Status of the Survey Program and Review of NASA's 2007 Report to Congress | SpaceRef Canada – Your Daily Source of Canadian Space News
- Hildebrand, A. R.; Tedesco, E. F.; Carroll, K. A.; et al. (2008). "The Near Earth Object Surveillance Satellite (NEOSSat) Mission Will Conduct an Efficient Space-Based Asteroid Survey at Low Solar Elongations". Asteroids, Comets, Meteors. Bibcode:2008LPICo1405.8293H. Paper id 8293.
- Spears, Tom (May 2, 2008). "Canada space mission targets asteroids". Calgary Herald via Canada.com. Retrieved June 27, 2008.
- We Saw It Coming: Asteroid Monitored from Outer Space to Ground Impact Newswise, Retrieved on March 26, 2009.
- Predicting Apophis' Earth Encounters in 2029 and 2036
- "Why we have Asteroid "Scares"". Spaceguard UK. (Original Site is no longer available, see Archived Site at )
- C. D. Hall and I. M. 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.
- Ross, I. M., Park, S.-Y. and Porter, S. E., "Gravitational Effects of Earth in Optimizing Delta-V for Deflecting Earth-Crossing Asteroids," Journal of Spacecraft and Rockets, Vol. 38, No. 5, 2001, pp. 759–764.
- http://orbitalvector.com/Solar%20System/Asteroids%20And%20Comets/Redirecting%20Asteroids/REDIRECTING%20ASTEROIDS.htm "Such [rubble pile] bodies would be needed to be pushed from all points on a facing side simultaneously to avoid potential splintering. One way to achieve this is to use a powerful nuclear explosion, not on its surface, but off to its side a few kilometers, so the radiation pressure and what there is of a shockwave will give it the gentle nudge needed to alter its trajectory."
- "Physics.nist.gov". Physics.nist.gov. Retrieved 2011-11-08.
- http://orbitalvector.com/Solar%20System/Asteroids%20And%20Comets/Redirecting%20Asteroids/REDIRECTING%20ASTEROIDS.htm "In space, with no atmosphere to absorb the energy, most of a nuclear warhead's energy will manifest as radiation and heat. This radiation pressure will produce a propulsive impulse over the entire facing side of the asteroid or comet, as well as perhaps triggering some outgassing events. For most massive targets, a single such blast from even a large nuke probably wouldn't be enough, but a series of such explosions would be enough to turn all but the most massive threatening bodies.
- http://www.flightglobal.com/news/articles/nasa-plans-armageddon-spacecraft-to-blast-asteroid-215924/ NASA plans 'Armageddon' spacecraft to blast asteroid 2007. The warheads would explode at a distance of one-third of the NEO's diameter and each detonation's X and gamma rays and neutrons would turn part of the NEO's surface into an expanding plasma to generate a force to deflect the asteroid.
- Dillow, Clay (9 April 2012). "How it Would Work: Destroying an Incoming Killer Asteroid With a Nuclear Blast". Popular Science (Bonnier). Retrieved 6 January 2013.
- Jason Mick (October 17, 2013). "The mother of all bombs would sit in wait in an orbitary platform".
- http://neo.jpl.nasa.gov/neo/report2007.html Near-Earth Object Survey and Deflection Analysis of Alternatives Report to Congress March 2007
- http://www.space.com/21333-asteroid-nuke-spacecraft-mission.html Nuking Dangerous Asteroids Might Be the Best Protection, Expert Says. Includes a supercomputer simulation video provided by Los Alamos National Laboratory.
- http://orbitalvector.com/Solar%20System/Asteroids%20And%20Comets/Redirecting%20Asteroids/REDIRECTING%20ASTEROIDS.htm A small nuke is used on the surface of the asteroid or comet in order to create a large crater. The crater is then used as a crude "rocket nozzle" to channel succeeding blasts and allow the body to build up speed on a predetermined trajectory, much like a crude nuclear impulse drive.
- Mike Wall (February 14, 2014). "How Nuclear Bombs Could Save Earth from Killer Asteroids".
- Islands in Space, Dandridge M. Cole and Donald W. Cox, pp. 126–127.
- Goldstein, R. M. (1968). "Radar Observations of Icarus". Science 162 (3856): 903–4. Bibcode:1968Sci...162..903G. doi:10.1126/science.162.3856.903. PMID 17769079.
- Kleiman Louis A., Project Icarus: an MIT Student Project in Systems Engineering, Cambridge, Massachusetts : MIT Press, 1968
- "Systems Engineering: Avoiding an Asteroid", Time Magazine, June 16, 1967.
- Day, Dwayne A., "Giant bombs on giant rockets: Project Icarus", The Space Review, Monday, July 5, 2004
- 'Project Icarus
- "MIT Course precept for movie", The Tech, MIT, October 30, 1979
- http://www.space.com/21333-asteroid-nuke-spacecraft-mission.html Nuking Dangerous Asteroids Might Be the Best Protection, Expert Says. Includes a supercomputer simulation video provided by Los Alamos National Laboratory. Wie admitted that sending nuclear weapons into space would be politically controversial. However, he said there are a number of safety features that could be built into the spacecraft to prevent the nuclear warhead from detonating in the event of a launch failure.
- "Court Rejects Russian Astrologer's Lawsuit Against NASA". MosNews.com. August 11, 2005. Archived from the original on May 21, 2007. Retrieved May 11, 2009.
- Madrigal, Alexis (16 December 2009). "Saving Earth From an Asteroid Will Take Diplomats, Not Heroes". WIRED. Retrieved 17 December 2009.
- Chapman, Clark R. and Daniel D. Durda. The Comet/Asteroid Impact Hazard: A Systems Approach, Boulder, CO: Office of Space Studies, Southwest Research Institute, Space Engineering and Technology Branch, Johns Hopkins University Applied Physics Laboratory.
- "Space Based Laser. FAS.".
- --in a lecture to the Arizona Geological Society in 12-96.
- Is an asteroid capture possible/feasible?; Asteroid movement/retrieval; Asteroid relocation/mining; etceras..., Space-tech Digest #70 [bulletin board], Carnegie Mellon University, July 19–25, 1990.
- David French (October 2009). "Near-Earth Object Threat Mitigation Using a Tethered Ballast Mass". J. Aerosp. Engrg.
- Philip Lubin: A space-based array for planetary defense (video), SPIE Newsroom, 22 November 2013
- "How to Colonize an Asteroid Solenoids".
- "National Space Society, From Ad Astra, Volume 18 Number 2, Summer 2006".
- Islands in Space, Dandridge M. Cole and Donald W. Cox, pp. 7–8.
- "Astronauts push for strategies, spacecraft to prevent calamitous asteroid strike". Pittsburgh Post-Gazette. November 28, 2005. Retrieved 2008-01-18.
- "Subcommittee Questions NASA’s Plan for Detecting Hazardous Asteroids".
- Donald K. Yeomans (2007-11-08). "Testimony Before The House Committee On Science And Technology Subcommittee On Space And Aeronautics: Near-Earth Objects (NEOS) – Status Of The Survey Program And Review Of Nasa’s Report To Congress" (PDF).
- Catlalina Sky Survey website
- "Catalina Sky Survey Discovers Space Rock That Could Hit Mars". Retrieved 2007-12-22.
- "Recently Discovered Asteroid Could Hit Mars in January". Retrieved 2007-12-22.
- Leonard David. Asteroid Threat to Earth Sparks Global 'NEOShield' Project, SPACE.com, 26 January 2012.
- Bus-sized asteroid buzzes Earth today passing within 36,000 miles of our atmosphere, DailyMail online, 27 January 2012.
- Defenders Of The Planet, Off The Fence website. Retrieved April 20, 2013.
- "Trek Report: Video Report - That's a Wrap, Gang". IGN.com. 2005-05-12.
- 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