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126-638: The Planetary Defense Coordination Office ( PDCO ) is a planetary defense organization established in January 2016 within NASA 's Planetary Science Division of the Science Mission Directorate . It includes a Near Earth Observations Program which funds telescopic searches and orbit calculations. Its mission is to look for and catalogue near-Earth objects such as comets , asteroids , and potentially hazardous objects that could impact Earth, as well as help

252-485: A Long March 3B rocket and carry both an impactor and observer spacecraft. The ellipses in the diagram on the right show the predicted position of an example asteroid 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 predicted impact probability, since

378-411: 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 meters (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

504-531: A virtual impactor based on a simulated exercise conducted by the 2021 Planetary Defense Conference. In 2022, NASA spacecraft DART impacted Dimorphos , reducing the minor-planet moon's orbital period by 32 minutes. This mission constitutes the first successful attempt at asteroid deflection. In 2025, CNSA plans to launch another deflection mission to near-Earth object 2019 VL5 , a 30-meter-wide (100 ft.) asteroid, which will include both an impactor and observer spacecraft. According to expert testimony in

630-550: A 1.5-meter (59 in) f/2 telescope on the peak of Mount Lemmon , and a 68-centimeter (27 in) f/1.7 Schmidt telescope near Mount Bigelow (both in the Tucson, Arizona area). In 2005, CSS became the most prolific NEO survey surpassing Lincoln Near-Earth Asteroid Research (LINEAR) in total number of NEOs and potentially hazardous asteroids discovered each year since. CSS discovered 310 NEOs in 2005, 396 in 2006, 466 in 2007, and in 2008 564 NEOs were found. Spacewatch , which uses

756-495: A 1.6% chance of Earth impact in April 2029. As observations were collected over the next three days, the calculated chance of impact increased to as high as 2.7%, then fell back to zero, as the uncertainty zone for this close approach no longer included the Earth. There was still some uncertainty about potential impacts during later close approaches, however, as the precision of orbital calculations improved due to additional observations,

882-561: A 1.8-meter (71 in) 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), Campo Imperatore Near-Earth Object Survey (CINEOS), Japanese Spaceguard Association , and Asiago-DLR Asteroid Survey . Pan-STARRS completed telescope construction in 2010, and it

1008-520: 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

1134-594: A 2014 report by the NASA Office of Inspector General pointed out. In June 2015, NASA and National Nuclear Security Administration of the U.S. Department of Energy , which had been studying impact events on their own, signed an agreement to work in cooperation. In January 2016, NASA officially announced the establishment of the Planetary Defense Coordination Office (PDCO), appointing Lindley Johnson to lead it as Planetary Defense Officer. The PDCO

1260-616: A 90-centimeter (35 in) 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 Robert S. McMillan of the Lunar and Planetary Laboratory of the University of Arizona in Tucson, and is now being operated by McMillan. The Spacewatch project has acquired

1386-495: 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

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1512-483: A SpaceX Falcon 9 rocket from Space Launch Complex 4 East at Vandenberg Space Force Base in California. An impact by a 10-kilometer (6 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 entering the inner Solar System. The impact speed of a long-period comet would likely be several times greater than that of

1638-593: 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

1764-467: 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

1890-476: A follow-on program suggests spending US$ 250–450 million to detect 90% of all near-Earth asteroids 140 meters (460 ft) and larger by 2028. NEODyS is an online database of known NEOs. The B612 Foundation is a private nonprofit foundation with headquarters in the United States, dedicated to protecting the Earth from asteroid strikes . It is led mainly by scientists, former astronauts and engineers from

2016-522: A global catastrophe, was met by 2011. In later years, the survey effort was expanded to include smaller objects which have the potential for large-scale, though not global, damage. NEOs have low surface gravity, and many have Earth-like orbits that make them easy targets for spacecraft. As of April 2024 , five near-Earth comets and six near-Earth asteroids, one of them with a moon, have been visited by spacecraft. Samples of three have been returned to Earth, and one successful deflection test

2142-496: 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 yet been developed. It has been estimated that a velocity change of just .035 m/s ÷ t (where t is the number of years until potential impact) is needed to successfully deflect a body on a direct collision trajectory. Thus for a large number of years before impact, much smaller velocity changes are needed. For example, it

2268-540: A network of infrasound sensors designed to detect the detonation of nuclear devices. Asteroid impact prediction remains in its infancy and successfully predicted asteroid impacts are rare. The vast majority of impacts recorded by IMS are not predicted. Observed impacts aren't restricted to the surface and atmosphere of Earth. Dust-sized NEOs have impacted man-made spacecraft, including the space probe Long Duration Exposure Facility , which collected interplanetary dust in low Earth orbit for six years from 1984. Impacts on

2394-582: A new crater 40 m (130 ft) across, was the largest ever observed as of July 2019 . Through human history, the risk that any near-Earth object poses has been viewed having regard to both the culture and the technology of human society . Through history, humans have associated NEOs with changing risks, based on religious, philosophical or scientific views, as well as humanity's technological or economical capability to deal with such risks. Thus, NEOs have been seen as omens of natural disasters or wars; harmless spectacles in an unchanging universe;

2520-642: A plan to deflect the asteroid with rockets in case it was found to be on a collision course with Earth. Project Icarus received wide media coverage, and inspired the 1979 disaster movie Meteor , in which the US and the USSR join forces to blow up an Earth-bound fragment of an asteroid hit by a comet. The first astronomical program dedicated to the discovery of near-Earth asteroids was the Palomar Planet-Crossing Asteroid Survey . The link to impact hazard,

2646-498: A potential 2028 close approach 0.00031 AU (46,000 km) from the Earth, well within the orbit of the Moon, but with a large error margin allowing for a direct hit. Further data allowed a revision of the 2028 approach distance to 0.0064 AU (960,000 km), with no chance of collision. By that time, inaccurate reports of a potential impact had caused a media storm. In 1998, the movies Deep Impact and Armageddon popularised

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2772-499: A predicted impact. However, raising the alarm too soon has the danger of causing a false alarm and creating a Boy Who Cried Wolf effect if the asteroid in fact misses Earth. Various collision avoidance techniques have different trade-offs with respect to metrics such as overall performance, cost, failure risks, 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

2898-523: A restriction that applies to comets in particular, but this approach is not universal. Some authors further restrict the definition to orbits that are at least partly further than 0.983 AU away from the Sun. NEOs are thus not necessarily currently near the Earth, but they can potentially approach the Earth relatively closely. Many NEOs have complex orbits due to constant perturbation by the Earth's gravity, and some of them can temporarily change from an orbit around

3024-411: A result, the ratio of the known and the estimated total number of near-Earth asteroids larger than 1 km in diameter rose from about 20% in 1998 to 65% in 2004, 80% in 2006, and 93% in 2011. The original Spaceguard goal has thus been met, only three years late. As of March 2024 , 861 NEAs larger than 1 km have been discovered. In 2005, the original USA Spaceguard mandate was extended by

3150-600: A risk of collision with Earth, by being forwarded to scientific data-sharing networks, including NASA and academic institutions such as the Minor Planet Center. The foundation also proposes asteroid deflection of potentially dangerous NEOs by the use of gravity tractors to divert their trajectories away from Earth, a concept co-invented by the organization's CEO, physicist and former NASA astronaut Ed Lu . Orbit@home intends to provide distributed computing resources to optimize search strategy. On February 16, 2013,

3276-516: A space mission to avert the threat. REP. STEWART: ... are we technologically capable of launching something that could intercept [an asteroid]? ... DR. A'HEARN: No. If we had spacecraft plans on the books already, that would take a year ... I mean a typical small mission ... takes four years from approval to start to launch ... The ATLAS project, by contrast, aims to find impacting asteroids shortly before impact, much too late for deflection maneuvers but still in time to evacuate and otherwise prepare

3402-545: A theory that Noah's flood in the Bible was caused by a comet impact. Human perception of near-Earth asteroids as benign objects of fascination or killer objects with high risk to human society has ebbed and flowed during the short time that NEAs have been scientifically observed. The 1937 close approach of Hermes and the 1968 close approach of Icarus first raised impact concerns among scientists. Icarus earned significant public attention due to alarmist news reports. while Hermes

3528-428: A uranium tamper had been used—as each rocket vehicle's payload . The design study was later published as Project Icarus which served as the inspiration for the 1979 film Meteor . 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

3654-848: A workshop at Vulcano , Italy in 1995, and set up The Spaceguard Foundation also in Italy a year later. In 1998, the United States Congress gave NASA a mandate to detect 90% of near-earth asteroids over 1 km (0.62 mi) diameter (that threaten global devastation) by 2008. Several surveys have undertaken " Spaceguard " activities (an umbrella term), including Lincoln Near-Earth Asteroid Research (LINEAR), Spacewatch , Near-Earth Asteroid Tracking (NEAT), Lowell Observatory Near-Earth-Object Search (LONEOS), Catalina Sky Survey (CSS), Campo Imperatore Near-Earth Object Survey (CINEOS), Japanese Spaceguard Association , Asiago-DLR Asteroid Survey (ADAS) and Near-Earth Object WISE (NEOWISE). As

3780-414: Is about 0.2 m/s) and therefore move out of an Earth-impact trajectory. 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. It does not require the entire NEO to be vaporized to mitigate an impact threat. In

3906-617: Is appropriate. Missions like the 2005 Deep Impact probe and the Rosetta spacecraft, have provided valuable information on what to expect. In October 2022, a method of mapping the insides of a potentially problematic asteroid in order to determine the best area for impact was proposed. Efforts in asteroid impact prediction have concentrated on the survey method. The 1992 NASA-sponsored Near-Earth-Object Interception Workshop hosted by Los Alamos National Laboratory evaluated issues involved in intercepting celestial objects that could hit Earth. In

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4032-529: Is assessed at 1 in 34,000. The corresponding Palermo scale value of −2.05 is still the second highest for all objects on the Sentry List Table. On December 24, 2004, 370 m (1,210 ft) asteroid 99942 Apophis (at the time known only by its provisional designation 2004 MN 4 ) was assigned a 4 on the Torino scale, the highest rating given to date, as the information available at the time translated to

4158-409: Is crucial to continue studying the potential of nuclear energy in deflecting or destroying asteroids. This is because it is currently the only option for defense if scientists were not aware of the asteroid within a few months or years, depending on the asteroid's velocity. The report also notes there needs to be research done into the legal implications as well as policy implications on the topic. If

4284-478: Is detected, like all other small Solar System bodies, its positions and brightness are submitted to the (IAU's) Minor Planet Center (MPC) for cataloging. The MPC maintains separate lists of confirmed NEOs and potential NEOs. The MPC maintains a separate list for the potentially hazardous asteroids (PHAs). NEOs are also catalogued by two separate units of the Jet Propulsion Laboratory (JPL) of NASA :

4410-517: Is now actively observing. The Asteroid Terrestrial-impact Last Alert System , now in operation, conducts frequent scans of the sky with a view to later-stage detection on the collision stretch of the asteroid orbit. Those would be much too late for deflection, but still in time for evacuation and preparation of the affected Earth region. Another project, supported by the European Union , is NEOShield , which analyses realistic options for preventing

4536-428: Is now known to have, and in the study, it is assumed to be on an impact trajectory with Earth for the year 2029. Under these hypothetical conditions, the report determines that a "Cradle spacecraft" would be sufficient to deflect it from Earth impact. This conceptual spacecraft contains six B83 physics packages, each set for their maximum 1.2-megatonne yield, bundled together and lofted by an Ares V vehicle sometime in

4662-418: Is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of Earth. Asteroids as small as 20 metres (66 ft) in diameter can cause significant damage to the local environment and human populations. Larger asteroids penetrate the atmosphere to the surface of the Earth, producing craters if they impact a continent or tsunamis if they impact

4788-561: Is the first planetary defense mission of NASA. In November 2021, the DART spacecraft was launched with the goal of seeing if it could "alter an asteroid 's path, a technique that may be used to defend the planet in the future". The attempt was successful. The 2021 movie Don't Look Up is about a "planet killer" comet , in which the Planetary Defense Officer is played by Rob Morgan . PDCO chief Lindley Johnson vetted an early draft of

4914-464: The George E. Brown, Jr. Near-Earth Object Survey Act, which calls for NASA to detect 90% of NEOs with diameters of 140 m (460 ft) or greater, by 2020. In January 2020, it was estimated that less than half of these have been found, but objects of this size hit the earth only about once in 2000 years. In December 2023, the ratio of discovered NEOs with diameters of 140 m (460 ft) or greater

5040-521: The Institute for Advanced Study , Southwest Research Institute , Stanford University , NASA and the space industry . As a non-governmental organization it has conducted two lines of related research to help detect NEOs that could one day strike the Earth, and find the technological means to divert their path to avoid such collisions. The foundation's goal had been to design and build a privately financed asteroid-finding space telescope , Sentinel , which

5166-575: The Jet Propulsion Laboratory , to investigate various impact-threat scenarios in order to learn the best approach to the threat of an incoming impactor. The office would continue to use the polar orbiting infrared telescope NEOWISE , decommissioned in August 2024, to detect any potentially hazardous objects . Double Asteroid Redirection Test (DART), a joint project between NASA and the Johns Hopkins Applied Physics Laboratory ,

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5292-692: The Nubian Desert in Sudan. It was the first time that an asteroid was observed and its impact was predicted prior to its entry into the atmosphere as a meteor . 10.7 kg of meteorites were recovered after the impact. As of September 2024 , nine impacts have been predicted, all of them small bodies that produced meteor explosions, with some impacts in remote areas only detected by the Comprehensive Nuclear-Test-Ban Treaty Organization 's International Monitoring System (IMS) ,

5418-468: The Rocky Mountains from the U.S. Southwest to Canada. It passed within 58 km (36 mi) of the Earth's surface. On October 13, 1990, Earth-grazing meteoroid EN131090 was observed above Czechoslovakia and Poland, moving at 41.74 km/s (25.94 mi/s) along a 409 km (254 mi) trajectory from south to north. The closest approach to the Earth was 98.67 km (61.31 mi) above

5544-623: The Sentry Risk Table —have drawn renewed attention to such threats. The popularity of the 2021 movie Don't Look Up helped to raise awareness of the possibility of avoiding NEOs . In 2016, a NASA scientist warned that the Earth is unprepared for such an event. In April 2018, the B612 Foundation reported "It's 100 percent certain we'll be hit by a devastating asteroid, but we're not 100 percent sure when." Also in 2018, physicist Stephen Hawking , in his final book, Brief Answers to

5670-502: The United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched. In June 2018, the US National Science and Technology Council warned that the United States was unprepared for an asteroid impact event, and developed and released the "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare. Most deflection efforts for

5796-570: The WISE mission, started in September 2013 (in its second mission extension) to hunt asteroids and comets close to the orbit of Earth . 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

5922-494: The screenplay over two years before the film's 2021 release. Planetary defense While the chances of a major collision are low in the near term, it is a near- certainty that one will happen eventually unless defensive measures are taken. Astronomical events—such as the Shoemaker-Levy 9 impacts on Jupiter and the 2013 Chelyabinsk meteor , along with the growing number of near-Earth objects discovered and catalogued on

6048-473: The 1980s, with mounting evidence for the theory that the Cretaceous–Paleogene extinction event (in which the non-avian dinosaurs died out) 65 million years ago was caused by a large asteroid impact . On March 23, 1989, the 300 m (980 ft) diameter Apollo asteroid 4581 Asclepius (1989 FC) missed the Earth by 700,000 km (430,000 mi). If the asteroid had impacted it would have created

6174-400: The 2010s, each year, several mostly small NEOs pass Earth closer than the distance of the Moon. As astronomers became able to discover ever smaller and fainter and ever more numerous near-Earth objects, they began to routinely observe and catalogue close approaches. As of April 2024 , the closest approach without impact ever detected, other than meteors or fireballs that went through

6300-545: The 2020s, with each B83 being fuzed to detonate over the asteroid's surface at a height of 100 meters or 330 feet ("1/3 of the objects diameter" as its stand-off), one after the other, with hour-long intervals between each detonation. The results of this study indicated that a single employment of this option "can deflect NEOs of [100–500 meters or 300–1,600 feet diameter] two years before impact, and larger NEOs with at least five years warning". These effectiveness figures are considered to be "conservative" by its authors, and only

6426-433: The 30 m (98 ft) asteroid 367943 Duende ( 2012 DA 14 ) passed approximately 27,700 km (17,200 mi) above the surface of Earth, closer than satellites in geosynchronous orbit. The asteroid was not visible to the unaided eye. This was the first sub-lunar close passage of an object discovered during a previous passage, and was thus the first to be predicted well in advance. Some small asteroids that enter

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6552-589: The Aerospace Corporation, NASA Langley Research Center (LaRC), and SAIC (amongst others). See also Improving impact prediction . The Minor Planet Center in Cambridge, Massachusetts has been cataloging the orbits of asteroids and comets since 1947. It has recently been joined by surveys that specialize in locating the near-Earth objects (NEO), many (as of early 2007) funded by NASA's Near Earth Object program office as part of their Spaceguard program. One of

6678-528: The Big Questions , considered an asteroid collision to be the biggest threat to the planet. Several ways of avoiding an asteroid impact have been described. Nonetheless, in March 2019, scientists reported that asteroids may be much more difficult to destroy than thought earlier. In addition, an asteroid may reassemble itself due to gravity after being disrupted. In May 2021, NASA astronomers reported that 5 to 10 years of preparation may be needed to avoid

6804-651: The Earth dangerously closely and the estimated consequences that an impact would have if it occurs. Objects with both an Earth minimum orbit intersection distance (MOID) of 0.05 AU or less and an absolute magnitude of 22.0 or brighter (a rough indicator of large size) are considered PHAs. Objects that either cannot approach closer to the Earth than 0.05  AU (7,500,000 km; 4,600,000 mi), or which are fainter than H = 22.0 (about 140 m (460 ft) in diameter with assumed albedo of 14%), are not considered PHAs. The first near-Earth objects to be observed by humans were comets. Their extraterrestrial nature

6930-745: 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 revealing that the Earth is outside the error region, and the impact probability is near zero. For asteroids that are actually on track to hit Earth the predicted probability of impact continues to increase as more observations are made. This similar pattern makes it difficult to differentiate between asteroids that will only come close to Earth and those that will actually hit it. This in turn makes it difficult to decide when to raise an alarm as gaining more certainty takes time, which reduces time available to react to

7056-480: The Earth or are small enough to 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 kilometers (7,920 mi) in diameter and moves at approximately 30 km/s (19 mi/s) in its orbit, it travels

7182-451: The Earth surface, while larger objects hit the water surface, forming tsunami waves, or the solid surface, forming impact craters . The frequency of impacts of objects of various sizes is estimated on the basis of orbit simulations of NEO populations, the frequency of impact craters on the Earth and the Moon, and the frequency of close encounters. The study of impact craters indicates that impact frequency has been more or less steady for

7308-400: The Moon can be observed as flashes of light with a typical duration of a fraction of a second. The first lunar impacts were recorded during the 1999 Leonid storm. Subsequently, several continuous monitoring programs were launched. A lunar impact that was observed on September 11, 2013, lasted 8 seconds, was likely caused by an object 0.6–1.4 m (2.0–4.6 ft) in diameter, and created

7434-421: The Moon. During this approach, Icarus became the first minor planet to be observed using radar . This was the first close approach predicted years in advance, since Icarus had been discovered in 1949. The first near-Earth asteroid known to have passed Earth closer than the distance of the Moon was 1991 BA , a 5–10 m (16–33 ft) body which passed at a distance of 170,000 km (110,000 mi). By

7560-483: The Palermo Scale. Observations during the August 2022 close approach were expected to ascertain whether the asteroid will impact or miss Earth in 2095. As of April 2024 , the risk of the 2095 impact was put at 1 in 10, still the highest, with a Palermo Scale rating of −2.98. A year before the 1968 close approach of asteroid Icarus, Massachusetts Institute of Technology students launched Project Icarus, devising

7686-488: 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

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7812-436: The Sun to one around the Earth, but the term is applied flexibly for these objects, too. The orbits of some NEOs intersect that of the Earth, so they pose a collision danger. These are considered potentially hazardous objects (PHOs) if their estimated diameter is above 140 meters. PHOs include potentially hazardous asteroids (PHAs). PHAs are defined based on two parameters relating to respectively their potential to approach

7938-413: The Sun, passed Earth undetected at a distance of 0.0120 AU (4.65 LD) on June 12, 1999. In 1937, 800 m (2,600 ft) asteroid 69230 Hermes was discovered when it passed the Earth at twice the distance of the Moon . On June 14, 1968, the 1.4 km (0.87 mi) diameter asteroid 1566 Icarus passed Earth at a distance of 0.042 AU (6,300,000 km), or 16 times the distance of

8064-465: The Sun. This definition excludes larger bodies such as planets , like Venus ; natural satellites which orbit bodies other than the Sun, like Earth's Moon ; and artificial bodies orbiting the Sun. A small Solar System body can be an asteroid or a comet , thus an NEO is either a near-Earth asteroid (NEA) or a near-Earth comet (NEC). The organisations cataloging NEOs further limit their definition of NEO to objects with an orbital period under 200 years,

8190-416: 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,

8316-451: The U.S. government prepare for a potential impact event (and coordinate efforts to mitigate and deflect potential threats if one is detected). In 2005, the U.S. Congress passed the NASA Authorization Act , which, in part, tasked NASA with finding and cataloguing at least 90% of all near-Earth objects that are 140 meters or larger by 2020. However, that goal was clearly not being met by NASA's Near Earth Object Observations Program, which

8442-526: The affected Earth region. Another project, the Zwicky Transient Facility (ZTF), which surveys for objects that change their brightness rapidly, also detects asteroids passing close to Earth. Scientists involved in NEO research have also considered options for actively averting the threat if an object is found to be on a collision course with Earth. All viable methods aim to deflect rather than destroy

8568-566: The arrival time and location on Earth of its shattered surviving parts. The four-meter-diameter asteroid, called 2008 TC 3 , was initially sighted by the automated Catalina Sky Survey telescope, on October 6, 2008. Computations correctly predicted that it would impact 19 hours after discovery and 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 MN 4 ), which in 2004 temporarily had an impact probability of about 3% for

8694-522: The asteroid was removed from the Sentry Risk Table entirely in February 2008. In 2021, 2010 RF 12 was listed with the highest chance of impacting Earth, at 1 in 22 on September 5, 2095. At only 7 m (23 ft) across, the asteroid however is much too small to be considered a potentially hazardous asteroid and it poses no serious threat: the possible 2095 impact therefore rated only −3.32 on

8820-605: The atmosphere (see #Earth-grazers below), was an encounter with asteroid 2020 VT 4 on November 14, 2020. The 5–11 m (16–36 ft) NEA was detected receding from Earth; calculations showed that on the day before, it had a close approach at about 6,750 km (4,190 mi) from the Earth's centre, or about 380 km (240 mi) above its surface. On November 8, 2011, asteroid (308635) 2005 YU 55 , relatively large at about 400 m (1,300 ft) in diameter, passed within 324,930 km (201,900 mi) (0.845 lunar distances ) of Earth. On February 15, 2013,

8946-402: 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 fragmentation would be preferable to doing nothing and allowing the originally larger rubble body, which is analogous to a shot and wax slug , to impact the Earth. In Cielo simulations conducted in 2011–2012, in which

9072-562: The atomic bomb dropped on Hiroshima , approximately 15 kilotonnes of TNT) at five years, for asteroids 60 m (200 ft) across (an impact energy of 10 megatons , comparable to the Tunguska event in 1908) at 1,300 years, for asteroids 1 km (0.62 mi) across at 440 thousand years, and for asteroids 5 km (3.1 mi) across at 18 million years. Some other models estimate similar impact frequencies, while others calculate higher frequencies. For Tunguska-sized (10 megaton) impacts,

9198-550: 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. The Catalina Sky Survey (CSS) is conducted at the Steward Observatory 's Catalina Station , located near Tucson, Arizona , in the United States. It uses two telescopes,

9324-543: 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. Indirect methods, such as gravity tractors , attaching rockets or mass drivers, are much slower. They require traveling to

9450-464: 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 energetic neutrons and soft X-rays released by the detonation, which do not appreciably penetrate matter, are converted into heat upon encountering the object's surface matter, ablatively vaporizing all line of sight exposed surface areas of

9576-407: The collision of a NEO with Earth. Their aim is to provide test mission designs for feasible NEO mitigation concepts. The project particularly emphasises on two aspects. " 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

9702-488: The consequences of such an impact would be. Some NEOs have had temporarily positive Torino or Palermo scale ratings after their discovery. Since 1998, the United States, the European Union, and other nations have been scanning the sky for NEOs in an effort called Spaceguard . The initial US Congress mandate to NASA to catalog at least 90% of NEOs that are at least 1 kilometre (0.62 mi) in diameter, sufficient to cause

9828-427: 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

9954-576: The early 2020s. 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

10080-520: The estimates range from one event every 2,000–3,000 years to one event every 300 years. The second-largest observed event after the Tunguska meteor was a 1.1 megaton air blast in 1963 near the Prince Edward Islands between South Africa and Antarctica, which was detected only by infrasound sensors. However this may have been a nuclear test . The third-largest, but by far best-observed impact,

10206-544: The first asteroid with a temporarily positive rating on the Torino Scale, with about a 1 in 9,300 chance of an impact in 2049. Additional observations reduced the estimated risk to zero, and the asteroid was removed from the Sentry Risk Table in April 2002. It is now known that within the next two centuries, 2002 CU 11 will pass the Earth at a safe closest distance (perigee) of 0.00425 AU (636,000 km; 395,000 mi) on August 31, 2080. Asteroid (29075) 1950 DA

10332-468: The general public. The simple Torino scale was established at an IAU workshop in Torino in June 1999, in the wake of the public confusion about the impact risk of 1997 XF 11 . It rates the risks of impacts in the next 100 years according to impact energy and impact probability, using integer numbers between 0 and 10: The more complex Palermo Technical Impact Hazard Scale , established in 2002, compares

10458-541: 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

10584-523: The high velocity of the asteroid's vaporized mass ejecta, coupled with the object's small reduction in mass, would produce enough of a change in the object's orbit to make it miss the Earth. A Hypervelocity Asteroid Mitigation Mission for Emergency Response (HAMMER) has been proposed. While there have been no updates as of 2023 regarding the HAMMER, NASA has published its regular Planetary Defense Strategy and Action Plan for 2023. In it, NASA acknowledges that it

10710-446: The human species . The NASA commitment has resulted in the funding of a number of NEO search efforts, which made considerable progress toward the 90% goal by 2008. However the 2009 discovery of several NEOs approximately 2 to 3 kilometers in diameter (e.g. 2009 CR 2 , 2009 HC 82 , 2009 KJ , 2009 MS and 2009 OG ) demonstrated there were still large objects to be detected. United States Representative George E. Brown Jr. (D-CA)

10836-624: 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. Furthermore Near-Earth Object WISE (NEOWISE) , an extension of

10962-607: The largest explosion in recorded history, equivalent to 20,000 megatons of TNT . It attracted widespread attention because it was discovered only after the closest approach. From the 1990s, a typical frame of reference in searches for NEOs has been the scientific concept of risk . The awareness of the wider public of the impact risk rose after the observation of the impact of the fragments of Comet Shoemaker–Levy 9 into Jupiter in July 1994. In March 1998, early orbit calculations for recently discovered asteroid (35396) 1997 XF 11 showed

11088-600: The likelihood of an impact at a certain date to the probable number of impacts of a similar energy or greater until the possible impact, and takes the logarithm of this ratio. Thus, a Palermo scale rating can be any positive or negative real number, and risks of any concern are indicated by values above zero. Unlike the Torino scale, the Palermo scale is not sensitive to newly discovered small objects with an orbit known with low confidence. The National Aeronautics and Space Administration NASA maintains an automated system to evaluate

11214-613: The need for dedicated survey telescopes and options to head off an eventual impact were first discussed at a 1981 interdisciplinary conference in Snowmass, Colorado . Plans for a more comprehensive survey, named the Spaceguard Survey, were developed by NASA from 1992, under a mandate from the United States Congress . To promote the survey on an international level, the International Astronomical Union (IAU) organised

11340-451: The newly discovered comet 55P/Tempel–Tuttle has the same orbit as the Leonids. The first near-Earth asteroid to be discovered was 433 Eros in 1898. The asteroid was subject to several extensive observation campaigns, primarily because measurements of its orbit enabled a precise determination of the then imperfectly known distance of the Earth from the Sun. If a near-Earth object is near

11466-400: The notion that near-Earth objects could cause catastrophic impacts. Also at that time, a scare arose about a supposed 2003 impact of a planet called Nibiru with Earth, which persisted on the internet as the predicted impact date was moved to 2012 and then 2017. There are two schemes for the scientific classification of impact hazards from NEOs, as a way to communicate the risk of impacts to

11592-448: The object is very large but is still a loosely-held-together rubble pile, a solution is to detonate one or a series of nuclear explosive devices alongside the asteroid, at a 20-meter (66 ft) or greater stand-off height above its surface, so as not to fracture the potentially loosely-held-together object. Providing that this stand-off strategy was done far enough in advance, the force from a sufficient number of nuclear blasts would alter

11718-437: 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. Depending on the energy of the explosive device, the resulting rocket exhaust effect, created by

11844-661: The object's orbit around the Sun, rather than its current position, thus an object with such an orbit is considered an NEO even at times when it is far from making a close approach of Earth . If an NEO's orbit crosses the Earth's orbit, and the object is larger than 140 meters (460 ft) across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids , but about 0.35% are comets . There are over 34,000 known near-Earth asteroids (NEAs) and over 120 known short-period near-Earth comets (NECs). A number of solar-orbiting meteoroids were large enough to be tracked in space before striking Earth. It

11970-679: The object's trajectory enough to avoid an impact, according to computer simulations and experimental evidence from meteorites exposed to the thermal X-ray pulses of the Z-machine . In 1967, graduate students under Professor Paul Sandorff at the Massachusetts Institute of Technology were tasked with designing a method to prevent a hypothetical 18-month distant impact on Earth by the 1.4-kilometer-wide (0.87 mi) asteroid 1566 Icarus , an object that makes regular close approaches to Earth, sometimes as close as 16 lunar distances . To achieve

12096-531: The object, changing course up to 180 degrees for space rendezvous , and then taking much more time to change the asteroid's path just enough so it will miss Earth. Many NEOs are thought to be "flying rubble piles " only loosely held together by gravity, and a typical spacecraft sized kinetic-impactor deflection attempt might just break up the object or fragment it without sufficiently adjusting its course. If an asteroid breaks into fragments, any fragment larger than 35 meters (115 ft) across would not burn up in

12222-598: The part of its orbit closest to Earth's at the same time Earth is at the part of its orbit closest to the near-Earth object's orbit, the object has a close approach, or, if the orbits intersect, could even impact the Earth or its atmosphere. As of May 2019 , only 23 comets have been observed to pass within 0.1 AU (15,000,000 km; 9,300,000 mi) of Earth, including 10 which are or have been short-period comets. Two of these near-Earth comets, Halley's Comet and 73P/Schwassmann–Wachmann , have been observed during multiple close approaches. The closest observed approach

12348-407: The past 3.5 billion years, which requires a steady replenishment of the NEO population from the asteroid main belt . One impact model based on widely accepted NEO population models estimates the average time between the impact of two stony asteroids with a diameter of at least 4 m (13 ft) at about one year; for asteroids 7 m (23 ft) across (which impacts with as much energy as

12474-447: 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 was to resume operations sometime in early 2014. As of July 13, 2018, the project is offline according to its website. The Large Synoptic Survey Telescope , currently under construction, is expected to perform a comprehensive, high-resolution survey starting in

12600-446: The rate and quantity of energy delivery were sufficiently high and matched to the size of the rubble pile, such as following a tailored nuclear explosion, results indicated that any asteroid fragments, created after the pulse of energy is delivered, would not pose a threat of re- coalescing (including for those with the shape of asteroid Itokawa ) but instead would rapidly achieve escape velocity from their parent body (which for Itokawa

12726-604: The ratio to 76%. Given the rarity of impacts by objects this big mentioned above, there are probably no objects of 140 metres or larger that will hit the earth in the next few centuries. In January 2016, NASA announced the creation of the Planetary Defense Coordination Office (PDCO) to track NEOs larger than about 30–50 m (98–164 ft) in diameter and coordinate an effective threat response and mitigation effort. Survey programs aim to identify threats years in advance, giving humanity time to prepare

12852-559: The risk of impact at any date was completely eliminated by 2021. Consequently, Apophis was removed from the Sentry Risk Table. In February 2006, (144898) 2004 VD 17 , having a diameter around 300 metres, was assigned a Torino Scale rating of 2 due to a close encounter predicted for May 4, 2102. After additional observations allowed increasingly precise predictions, the Torino rating was lowered first to 1 in May 2006, then to 0 in October 2006, and

12978-454: The sea. Interest in NEOs has increased since the 1980s because of greater awareness of this risk. Asteroid impact avoidance by deflection is possible in principle, and methods of mitigation are being researched. Two scales, the simple Torino scale and the more complex Palermo scale , rate the risk presented by an identified NEO based on the probability of it impacting the Earth and on how severe

13104-461: The source of era-changing cataclysms or potentially poisonous fumes (during Earth's passage through the tail of Halley's Comet in 1910); and finally as a possible cause of a crater-forming impact that could even cause extinction of humans and other life on Earth. The potential of catastrophic impacts by near-Earth comets was recognised as soon as the first orbit calculations provided an understanding of their orbits: in 1694, Edmond Halley presented

13230-447: 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 the same year, NASA released a study where the asteroid Apophis (with a diameter of around 300 meters or 1,000 feet) was assumed to have a much lower rubble pile density (1,500 kg/m or 100 lb/cu ft) and therefore lower mass than it

13356-483: The surface. It was captured by two all-sky cameras of the European Fireball Network , which for the first time enabled geometric calculations of the orbit of such a body. When a near-Earth object impacts Earth, objects up to a few tens of metres across ordinarily explode in the upper atmosphere (usually harmlessly), with most or all of the solids vaporized and only small amounts of meteorites arriving to

13482-466: The task within the timeframe and with limited material knowledge of the asteroid's composition, a variable stand-off system was conceived. This would have used a number of modified Saturn V rockets sent on interception courses and the creation of a handful of nuclear explosive devices in the 100-megaton energy range—coincidentally, the same as the maximum yield of the Soviets' Tsar Bomba would have been if

13608-600: The thermal X-ray output of the B83 devices was considered, while neutron heating was neglected for ease of calculation purposes. Near Earth Object 34,000+ known NEOs, divided into several orbital subgroups A near-Earth object ( NEO ) is any small Solar System body orbiting the Sun whose closest approach to the Sun ( perihelion ) is less than 1.3 times the Earth–Sun distance ( astronomical unit , AU). This definition applies to

13734-532: The threat from known NEOs over the next 100 years, which generates the continuously updated Sentry Risk Table . All or nearly all of the objects are highly likely to drop off the list eventually as more observations come in, reducing the uncertainties and enabling more accurate orbital predictions. A similar table is maintained on NEODyS (Near Earth Objects Dynamic Site) by the European Space Agency (ESA). In March 2002, (163132) 2002 CU 11 became

13860-525: The threatening NEO, because the fragments would still cause widespread destruction. Deflection, which means a change in the object's orbit months to years prior to the predicted impact , also requires orders of magnitude less energy. For a given amount of energy, a greater effect on the momentum of the object can be had by causing some of it to be blasted off it, as was done in the Double Asteroid Redirection Test (see below). When an NEO

13986-403: 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: Fragmentation and delay. Fragmentation concentrates on rendering the impactor harmless by fragmenting it and scattering the fragments so that they miss

14112-419: The upper atmosphere of Earth at a shallow angle remain intact and leave the atmosphere again, continuing on a solar orbit. During the passage through the atmosphere, due to the burning of its surface, such an object can be observed as an Earth-grazing fireball . On August 10, 1972, a meteor that became known as the 1972 Great Daylight Fireball was witnessed by many people and even filmed as it moved north over

14238-418: The year 2029. Additional observations revised this probability down to zero. On September 26, 2022 DART impacted Dimorphos , reducing the minor-planet moon's orbital period by 32 minutes. This mission was the first successful attempt at asteroid deflection. In 2025, China's CNSA intends to launch a deflection mission to near-Earth object 2019 VL5 , a 30-meter wide asteroid. The mission will launch on

14364-460: Was 0.0151 AU (5.88 LD) for Lexell's Comet on July 1, 1770. After an orbit change due to a close approach of Jupiter in 1779, this object is no longer an NEC. The closest approach ever observed for a current short-period NEC is 0.0229 AU (8.92 LD) for Comet Tempel–Tuttle in 1366. Orbital calculations show that P/1999 J6 (SOHO) , a faint sungrazing comet and confirmed short-period NEC observed only during its close approaches to

14490-452: Was added to the Sentry list in April 2002 as the first object with a Palermo scale value greater than zero. The then-calculated 1 in 300 maximum chance of impact and +0.17 Palermo scale value was roughly 50% greater than the background risk of impact by all similarly large objects until 2880. After additional radar and optical observations, as of April 2024 , the probability of this impact

14616-514: Was conducted. Similar missions are in progress. Preliminary plans for commercial asteroid mining have been drafted by private startup companies, but few of these plans were pursued. Near-Earth objects (NEOs) are formally defined by the International Astronomical Union (IAU) as all small Solar System bodies with orbits around the Sun that are at least partially closer than 1.3 astronomical units (AU; Sun–Earth distance) from

14742-447: Was considered a threat because it was lost after its discovery; thus its orbit and potential for collision with Earth were not known precisely. Hermes, having a period of 2.13 years, was only re-discovered in 2003, and it is now known to be no threat for at least the next century. Scientists have recognised the threat of impacts that create craters much bigger than the impacting bodies and have indirect effects on an even wider area since

14868-510: Was estimated at 38%. The Chile-based Vera C. Rubin Observatory , which will survey the southern sky for transient events from 2025, is expected to increase the number of known asteroids by a factor of 10 to 100 and increase the ratio of known NEOs with diameters of 140 m (460 ft) or greater to at least 60%, while the NEO Surveyor satellite, to be launched in 2027, is expected to push

14994-531: Was estimated there was a high chance of 99942 Apophis swinging by Earth in 2029 with a 10 probability of returning on an impact trajectory in 2035 or 2036. It was then 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  m/s. NASA's Double Asteroid Redirection Test (DART), the world's first full-scale mission to test technology for defending Earth against potential asteroid or comet hazards, launched on

15120-478: Was given the job of cataloging and tracking potentially hazardous near-Earth objects (NEO), such as asteroids and comets , larger than 30–50 meters in diameter (compare to the 20-meter Chelyabinsk meteor that exploded over Russia in 2013) and coordinating an effective threat response and mitigation effort. It has been a part of several key NASA missions, including OSIRIS-REx , NEOWISE , and Double Asteroid Redirection Test (DART). For NEOWISE, NASA worked with

15246-560: Was lost after its 1950 discovery, since its observations over just 17 days were insufficient to precisely determine its orbit. It was rediscovered in December 2000 prior to a close approach the next year, when new observations, including radar imaging, allowed much more precise orbit calculations. It has a diameter of about a kilometer (0.6 miles), and an impact would therefore be globally catastrophic. Although this asteroid will not strike for at least 800 years and thus has no Torino scale rating, it

15372-534: 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,

15498-403: Was recognised and confirmed only after Tycho Brahe tried to measure the distance of a comet through its parallax in 1577 and the lower limit he obtained was well above the Earth diameter; the periodicity of some comets was first recognised in 1705, when Edmond Halley published his orbit calculations for the returning object now known as Halley's Comet . The 1758–1759 return of Halley's Comet

15624-612: Was the Chelyabinsk meteor of 15 February 2013. A previously unknown 20 m (66 ft) asteroid exploded above this Russian city with an equivalent blast yield of 400–500 kilotons. The calculated orbit of the pre-impact asteroid is similar to that of Apollo asteroid 2011 EO 40 , making the latter the meteor's possible parent body. On October 7, 2008, 20 hours after it was first observed and 11 hours after its trajectory has been calculated and announced, 4 m (13 ft) asteroid 2008 TC 3 blew up 37 km (23 mi) above

15750-412: Was the first comet appearance predicted. The extraterrestrial origin of meteors (shooting stars) was only recognised on the basis of the analysis of the 1833 Leonid meteor shower by astronomer Denison Olmsted . The 33-year period of the Leonids led astronomers to suspect that they originate from a comet that would today be classified as an NEO, which was confirmed in 1867, when astronomers found that

15876-489: Was to be launched in 2017–2018. However the project was cancelled in 2015. Had the Sentinel's infrared telescope been parked in an orbit similar to that of Venus , it would have helped identify threatening NEOs by cataloging 90% of those with diameters larger than 140 meters (460 ft), as well as surveying smaller Solar System objects. Data gathered by Sentinel would have helped identify asteroids and other NEOs that pose

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