- Near-Earth object
A near-Earth object (NEO) is a Solar System object whose orbit brings it into close proximity with the Earth. All NEOs have a perihelion distance less than 1.3 AU. They include a few thousand near-Earth asteroids (NEAs), near-Earth comets, a number of solar-orbiting spacecraft, and meteoroids large enough to be tracked in space before striking the Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the planet. NEOs have become of increased interest since the 1980s because of increased awareness of the potential danger some of the asteroids or comets pose to the Earth, and active mitigations are being researched. A study showed that the United States and China are the nations most vulnerable to a meteor strike.
Those NEOs that are asteroids (NEA) have orbits that lie partly between 0.983 and 1.3 astronomical units away from the Sun. When an NEA is detected it is submitted to the Harvard Minor Planet Center for cataloging. Some near-Earth asteroids' orbits intersect that of Earth's so they pose a collision danger. The United States, European Union and other nations are currently scanning for NEOs in an effort called Spaceguard.
In the United States, NASA has a congressional mandate to catalogue all NEOs that are at least 1 kilometer wide, as the impact of such an object would be expected to produce severe to catastrophic effects. As of October 2008[update], 982 of these mandated NEOs have been detected. It was estimated in 2006 that 20% of the mandated objects have not yet been found. Efforts are under way to use an existing telescope in Australia to cover the ~30% of the sky that has not yet been surveyed.
Potentially hazardous objects (PHOs) are currently defined based on parameters that measure the object's potential to make threatening close approaches to the Earth. Mostly objects with an Earth minimum orbit intersection distance (MOID) of 0.05 AU or less and an absolute magnitude (H) of 22.0 or less (a rough indicator of large size) are considered PHOs. Objects that cannot approach closer to the Earth (i.e. MOID) than 0.05 AU (7,500,000 km; 4,600,000 mi), or are smaller than about 150 m (500 ft) in diameter (i.e. H = 22.0 with assumed albedo of 13%), are not considered PHOs. The NASA Near Earth Object Catalog also includes the approach distances of asteroids and comets measured in Lunar Distances, and this usage has become the more usual unit of measure used by the press and mainstream media in discussing these objects.
Some NEOs are of high interest because they can be physically explored with lower mission velocity even than the Moon, due to their combination of low velocity with respect to Earth (ΔV) and small gravity, so they may present interesting scientific opportunities both for direct geochemical and astronomical investigation, and as potentially economical sources of extraterrestrial materials for human exploitation. This makes them an attractive target for exploration. As of 2008, two near-Earth objects have been visited by spacecraft: 433 Eros, by NASA's Near Earth Asteroid Rendezvous probe, and 25143 Itokawa, by the JAXA Hayabusa mission.
- 1 Risk scales
- 2 Number and classification of near-Earth objects
- 3 Impact rate
- 4 Historic impacts
- 5 Close approaches
- 6 Future impacts
- 7 Projects to minimize the threat
- 8 See also
- 9 References
- 10 External links
There are two schemes for classification of impact hazards:
The annual background frequency used in the Palermo scale for impacts of energy greater than E megatonnes is estimated as:
For instance, this formula implies that the expected value of the time from now until the next impact greater than 1 megatonne is 33 years, and that when it occurs, there is a 50% chance that it will be above 2.4 megatonnes. This formula is only valid over a certain range of E.
However, another paper published in 2002 – the same year as the paper on which the Palermo scale is based – found a power law with different constants:
This formula gives considerably lower rates for a given E. For instance, it gives the rate for bolides of 10 megatonnes or more (like the Tunguska explosion) as 1 per thousand years, rather than 1 per 210 years as in the Palermo formula. However, the authors give a rather large uncertainty (once in 400 to 1800 years for 10 megatonnes), due in part to uncertainties in determining the energies of the atmospheric impacts that they used in their determination.
Highly rated risks
On 25 December 2004, minor planet 2004 MN4 (later named 99942 Apophis) was assigned a 4 on the Torino scale, the highest rating so far. On 27 December 2004, there was a 2.7% chance of Earth impact on 13 April 2029. However, on 28 December 2004, the risk of impact dropped to zero for 2029, but, due to a resonant return possibility the Torino rating for an April 2036 impact rose to 4 in early 2005, but by October 2009 the Torino rating was 0 (zero). The Palermo rating (October 2009) is −3.08.
As of 12 September 2011, the only known NEO with a Palermo scale value greater than zero is (29075) 1950 DA, which is predicted to pass very close to or collide with the Earth (p ≤ 0.003) in the year 2880. Depending on the orientation of its axis of rotation, it will either miss the Earth by tens of millions of kilometers, or have a 1 in 300 chance of hitting the Earth. However, humanity has over 800 years to refine its estimates of the orbit of (29075) 1950 DA, and to deflect it, if necessary.
List of current threats
NASA maintains a continuously updated web page of the most significant NEO threats in the next 100 years. All or nearly all of the items on this page are highly likely to drop off the list eventually as more data comes in, enabling more accurate predictions. (The page does not include 1950 DA, because that will not strike for at least 800 years.)
Number and classification of near-Earth objects
While orbiting the Sun, most potential impactors can be classified as meteoroids, asteroids, or comets depending on size and composition. Asteroids can also be members of an asteroid family, and comets can leave debris in their orbits.
As of April 2011[update], 7,954 NEOs have been discovered: 87 near-Earth comets and 7,867 near-Earth Asteroids. Of those there are 647 Aten asteroids, 2,920 Amor asteroids, and 4,289 Apollo asteroids. There are 1,215 NEOs that are classified as potentially hazardous asteroids (PHAs). Currently, 148 PHAs and 824 NEAs have an absolute magnitude of 17.75 or brighter, which roughly corresponds to at least 1 km in size.
As of April 2011[update], there are 368 NEAs on the impact risk page at the NASA website. A significant number of these NEAs – 215 as of May 2010[update] – are equal to or smaller than 50 meters in diameter and none of the listed objects are placed even in the "yellow zone" (Torino Scale 2), meaning that none warrant the attention of general public. As of November 2011[update], only asteroids 2007 VK184 and 2011 AG5 are listed as having a Torino Scale of 1.
Near-Earth meteoroids are objects with orbits in the vicinity of Earth's orbit having a diameter less than 50 meters.
These are objects of 50 meters or more in diameter in a near-Earth orbit without the tail or coma of a comet. As of May 2010[update], 7,075 near-Earth asteroids are known, ranging in size up to ~32 kilometers (1036 Ganymed). The number of near-Earth asteroids over one kilometer in diameter is estimated to be 500–1,000. The composition of near-Earth asteroids is comparable to that of asteroids from the asteroid belt, reflecting a variety of asteroid spectral types.
NEAs survive in their orbits for just a few million years. They are eventually eliminated by planetary perturbations which cause ejection from the Solar System or a collision with the Sun or a planet. With orbital lifetimes short compared to the age of the Solar System, new asteroids must be constantly moved into near-Earth orbits to explain the observed asteroids. The accepted origin of these asteroids is that asteroid-belt asteroids are moved into the inner Solar System through orbital resonances with Jupiter. The interaction with Jupiter through the resonance perturbs the asteroid's orbit and it comes into the inner Solar System. The asteroid belt has gaps, known as Kirkwood gaps, where these resonances occur as the asteroids in these resonances have been moved onto other orbits. New asteroids migrate into these resonances, due to the Yarkovsky effect that provides a continuing supply of near-Earth asteroids.
A small number of NEOs are extinct comets that have lost their volatile surface materials, although having a faint or intermittent comet-like tail does not necessarily result in a classification as a near-Earth comet, making the boundaries somewhat fuzzy. The rest of the near-Earth asteroids are driven out of the asteroid belt by gravitational interactions with Jupiter.
There are three families of near-Earth asteroids:
- The Atens, which have average orbital radii less than one AU and aphelia of more than Earth's perihelion (0.983 AU), placing them usually inside the orbit of Earth.
- The Apollos, which have average orbital radii more than that of the Earth and perihelia less than Earth's aphelion (1.017 AU).
- The Amors, which have average orbital radii in between the orbits of Earth and Mars and perihelia slightly outside Earth's orbit (1.017–1.3 AU). Amors often cross the orbit of Mars, but they do not cross the orbit of Earth.
Many Atens and all Apollos have orbits that cross (though not necessarily intersect) that of the Earth, so they are a threat to impact the Earth on their current orbits. Amors do not cross the Earth's orbit and are not immediate impact threats. However, their orbits may evolve into Earth-crossing orbits in the future.
As of May 2010[update], 84 near-Earth comets have been discovered. Although no impact of a comet in Earth´s history has been conclusively confirmed, the Tunguska event may have been caused by a fragment of Comet Encke. Cometary fragmenting may also be responsible for some impacts from near-Earth objects.
Objects with diameters of 5-10 m impact the Earth's atmosphere approximately once per year, with as much energy as the atomic bomb dropped on Hiroshima, approximately 15 kilotonnes of TNT. These ordinarily explode in the upper atmosphere, and most or all of the solids are vaporized. Every 2000–3000 years NEAs produce explosions comparable to the one observed at Tunguska in 1908. Objects with a diameter of one kilometer hit the Earth an average of twice every million year interval. Large collisions with five kilometer objects happen approximately once every ten million years.
The rate of impacts of objects of at least 1 km in diameter is estimated as 2 per million years. Assuming that this rate will continue for the next billion years, there exist at least 2,000 objects of diameter greater than 1 km that will eventually hit Earth. However, most of these are not yet considered potentially hazardous objects because they are currently orbiting between Mars and Jupiter. Eventually they will change orbits and become NEOs. Objects spend on average a few million years as NEOs before hitting the Sun, being ejected from the Solar System, or (for a small proportion) hitting a planet.
The general acceptance of the Alvarez hypothesis, explaining the Cretaceous–Tertiary extinction event as the result of a large object impact event, raised the awareness of the possibility of future Earth impacts with other objects that cross the Earth's orbit.
1908 Tunguska event
It is now commonly believed that on 30 June 1908 a stony asteroid exploded over Tunguska with the energy of the explosion of 10 megatons of TNT. The explosion occurred at a height of 8.5 kilometers. The object that caused the explosion has been estimated to have had a diameter of 45–70 meters.
1979 Vela Incident
A 22 September 1979 event recorded as occurring near the junction of the South Atlantic and the Indian Ocean was possibly a low-yield nuclear test, but was also initially thought to have been caused by the possible impact of an extraterrestrial object. The event, which became known as the Vela Incident, was identified by a U.S. Vela defence satellite in Earth orbit. The event alarm triggered multi-year investigations by several organizations which could not conclusively determine if the explosion was of nuclear or non-nuclear origin.
2002 Eastern Mediterranean event
On 6 June 2002 an object with an estimated diameter of 10 meters collided with Earth. The collision occurred over the Mediterranean Sea, between Greece and Libya, at approximately 34°N 21°E and the object exploded in mid-air. The energy released was estimated (from infrasound measurements) to be equivalent to 26 kilotons of TNT, comparable to a small nuclear weapon.
2008 Sudan event
On 6 October 2008, scientists calculated that a small near-Earth asteroid, 2008 TC3, just sighted that night, would impact the Earth on 7 October over Sudan, at 0246 UTC, 5:46 local time. The asteroid arrived as predicted. This is the first time that an asteroid impact on Earth has been accurately predicted. However, no reports of the actual impact have so far been published since it occurred in a very sparsely populated area.
2009 Indonesia event
A large fireball was observed in the skies near Bone, Indonesia on October 8, 2009. This was thought to be caused by an asteroid approximately 10 meters in diameter. The fireball contained an estimated energy of 50 kilotons of TNT, or about twice the Nagasaki atomic bomb. No injuries were reported.
On August 10, 1972 a meteor that became known as The Great Daylight 1972 Fireball was witnessed by many people moving north over the Rocky Mountains from the U.S. Southwest to Canada. It was an Earth-grazing meteoroid that passed within 57 kilometers (about 34 miles) of the Earth's surface. It was filmed by a tourist at the Grand Teton National Park in Wyoming with an 8-millimeter color movie camera.
On March 23, 1989 the 300-meter (1,000-foot) diameter Apollo asteroid 4581 Asclepius (1989 FC) missed the Earth by 700,000 kilometers (430,000 mi) passing through the exact position where the Earth was only 6 hours before. If the asteroid had impacted it would have created the largest explosion in recorded history, twelve times more powerful than the Tsar Bomba, the most powerful nuclear bomb ever exploded by man. It attracted widespread attention as early calculations had its passage being as close as 64,000 km (40,000 mi) from the Earth, with large uncertainties that allowed for the possibility of it striking the Earth.
On March 18, 2004, LINEAR announced a 30-meter asteroid, 2004 FH, which would pass the Earth that day at only 42,600 km (26,500 mi), about one-tenth the distance to the Moon, and the closest miss ever noticed. They estimated that similar-sized asteroids come as close about every two years.
On March 31, 2004, two weeks after 2004 FH, meteoroid 2004 FU162 set a new record for closest recorded approach, passing Earth only 6,500 km (4,000 mi) away (about one-sixtieth of the distance to the Moon). Because it was very small (6 meters/20 feet), FU162 was detected only hours before its closest approach. If it had collided with Earth, it probably would have harmlessly disintegrated in the atmosphere.
On March 2, 2009, near-Earth asteroid 2009 DD45 flew by Earth at about 13:40 UT. The estimated distance from Earth was 72,000 km (45,000 mi), approximately twice the height of a geostationary communications satellite. The estimated size of the space rock was about 35 meters (115 feet) wide.
On January 13, 2010 at 12:46 UT, near-Earth asteroid 2010 AL30 passed at about 122,000 km (76,000 mi). It was approximately 10–15 m (33–49 ft) wide. If 2010 AL30 had entered the Earth's atmosphere, it would have created an air burst equivalent to between 50 kT and 100 kT (kilotons of TNT). The Hiroshima "Little Boy" atom bomb had a yield between 13-18kT.
On June 28, 2011 an asteroid designated 2011 MD, estimated at 5–20 m (16–66 ft) in diameter, passed within 20,000 km (12,000 mi) of the Earth, passing over the Atlantic Ocean.
On November 8, 2011 2005 YU55 (at about 400m diameter) passed within 324,600 km (201,700 mi) (0.85 lunar distances) from Earth.
Although there have been a few false alarms, a number of objects have been known to be threats to the Earth. (89959) 2002 NT7 was the first asteroid with a positive rating on the Palermo Technical Impact Hazard Scale, with approximately one in a million on a potential impact date of February 1, 2019. It is now known that on January 13, 2019, 2002 NT7 will safely pass 0.4078 AU (61,010,000 km; 37,910,000 mi) from the Earth.
Asteroid (29075) 1950 DA was lost after its discovery in 1950 since not enough observations were made to allow plotting of its orbit, and then rediscovered on December 31, 2000. The chance it will impact Earth on March 16, 2880 during its close approach has been estimated as 1 in 300. This chance of impact for such a large object is roughly 50% greater than that for all other such objects combined between now and 2880. It has a diameter of about a kilometer (0.6 miles).
Projects to minimize the threat
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, Campo Imperatore Near-Earth Objects Survey (CINEOS), Japanese Spaceguard Association, and Asiago-DLR Asteroid Survey. In 1998, the United States Congress mandated the Spaceguard Survey – detection of 90% of near-earth asteroids over 1 km diameter (which threaten global devastation) by 2008. This could be extended by the George E. Brown, Jr. Near-Earth Object Survey Act, which calls for NASA to detect 90 percent of NEOs with diameters of 140 meters or greater by 2020.[Need quotation to verify][Full citation needed]
As of 2011, 911 of the largest (>1 km diameter) near-Earth asteroids have been found, with some 70 still missing.
- List of Earth-crossing minor planets
- 6Q0B44E, in Earth orbit with a period of 80 days
- J002E3, probably the 3rd stage of Apollo 12
- BRAMS (Belgian RAdio Meteor Stations); study of meteor population 
- Co-orbital configuration
- Mission Marco Polo
- Space debris
- 2010 SO16
- Asteroid mining
- Potentially hazardous object
- ^ Glossary of Astronomical Terms
- ^ a b Richard Monastersky (March 1, 1997). "The Call of Catastrophes". Science News Online. http://www.sciencenews.org/pages/sn_arc97/75th/rm_essay.htm. Retrieved 2007-10-23.
- ^ Krajik, K. (2007) Killer Space Rocks. Popular Science magazine, September. pg 72-73.
- ^ a b c d e A. Morbidelli, W. F. Bottke Jr., Ch. Froeschlé, P. Michel (January 2002). W. F. Bottke Jr., A. Cellino, P. Paolicchi, and R. P. Binzel. ed. "Origin and Evolution of Near-Earth Objects" (PDF). Asteroids III (University of Arizona Press): 409–422. http://www.boulder.swri.edu/~bottke/Reprints/Morbidelli-etal_2002_AstIII_NEOs.pdf.
- ^ Clark R. Chapman (May 2004). "The hazard of near-Earth asteroid impacts on earth". Earth and Planetary Science Letters 222 (1): 1–15. Bibcode 2004E&PSL.222....1C. doi:10.1016/j.epsl.2004.03.004.
- ^ a b Shiga, David (2006-06-27). "New telescope will hunt dangerous asteroids". New Scientist. http://www.newscientist.com/article/dn9403. Retrieved 2008-11-15.
- ^ "Unusual Minor Planets". Minor Planet Center. 2008-10-21. http://www.minorplanetcenter.org/iau/lists/Unusual.html. Retrieved 2010-10-25.
- ^ "Potentially Hazard Asteroids". NASA/JPL Near-Earth Object Program Office. http://neo.jpl.nasa.gov/neo/pha.html. Retrieved 2011-05-05.
- ^ http://neo.jpl.nasa.gov/neo/groups.html
- ^ NEO Earth Close Approaches at NASA/JPL Near-Earth Object Program Office
- ^ Dan Vergano (February 2, 2007). "Near-Earth asteroids could be 'steppingstones to Mars'". USA Today. http://www.usatoday.com/tech/science/space/2007-02-12-asteroid_x.htm. Retrieved 2007-10-22.
- ^ Rui Xu, Pingyuan Cui, Dong Qiao and Enjie Luan (18 March 2007). "Design and optimization of trajectory to Near-Earth asteroid for sample return mission using gravity assists". Advances in Space Research 40 (2): 200–225. Bibcode 2007AdSpR..40..220X. doi:10.1016/j.asr.2007.03.025.
- ^ Donald Savage and Michael Buckley (January 31, 2001). "NEAR Mission Completes Main Task, Now Will Go Where No Spacecraft Has Gone Before". National Aeronautics and Space Administration. http://nssdc.gsfc.nasa.gov/planetary/news/near_descent_pr_20010131.html. Retrieved 2007-10-22.
- ^ Don Yeomans (August 11, 2005). "Hayabusa's Contributions Toward Understanding the Earth's Neighborhood". National Aeronautics and Space Administration. http://neo.jpl.nasa.gov/missions/hayabusa.html. Retrieved 2007-10-22.
- ^ "The flux of small near-Earth objects colliding with the Earth" by P. Brown et al., Nature, 420, pp. 294–6, November 2002.
- ^ a b c "Current Impact Risks". http://neo.jpl.nasa.gov/risk. Retrieved 2010-05-28.
- ^ NASA's Near Earth Object Program
- ^ a b c NEO Discovery Statistics
- ^ The Torino Impact Hazard Scale
- ^ Dr. David R. Williams (September 13, 2006). "Near Earth Object Fact Sheet". National Aeronautics and Space Administration. http://nssdc.gsfc.nasa.gov/planetary/factsheet/neofact.html. Retrieved 2007-10-22.
- ^ Jane Platt (January 12, 2000). "Asteroid Population Count Slashed". National Aeronautics and Space Administration. http://www.jpl.nasa.gov/releases/2000/neat.html. Retrieved 2007-10-22.
- ^ David Rabinowitz, Eleanor Helin, Kenneth Lawrence and Steven Pravdo (13 January 2000). "A reduced estimate of the number of kilometer-sized near-Earth asteroids". Nature 403 (6766): 165–166. Bibcode 2000Natur.403..165R. doi:10.1038/35003128. PMID 10646594. http://www.nature.com/nature/journal/v403/n6766/full/403165a0.html. Retrieved 2007-10-22.
- ^ D.F. Lupishko and T.A. Lupishko (May 2001). "On the Origins of Earth-Approaching Asteroids". Solar System Research 35 (3): 227–233. Bibcode 2001SoSyR..35..227L. doi:10.1023/A:1010431023010.
- ^ A. Morbidelli, D. Vokrouhlický (May 2003). "The Yarkovsky-driven origin of near-Earth asteroids". Icarus 163 (1): 120–134. Bibcode 2003Icar..163..120M. doi:10.1016/S0019-1035(03)00047-2.
- ^ D.F. Lupishko, M. di Martino and T.A. Lupishko (September 2000). "What the physical properties of near-Earth asteroids tell us about sources of their origin?". Kinematika i Fizika Nebesnykh Tel Supplimen 3 (3): 213–216. Bibcode 2000KFNTS...3..213L.
- ^ The distance from the Earth to the Sun
- ^ Ron Cowen (February 20, 1993). "Near-Earth asteroids: class consciousness – new asteroids identified". Science News. http://findarticles.com/p/articles/mi_m1200/is_n8_v143/ai_13526583. Retrieved 2007-10-23.
- ^ "The Tunguska object – A fragment of Comet Encke". Astronomical Institutes of Czechoslovakia. http://adsabs.harvard.edu/abs/1978BAICz..29..129K. Retrieved 2007-10-15.
- ^ Clark R. Chapman & David Morrison (6 January 1994). "Impacts on the Earth by asteroids and comets: assessing the hazard". Nature 367 (6458): 33–40. Bibcode 1994Natur.367...33C. doi:10.1038/367033a0.
- ^ EARTH IN THE COSMIC SHOOTING GALLERY, D. J. Asher et al. page 2
- ^ Morbidelli, A., W. F. Bottke, Ch. Froeschle, and P. Michel. 2002. Origin and evolution of near-Earth objects. In Asteroids III, (W. F. Bottke, A. Cellino, P. Paolicchi, R. Binzel, Eds). U. Arizona Press, 409-422.
- ^ Christopher F. Chyba, Paul J. Thomas & Kevin J. Zahnle (January 7, 1993). "The 1908 Tunguska explosion: atmospheric disruption of a stony asteroid". Nature 361 (6407): 40–44. Bibcode 1993Natur.361...40C. doi:10.1038/361040a0.
- ^ P. Brown, R.E. Spalding, D.O. ReVelle, E. Tagliaferri and S.P. Worden (21 November 2002). "The flux of small near-Earth objects colliding with the Earth" (PDF). Nature 420 (6913): 294–296. doi:10.1038/nature01238. PMID 12447433. http://www.astro.uwo.ca/~pbrown/documents/flux-final.pdf. Retrieved 2007-10-23.
- ^ Don Yeomans (October 6, 2008). "Small Asteroid Predicted to Cause Brilliant Fireball over Northern Sudan". NASA/JPL Near-Earth Object Program Office. http://neo.jpl.nasa.gov/news/news159.html. Retrieved 2008-10-09.
- ^ Richard A. Kerr (6 October 2008). "FLASH! Meteor to Explode Tonight". ScienceNOW Daily News. http://sciencenow.sciencemag.org/cgi/content/full/2008/1006/2. Retrieved 2008-10-09.
- ^ Don Yeomans (October 7, 2008). "Impact of Asteroid 2008 TC3 Confirmed". NASA/JPL Near-Earth Object Program Office. http://neo.jpl.nasa.gov/news/news160.html. Retrieved 2008-10-09.
- ^ Richard A. Kerr (8 October 2008). "Asteroid Watchers Score a Hit". ScienceNOW Daily News. http://sciencenow.sciencemag.org/cgi/content/full/2008/1008/1. Retrieved 2008-10-09.
- ^ Little Asteroid Makes a Big Splash Sky and Telescope, October 9, 2008.
- ^ http://neo.jpl.nasa.gov/news/news165.html
- ^ Grand Teton Meteor Video, Youtube
- ^ Brian G. Marsden (1998-03-29). "HOW THE ASTEROID STORY HIT: AN ASTRONOMER REVEALS HOW A DISCOVERY SPUN OUT OF CONTROL". The Boston Globe. http://www.cfa.harvard.edu/iau/pressinfo/1997XF11Globe.html. Retrieved 2007-10-23.
- ^ Steven R. Chesley and Paul W. Chodas (March 17, 2004). "Recently Discovered Near-Earth Asteroid Makes Record-breaking Approach to Earth". National Aeronautics and Space Administration. http://neo.jpl.nasa.gov/news/news142.html. Retrieved 2007-10-23.
- ^ Yahoo News – 20090302 – Asteroid Flies Past Earth
- ^ Small Asteroid 2010 AL30 Will Fly Past The Earth. NASA/JPL Near-Earth Object Program, January 12, 2010.
- ^ Near-Earth Object 2010 AL30. NASA Earth Science Picture of the Day March 06, 2010.
- ^ "Asteroid soars over Atlantic Ocean". Australian Broadcasting Corporation. June 28, 2011. http://www.abc.net.au/news/stories/2011/06/28/3255543.htm. Retrieved 2011-07-03.
- ^ "JPL Close-Approach Data: 89959 (2002 NT7)". 2011-09-12 last obs (arc=57 years). http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2002NT7;cad=1#cad. Retrieved 2011-11-04.
- ^ Giorgini, J. D.; Ostro, S. J.; Benner, L. A. M.; Chodas, P. W.; Chesley, S. R.; Hudson, R. S.; Nolan, M. C.; Klemola, A. R. et al. (April 5, 2002). "Asteroid 1950 DA's Encounter with Earth in 2880: Physical Limits of Collision Probability Prediction" (PDF). Science 296 (5565): 132–136. Bibcode 2002Sci...296..132G. doi:10.1126/science.1068191. PMID 11935024. http://neo.jpl.nasa.gov/1950da/1950da.pdf. Retrieved January 11, 2010.
- ^ National Academy of Sciences Jan. 23, 2010 Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies: Final Report. Washington, DC: The National Academies Press. Book available at: http://books.nap.edu/catalog.php?record_id=12842.
- ^ http://www.nasa.gov/mission_pages/WISE/multimedia/gallery/neowise/pia14734.html
- ^ Belgian RAdio Meteor Stations
- Interactive Earth damage impact calculator from NEO
- The Jet Propulsion Laboratory's NEO website / NEO Earth Close Approaches
- TECA Table of next close approaches to the Earth
- SAEL Small Asteroids Encounter List
- MBPL Minor Body Priority List
- Spaceguard UK
- House Holds Hearing On NEO Threat
- The UK NEO Information Centre
- Earth in the Cosmic Shooting Gallery Paper published 2005
- Near Earth Asteroids Astronomy Cast episode #29, includes full transcript.
- Upcoming Close Approaches (<0.10 A.U.) of Near-Earth Objects to Earth
- Catalogue of the Solar System Small Bodies Orbital Evolution
- NASA Space Telescope Finds Fewer Asteroids Near Earth (09.29.11)
Small Solar System bodies Minor planets Comets Meteoroids Lists / categories
Wikimedia Foundation. 2010.
Look at other dictionaries:
near-earth object — noun A large celestial object, such as an asteroid, whose orbit may possibly bring it into collision with the earth (abbrev NEO) • • • Main Entry: ↑near … Useful english dictionary
Near-Earth object — Erdnahe Objekte (engl. Near Earth object; NEO), auch Erdbahnkreuzer, sind Asteroiden, Kometen und große Meteoroiden, welche bei ihrem Umlauf um die Sonne die Erdbahn kreuzen und deshalb eine Kollisionsgefahr bergen. Um dieser Gefahr begegnen zu… … Deutsch Wikipedia
Near Earth Object — Erdnahe Objekte (engl. Near Earth object; NEO), auch Erdbahnkreuzer, sind Asteroiden, Kometen und große Meteoroiden, welche bei ihrem Umlauf um die Sonne die Erdbahn kreuzen und deshalb eine Kollisionsgefahr bergen. Um dieser Gefahr begegnen zu… … Deutsch Wikipedia
Near earth object — Objet géocroiseur En astronomie, les objets géocroiseurs sont des corps célestes susceptibles à un moment ou à un autre de passer à proximité de la Terre. Ils sont souvent désignés par l acronyme NEO, de l anglais Near Earth Object : objet… … Wikipédia en Français
near-Earth object — noun An asteroid, comet or large meteoroid whose orbit intersects Earths orbit, especially those which pose a collision danger … Wiktionary
Near Earth Object Program — est un programme du JPL destiné, comme NEODyS ( Near Earth Objects Dynamic Site ), à détecter et classifier les objets potentiellement dangereux s approchant de la Terre et d assurer une communication plus facile avec le grand public quand de… … Wikipédia en Français
Near Earth Object Surveillance Satellite — The Near Earth Object Surveillance Satellite (NEOSSat) is a Canadian microsatellite using a 15 cm aperture f/5.88 Maksutov telescope similar to that on the MOST spacecraft, 3 axis stabilized with pointing stability of 2 arcseconds in a 100… … Wikipedia
Campo Imperatore Near Earth Object Survey — The CINEOS program (Campo Imperatore Near Earth Object Survey), started in 2001, is dedicated to the discovery and follow up of Near Earth objects, namely asteroids and comets which periodically approach or intersect the Earth s orbit.In… … Wikipedia
Lowell observatory near-earth-object search — (LONEOS) est un programme dirigé par la NASA et l observatoire Lowell pour découvrir des objets géocroiseurs. Le système LONEOS a commencé les observations en décembre 1997. Le principal chercheur est Ted Bowell. LONEOS utilise un système avec… … Wikipédia en Français
Lowell Observatory Near-Earth-Object Search — (LONEOS) was a project designed to discover asteroids and comets that orbit near the Earth. The project, funded by NASA, was directed by Dr. Ted Bowell of Lowell Observatory in Flagstaff, Arizona. The LONEOS project began in 1993 and ran until… … Wikipedia