Near-Earth object detection technology began to improve around 1998, so objects being detected as of 2004 could have been missed only a decade earlier due to a lack of dedicated near-Earth astronomical surveys. As sky surveys improve, smaller and smaller asteroids are regularly being discovered. As smaller asteroids are more numerous, ever more close approaches are detected within a given distance. In 2014, scientists estimated that several dozen asteroids in the 6–12m (20–39ft) size range fly by Earth at a distance closer than the Moon every year, but only a fraction of these are actually detected.[1]
Definitions
The lists below are based on the close approach database of the Center for Near-Earth Object Studies (CNEOS), in its state as of 27February2025[update].[2] The database lists any approaches with a minimum distance less than 0.2 astronomical units (AU) from 1900 and until a century into the future which have been derived by orbit calculations. This includes some close approaches a full orbit or more before or after the object has been observed.
The distance calculated for an approach has an uncertainty, the magnitude of which depends on the amount, length in time and quality of observations used, the extrapolation time from the observations, and perturbations by other objects along the predicted orbit. The uncertainty is usually characterised by the 3-sigma uncertainty region, which is the nominal close approach distance plus or minus three times the standard deviation, and includes 99.7% of the probability distribution. For predicted close approaches in the future, if Earth is near the uncertainty region or intersects it, an impact risk is calculated.[3] Confirmed impacts, however, aren't considered close approaches and are excluded from the CNEOS close approach database. Asteroids whose detection in space led to predicted impacts on Earth are listed separately,[4] as are the hundreds of other objects that collided with Earth's atmosphere which were not discovered in advance but were observed visually or recorded by sensors designed to detect detonation of nuclear devices.[5] The CNEOS list also does not include Earth-grazers, objects that enter Earth's atmosphere at a very shallow angle and leave it again without burning up completely, but they are listed separately below. Although Earth's atmosphere thins out continuously with distance from Earth's surface, the nominal limit of space is the Kármán line, which is 100km (62mi) above sea level.
Timeline of closest approaches ever observed
The list below shows all approaches by potentially hazardous objects (objects which can approach Earth within 0.05AU) without atmospheric contact which have been the closest ever observed at some point in time, from the discovery of the first such object to the record holder, as of February2025[update].
The average distance to the Moon (or lunar distance (LD)) is 384,399km (238,854mi), which is around 30 times the diameter of the Earth.[7] The lists in this section are of close approaches in less than one LD.
Time of discovery
The bar graphs below show the time of discovery relative to the time of the closest approach for each year. The asteroids are listed in separate list articles for each year. The statistics below only include close approaches that are evidenced by observations, thus the pre-discovery close approaches are only included if the object was found by precovery.
Discovered > 1 year in advance Discovered > 7 weeks in advance Discovered > 1 week in advance Discovered up to 1 week in advance < 24 hours' warning < no warning
From the annual lists summarized in the preceding section, these are the closest known asteroids per year that approach Earth within one lunar distance. More than one asteroid per year may be listed if its geocentric distance[note 1]
The CNEOS database of close approaches lists some close approaches a full orbit or more before or after the discovery of the object, derived by orbit calculation. Until 2001 and in future years, all of these close approaches are included in the list below, but from the start of regular discoveries each year in 2001 until the current year, the list is limited to close approaches that are evidenced by observations, thus any of these pre-discovery close approaches are only included if the object was found by precovery.
Rows highlighted red indicate objects which were not discovered until after closest approach
Rows highlighted yellow indicate objects discovered less than 24 hours before closest approach
Rows left white indicate objects discovered 1–7 days before closest approach
Rows highlighted green indicate objects discovered more than one week before closest approach
Rows highlighted blue indicate objects discovered more than one year before closest approach, i.e. objects successfully cataloged on a previous orbit, rather than being detected during final approach.
*367943 Duende is listed for 2013 although it was only the second-closest that year for notability: it is the largest asteroid that was observed while it approached within the radius of the geostationary orbit, it was also predicted nearly a year in advance, and coincidentally approached just a few hours after the unrelated Chelyabinsk meteor, which was unpredicted, but injured thousands of people when it impacted.
Largest per year
Trajectory of the relatively large 2005 YU55 compared with the orbits of Earth and the Moon on 8–9 Nov 2011
From the lists in the first section, these are the largest known asteroids per year that approach Earth within one LD. (More than one asteroid per year may be listed if its size is 100m[330ft] or more.) For comparison, the 1908 Tunguska event was caused by an object about 60–190m (200–620ft) in size, while the 2013 Chelyabinsk meteor, which injured thousands of people and damaged buildings when it generated a large airburst over Russia, was estimated to be just 20m (66ft) across.
The CNEOS database of close approaches lists some close approaches a full orbit or more before or after the discovery of the object, derived by orbit calculation. For years when the largest of the objects that had an undetected close approach within 1LD was larger than the largest of the objects that were detected in real time or in precovery, both objects are listed. If there were only undetected close approaches in a year, only objects larger than 25m[82ft] (or H ≤ 25.75) are shown.
The year 2011 was notable as two asteroids with size 100m (330ft) or more approached within one lunar distance.
Extremes in relative speed
The average near-Earth asteroid, such as 2019 VF5, passes Earth at 18km/s. The average short-period comet passes Earth at 30km/s, and the average long-period comet passes Earth at 53km/s.[9] A retrograde parabolic Oort cloud comet (e=1, i=180°) could pass Earth at 72km/s when 1 AU from the Sun.
Fastest asteroid within 1 LD for each year (these asteroids have eccentric orbits)
The slowest passing speeds during close approaches are dominated by the perigees of asteroids captured by Earth as temporary satellites. This list includes close approaches that weren't observed, but the orbit was calculated with high precision.
Slowest asteroids passing within 1 LD of Earth (these asteroids have Earth-like orbits)
Goldstone radar image of asteroid 2005 YU55 taken November 7, 2011
Below are lists of the closest approaches in different size ranges, the limits of which correspond to with size limits commonly considered in impact hazard scenarios. The list includes close approaches an orbital period or more before or after the closest observations in time which were derived by orbit calculation.
The diameter of most asteroids has not been measured directly, and can only be estimated from their brightness and assumed surface reflectivity or albedo. While the measured albedo of asteroids can be as low as 6% and as high as 20%, the default estimated size for asteroids in the CNEOS databases is calculated for an albedo of 14%, which is also used for the size range limits below.[10] For objects with uncertain albedo, the CNEOS close approach database provides a possible size range, which is shown in all the lists on this page. In case other, more precise size estimates are available from other sources, the tables below show those, too, but asteroids are sorted according to the size resp. absolute magnitude in the CNEOS database.
Closest with an estimated diameter under 7 m (H > 28.5)
If an asteroid less than 7 metres (23ft) across (with an absolute magnitude greater than 28.5) impacts the Earth, it will produce spectacular but mostly harmless fireballs and meteorite falls. All of the asteroids that were destroyed in predicted impacts on Earth up to 2024 were in this size range.[4] The list below shows all close approaches within 10,000km (6,214mi) from the centre of the Earth (or about 3,600km (2,200mi) above its surface).
Closest with an estimated diameter between 7 m and 20 m (28.5 ≥ H > 26.25)
If an asteroid at the bottom of this size range, one 7 metres (23ft) across (with an absolute magnitude greater than 28.5), has average asteroid density and impacts the Earth at average meteor speed, its impact energy is about 15 kilotons TNT equivalent, or roughly equivalent to the blast energy of the Hiroshima bomb.[11] The list below shows all close approaches of objects in the range between 7 and 20 metres across within the radius of the geostationary orbit or 42,164km (26,199mi) from the centre of the Earth.
Closest with an estimated diameter between 20 m and 50 m (26.25 ≥ H > 24.25)
The bottom of this size range, 20m (66ft) corresponds to the average size of an asteroid with the smallest impact energy (1 megaton) considered for impact hazard ratings on the Torino scale.[12]20m (66ft) is also about the size of the Chelyabinsk meteor, which produced a meteor ending in an airburst briefly brighter than the Sun that injured over a thousand people and damaged thousands of buildings. The list below shows all close approaches within 100,000km (62,137mi) from the centre of the Earth.
Closest with an estimated diameter between 50 m and 140 m (24.25 ≥ H > 22.00)
NASA's Planetary Defense Coordination Office (PDCO) considers objects with a diameter of at least 50m (164ft) capable of destroying a concentrated urban area if they impact Earth.[13] The asteroid causing the Tunguska event is estimated at 50–80m (164–262ft) in diameter.[14] The list below shows all close approaches within 1LD (384,400km; 238,900mi) from the centre of the Earth.
Closest with an estimated diameter between 140 m and 1 km (22.0 ≥ H > 17.75)
In 2005, the United States Congress gave NASA an updated mandate to detect 90% of NEOs with diameters of 140m (459ft) or greater.[15] NASA's PDCO considers objects with a diameter of at least 140m (459ft) capable of creating an impact crater at least 1–2km (0.62–1.24mi) across and causing regional devastation if they impact Earth.[13] The list below shows all close approaches within 2LD (768,800km; 477,700mi) from the centre of the Earth.
Closest with an estimated diameter above 1 km (17.75 ≥ H)
The original mandate to NASA given by the United States Congress in 1998 was to detect 90% of near-Earth asteroids over 1km (0.62mi) diameter (that threaten global devastation) by 2008.[20] NASA's PDCO considers objects with a diameter of at least 1km (0.62mi) capable of creating an impact crater at least 10km (6.2mi) across and causing global devastation if they impact Earth.[13] The list below shows all close approaches within 5LD (1,922,000km; 1,194,000mi) from the centre of the Earth.
Objects which enter and then leave Earth's atmosphere, the so-called Earth-grazers, are a distinct phenomenon, inasmuch as entering the lower atmosphere can constitute an impact event rather than a close pass. Earth-grazer can also be short for a body that "grazes" the orbit of the Earth, in a different context.
Animation of the 2015 TB145 (NEO) flyby, as seen from the center of the Earth, with hourly trace circles along the path of motion
Overview
Diagram showing spacecraft and notable asteroids (past and future) between the Earth and the Moon.
Plot of orbits of known Potentially Hazardous Asteroids (size over 140m[460ft] and passing within 7.6millionkm[4.7millionmi] of Earth's orbit) as of early 2013 (alternate image)
Notes
↑ Distance from the center of Earth to the center of the object. See the NASA/JPL Solar System Dynamics Glossary: GeocentricArchived 2013-02-14 at the Wayback Machine . Earth has a radius of approximately 6,400 km.
↑ Robert Marcus; H. Jay Melosh; Gareth Collins. "Earth Impact Effects Program". Imperial College London & Purdue University. Retrieved 2013-02-04. (solution using 2600kg/m^3, 17km/s, 90 degrees)
↑ Ceplecha, Z. (March 1994). "Earth-grazing daylight fireball of August 10, 1972". Astronomy and Astrophysics. 283 (1): 287–288. Bibcode:1994A&A...283..287C. ISSN0004-6361.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
![Plot of orbits of known Potentially Hazardous Asteroids (size over 140 m [460 ft] and passing within 7.6 million km [4.7 million mi] of Earth's orbit) as of early 2013 (alternate image) Potentially Hazardous Asteroids 2013.png](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f6/Potentially_Hazardous_Asteroids_2013.png/960px-Potentially_Hazardous_Asteroids_2013.png)
