Closest per year

From the list in the first 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]} is within a tenth of the lunar distance, or 0.10 LD. For comparison, since a satellite in a geostationary orbit has an altitude of about 36,000 km (22,000 mi), then its geocentric distance is 0.11 LD (approximately three times the width of the Earth).

The table shows that the years 2016 and 2017 had a total of 13 such close encounters that are known. Of these, eight were undetected until after they'd happened and only one was detected with more than 24 hours' notice. 2018 has fared better so far, with six out of the eight known close encounters being detected beforehand, albeit with less than 24 hours' notice in most cases.

This list does not include any of the hundreds of objects that collided with Earth which were not discovered in advance but were recorded by sensors designed to detect detonation of nuclear devices. Of the objects so detected, 78 had an impact energy greater than that of a 1-kiloton device (equivalent to 1,000 tons of TNT), including 11 which had an impact energy greater than that of a 10-kiloton device, i.e. comparable to the atomic bombs detonated on Hiroshima and Nagasaki in the Second World War.^[4]

  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.

A notable case is the relatively large asteroid Duende, which was predicted nearly a year in advance, coincidentally approaching just a few hours after the unrelated Chelyabinsk meteor, which was unpredicted, but injured thousands of people when it impacted.

Largest per year

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 100 m [330 ft] or more.) For comparison, the 1908 Tunguska event was caused by an object about 60–190 m (200–620 ft) 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 20 m (66 ft) across.

The table shows about 14 events in the decades 1900–2020 involving a body with an upper size estimate of 100 m (330 ft) or more making a close approach to Earth within one LD, with one (the Tunguska object) making impact.

The year 2011 was notable as two asteroids with size 100 m (330 ft) or more approached within one lunar distance.

Fastest per year

The average near-Earth asteroid, such as 2019 VF₅, passes Earth at 18 km/s. The average short-period comet passes Earth at 30 km/s, and the average long-period comet passes Earth at 53 km/s.^[10] A retrograde parabolic Oort cloud comet (e=1, i=180°) could pass Earth at 72 km/s when 1 AU from the Sun.

Objects < 50 meters

Asteroids smaller than about 50 m (160 ft).^[11]

2020 QG—Closest asteroid flyby not to hit Earth, at 2,900 km (1,800 mi); closest approach on 16 August 2020.^[12][13]

Objects > 50 meters

Asteroids larger than about 50 m (160 ft).^[11][19]

Asteroids with large uncertainty regions are not included.

* Asteroid approach did not occur during an observed apparition. Passage is calculated by integrating the equations of motion.

** Only the nominal (best-fit) orbit shows a passage this close. The uncertainty region is still somewhat large due to a short observation arc.