List of asteroid close approaches to Earth in 2021

Asteroids which came closer to Earth than the Moon in 2021 by time of discovery

After closest approach: 70 (44.3%)   < 24 hours before: 33 (20.9%)   up to 7 days before: 54 (34.2%)   > one week before: 0 (0.0%)   > 7 weeks before: 0 (0.0%)   > one year before: 1 (0.6%) Other years 2019, 2020, 2021, 2022, 2023

Asteroids which came closer to Earth than the Moon in 2021 by discoverer

G96 Mt. Lemmon Survey: 53 (33.8%)   F51 Pan-STARRS 1, Haleakala: 17 (10.8%)   T05 ATLAS-HKO, Haleakala: 13 (8.3%)   381 Tokyo-Kiso: 13 (8.3%)   703 Catalina Sky Survey: 12 (7.6%)   T08 ATLAS-MLO, Mauna Loa: 12 (7.6%)   I41 ZTF, Palomar Mountain: 10 (6.4%)   P07 SST, HEH Station: 9 (5.7%)   K88 GINOP-KHK, Piszkesteto: 7 (4.5%)   W94 MAP, San Pedro de Atacama: 5 (3.2%)   F52 Pan-STARRS 2, Haleakala: 4 (2.5%)   V00 Kitt Peak-Bok: 2 (1.3%)

Prediction accuracy for asteroids of magnitude 27 or larger predicted to pass within 1 lunar distance of Earth in 2021[note 1]

Unpredicted: 11 (91.7%)   Predicted but not observed: 1 (8.3%)   Observed but details incorrect: 0 (0.0%)   Distance correct but not date: 0 (0.0%)   Date correct but not distance: 0 (0.0%)   Successfully predicted: 0 (0.0%)

Below is the list of asteroids that have come close to Earth in 2021.

A list of known near-Earth asteroid close approaches less than 1 lunar distance (0.0025696 AU (384,410 km; 238,860 mi)) from Earth in 2021, based on the close approach database of the Center for Near-Earth Object Studies (CNEOS).^[1]

For reference, the radius of Earth is about 0.0000426 AU (6,370 km; 3,960 mi) or 0.0166 lunar distances. Geosynchronous satellites have an orbit with semi-major axis length of 0.000282 AU (42,200 km; 26,200 mi) or 0.110 lunar distances.

The largest asteroid to pass within 1 LD of Earth in 2021 was 2021 SG with an estimated diameter of around 68 meters and an absolute magnitude of 24.0. The fastest asteroid to pass within 1 LD of Earth in 2021 was 2021 UA₇ that passed Earth with a velocity with respect to Earth of 27.7 km/s (62,000 mph).^{[2][note 2]}

The CNEOS database of close approaches lists some close approaches a full orbit or more before the discovery of the object, derived by orbit calculation. The list below only includes close approaches that are evidenced by observations, thus the pre-discovery close approaches would only be included if the object was found by precovery, but there was no such close approach in 2021.

This list and the relevant databases do not consider impacts as close approaches, thus this list does not include any of the objects that collided with Earth's atmosphere in 2021, none of which were discovered in advance, but were observed visually or recorded by sensors designed to detect detonation of nuclear devices.

     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 highlighted green indicate objects discovered more than one week before closest approach

     Rows highlighted turquoise indicate objects discovered more than 7 weeks 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)

This sub-section visualises the warning times of the close approaches listed in the table of confirmed close approaches, depending on the size of the asteroid. It shows the effectiveness of asteroid warning systems at detecting close approaches in 2021. The sizes of the charts show the relative sizes of the asteroids to scale. For comparison, the approximate size of a person is also shown. This is based the absolute magnitude of each asteroid, an approximate measure of size based on brightness.^[1]

Absolute magnitude H ≥ 30 (smallest)

(size of a person for comparison)

Absolute magnitude 30 > H ≥ 29

Absolute magnitude 29 > H ≥ 28

Absolute magnitude 28 > H ≥ 27

Absolute magnitude 27 > H ≥ 26 (probable size of the Chelyabinsk meteor)

Absolute magnitude 26 > H ≥ 25

Absolute magnitude 25 > H (largest)

•   After closest approach: 1 (100.0%)
•   < 24 hours before: 0 (0.0%)
•   up to 7 days before: 0 (0.0%)
•   > one week before: 0 (0.0%)
•   > 7 weeks before: 0 (0.0%)
•   > one year before: 0 (0.0%)

Below is the list of predicted close approaches of near-Earth asteroids larger than magnitude 27, that were predicted to occur in 2021.^{[note 1]} This relates to the effectiveness of asteroid cataloging systems at predicting close approaches in 2021. 2018 BA₃ (with a 9 day observation arc from January 2018) could have passed as far as 3 million km (8 LD) from Earth.^[21]

For asteroids which were observed but not predicted in advance, see the main list above.

  Rows highlighted orange indicate objects which were predicted theoretically but were not observed in practice

  Rows highlighted yellow indicate objects which were predicted and observed but the predicted close approach date and distance were incorrect

  Rows highlighted green indicate objects which were observed with the predicted close approach distance (within +/-50%) but wrong date

  Rows highlighted turquoise indicate objects which were observed with the predicted close approach date but wrong distance (out by over 50%)

  Rows highlighted blue indicate objects which were observed as predicted with the correct close approach date and distance

Below is an example list of near-Earth asteroids that passed or will pass more than 1 lunar distance (384,400 km or 0.00256 AU) from Earth in 2021.

• List of asteroid close approaches to Earth
• List of asteroid close approaches to Earth in 2020
• List of asteroid close approaches to Earth in 2022
• Asteroid impact prediction