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List of asteroid close approaches to Earth in 2021

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

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Timeline of known close approaches less than one lunar distance from Earth

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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)

More information Date ofclosest approach, Discovery ...
More information Date ofclosest approach, Discovery ...

Warning times by size

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)

Silhouette of man standing and facing forward
Silhouette of man standing and facing forward

(size of a person for comparison)

After closest approach: 13 (39.4%)< 24 hours before: 10 (30.3%)up to 7 days before: 10 (30.3%)> one week before: 0 (0.0%)> 7 weeks before: 0 (0.0%)> one year before: 0 (0.0%)

Absolute magnitude 30 > H ≥ 29

After closest approach: 14 (41.2%)< 24 hours before: 5 (14.7%)up to 7 days before: 15 (44.1%)> one week before: 0 (0.0%)> 7 weeks before: 0 (0.0%)> one year before: 0 (0.0%)

Absolute magnitude 29 > H ≥ 28

After closest approach: 29 (45.3%)< 24 hours before: 16 (25.0%)up to 7 days before: 19 (29.7%)> one week before: 0 (0.0%)> 7 weeks before: 0 (0.0%)> one year before: 0 (0.0%)

Absolute magnitude 28 > H ≥ 27

ThumbAfter closest approach: 10 (71.4%)< 24 hours before: 1 (7.1%)up to 7 days before: 3 (21.4%)> one week before: 0 (0.0%)> 7 weeks before: 0 (0.0%)> one year before: 0 (0.0%)

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

ThumbAfter closest approach: 3 (27.3%)< 24 hours before: 1 (9.1%)up to 7 days before: 6 (54.5%)> one week before: 0 (0.0%)> 7 weeks before: 0 (0.0%)> one year before: 1 (9.1%)

Absolute magnitude 26 > H ≥ 25

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

Absolute magnitude 25 > H (largest)

ThumbAfter 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%)
  •   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%)

Predicted close approaches

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

More information Object, Predicted Date of closest approach ...

Notes

  1. [N 1]
    Absolute magnitude 27 is the estimated magnitude of the Chelyabinsk meteor, which caused widespread damage and injury, but no deaths. Objects smaller than this are excluded.
  2. [N 2]
    2021 UA7 passed Earth with a velocity with respect to Earth of 27.7 km/s and was moving away from the Sun at 37.0 km/s.
  3. [N 3]
    Discovery date, and if the object was confirmed and previously undiscovered, the discoverer
  4. [N 4]
    Distance from the center of Earth to the center of the object. See the NASA/JPL Solar System Dynamics Glossary: Geocentric. Earth has a radius of approximately 6,400 km (0.0166 LD).
  5. [N 5]
    Objects that approached closer to the Moon than Earth are marked with a check.
  6. [N 6]
    For unconfirmed asteroids, the provided distance range is for the 25th and 75th percentile. As a result, there is a 50% chance the asteroid's approach distance was outside of this range. Additionally, the uncertainty is usually asymmetric, so an asteroid at a nominal distance of 0.4-0.7 LD may have been more likely to only approach to 1.0 LD than to 0.3 LD.
  7. [N 7]
    Distance error: 0.0015 AU, approach range: 0.27 to 1.40 LD. There was a roughly 0.6% chance of impact.
  8. [N 8]
    Distance error: 0.000097 AU, approach range: 0.21 to 0.28 LD.
  9. [N 9]
    Distance error: 0.0005 AU, approach range: 0.28 to 0.66 LD.
  10. [N 10]
    Distance error: 0.00011 AU, approach range 0.037 to 0.12 LD. There was a roughly 11.7% chance of impact.
  11. [N 11]
    Distance error: 0.000082 AU, approach range: 0.55 to 0.61 LD.
  12. [N 12]
    Distance error: 0.0015 AU, approach range: 0.40 to 1.67 LD.
  13. [N 13]
    Distance error: 0.00004 AU, approach range: 0.082 to 0.11 LD.
  14. [N 14]
    Distance error: 0.0008 AU, approach range: 0.64 to 1.28 LD.
  15. [N 15]
    Distance error: 0.0000170 AU, approach range: 0.48 to 0.51 LD.
  16. [N 16]
    Distance error: >0.001 AU, approach range: 0.18 to 93 LD. Although highly asymmetric, there is still a 56% chance the asteroid passed within 2 LD of Earth, and a 15% chance it passed within 7 Earth radii of the planet.
  17. [N 17]
    Distance error: 0.000000822 AU.
  18. [N 18]
    Distance error: 0.0009 AU, approach range: 0.13 to 0.86 LD. There was a roughly 2.2% chance of impact.
  19. [N 19]
    Distance uncertainty: 0.00070 AU, approach range: 0.58 to 1.07 LD.
  20. [N 20]
    Distance error: 0.000166 AU, approach range: 0.35 to 0.48 LD.
  21. [N 21]
    Distance error: 0.0009 AU, approach range: 0.14 to 0.89 LD.
  22. [N 22]
    Distance error: 0.00078 AU, approach range: 0.077 to 0.70 LD. There was a roughly 5% chance of impact.
  23. [N 23]
    Distance error: highly asymmetric, approach range: 0.011 to 30.7 LD. There was a roughly 38% chance of impact.
  24. [N 24]
    Distance error: 0.001 AU, approach range: 0.066 to 0.86 LD. There was a roughly 12.1% chance of impact.
  25. [N 25]
    Distance error: 0.0004 AU, approach range: 0.37 to 0.68 LD.
  26. [N 26]
    Distance error: 0.00022 AU, approach range: 0.16 to 0.38 LD.
  27. [N 27]
    Distance error: 0.0010 AU, approach range: 0.61 to 1.51 LD.
  28. [N 28]
    Distance error: 0.00002 AU, approach range: 0.024 to 0.041 LD. There was a roughly 5.6% chance of impact.
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Additional examples

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More information Passed within, # ...
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Goldstone radar images of asteroid 99942 Apophis on 8–10 March 2021
Thumb
Goldstone radar images of asteroid 2001 FO32 during closest approach on 21 March 2021

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.

More information Object, Size (meters) ...

Notes

  1. [N 1]
    Short arc object that had not been observed for years and therefore the uncertainty was relatively large.
  2. [N 2]
    For comparison as closest Venus approach is 2022-Jan-08 at 103 LD. (Earth will be at perihelion on 2022-Jan-04.)
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