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 () from Earth in 2021, based on the close approach database of the Center for Near-Earth Object Studies (CNEOS).
For reference, the radius of Earth is about or 0.0166 lunar distances. Geosynchronous satellites have an orbit with semi-major axis length of or 0.110 lunar distances.
The largest asteroid to pass within 1 LD of Earth in 2021 was 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 that passed Earth with a velocity with respect to Earth of .
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.
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.
Absolute magnitude H âÂÂ¥ 30 (smallest) (size of a person for comparison)
Absolute magnitude 30 > H âÂÂ¥ 29
Absolute magnitude 29 > H âÂÂ¥ 28
Absolute magnitude 28 > H âÂÂ¥ 27
Absolute magnitude 27 > H âÂÂ¥ 26 (probable size of the Chelyabinsk meteor)
Absolute magnitude 26 > H âÂÂ¥ 25
Absolute magnitude 25 > H (largest)
Below is the list of predicted close approaches of near-Earth asteroids larger than magnitude 27, that were predicted to occur in 2021. This relates to the effectiveness of asteroid cataloging systems at predicting close approaches in 2021. (with a 9 day observation arc from January 2018) could have passed as far as from Earth.
For asteroids which were observed but not predicted in advance, see the main list above.
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.