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 2013.
This list and relevant databases do not consider impacts as close approaches, thus the list does not include any of the 24 objects that collided with Earth's atmosphere in 2013, none of which were discovered in advance, but were observed visually or recorded by sensors designed to detect detonation of nuclear devices. Of the 24 objects so detected, 5 had an impact energy greater than that of a 1 kiloton device including the 440 kiloton Chelyabinsk meteor, estimated at 20 m in diameter, which injured around 1500 people and damaged over 7000 buildings. [2][3][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 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 above table, depending on the size of the asteroid. 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.
^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.
Additional examples
Radar imaging of 2013 ET during its approach in March 2013.[31]2005 WK4 in August 2013
An example list of near-Earth asteroids that passed more than 1 lunar distance (384,400 km or 0.00256 AU) from Earth in 2013.
Plot of orbits of known potentially hazardous asteroids (size over 460 feet (140 m) and passing within 4.7 million miles (7.6×10^6 km) of Earth's orbit) as of early 2013 (alternate image).
_2005_WK4.jpg)
