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 2015.
This list and relevant databases do not consider impacts as close approaches, thus this list does not include any of the 43 objects that collided with Earth's atmosphere in 2015, none of which were discovered in advance, but were observed visually or recorded by sensors designed to detect detonation of nuclear devices.[2]
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.
Absolute magnitude H ≥ 30 (smallest)
Silhouette of man standing and facing forward
(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
After closest approach: 3 (75.0%)
< 24 hours before: 0 (0.0%)
up to 7 days before: 1 (25.0%)
> one week before: 0 (0.0%)
> 7 weeks before: 0 (0.0%)
> one year before: 0 (0.0%)
Absolute magnitude 26 > H ≥ 25
None
Absolute magnitude 25 > H (largest)
None
Notes
^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.
2015 AZ43 (~70 meters in diameter) passed 0.0197 AU (2,950,000 km; 1,830,000 mi) from Earth on 15 February 2015.
2014 YB35 (~500 meters in diameter) passed 11.7 lunar distances (4 million km) from Earth on 2015 Mar 27.
2015 FW117 (~110 meters in diameter) passed 3.6 lunar distances (1.38 million km) (3.2 lunar distances from the Moon) (1.21 million km) on 1 April 2015.
2015 HM10 (~80 meters in diameter) passed 1.15 lunar distances (440,000 km) (1.08 lunar distances from the Moon) (410,000 km) on 7 July 2015.
2015 TQ21 (~15 meters in diameter) passed 1.005 lunar distances (390,000 km) on 7 October 2015
2014 UR (~20 meters in diameter) passed 3.81 lunar distances (1.46 million km) from Earth on 18 October 2015.
2015 TB145 (~600 meters in diameter) passed 1.3 lunar distances (480,000 km) (0.74 lunar distances from the Moon) (286,000 km) on 31 October 2015.
2015 VO142 (~6 meters in diameter) passed 1.02 lunar distances (393,000 km) (0.85 lunar distances from the Moon) (327,000 km) on 24 November 2015
Risk-listed asteroid 2007 VE191 (~60 meters in diameter) was not observed when it probably passed roughly 0.5 AU (75,000,000 km; 46,000,000 mi) from Earth on 27 November 2015.
2015 YB initially calculated to make a close approach to Earth on 19 December 2015 turned out to be a much further away inner main-belt asteroid. On 31 December 2015 the asteroid received the designation 2015 YU9.
Timeline of close approaches less than one Lunar distance from the Moon in 2015
The number of asteroids listed here are significantly less than those of asteroids approaching Earth for several reasons:
Asteroids approaching Earth not only move faster, but are brighter and are easier to detect with modern surveys due to these factors
Asteroids approaching closer to Earth are higher priority to confirm, and only confirmed asteroids are listed with a lunocentric approach distance
Those which make close approaches to the Moon are frequently lost in its glare, making them harder to confirm, and are more easily discovered during the new Moon, when the Moon is too close to the Sun for any asteroids to be detected while they are near to the Moon anyway.
These factors combined severely limit the amount of Moon-approaching asteroids, to a level many times lower than the detected asteroids to pass just as close to Earth instead.
