List of asteroid close approaches to Earth in 2018

Below is the list of asteroid close approaches to Earth in 2018.

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 2018, based on the close approach database of the Center for Near-Earth Object Studies (CNEOS).

For reference, the radius of Earth is approximately 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. Five asteroids (2018 BD, 2018 PD20, 2018 UA, 2018 WG, and 2018 WV1) are confirmed to have passed within this distance, and unconfirmed or confirmed but poorly observed asteroids A106fgF, A107j4q, ZB0A262, 2018 DN₄, ZGBE54F, A1080DC 2018 VQ₁₀, ZW87F01, and ZW900BE may have also passed within this distance.

The largest asteroid to pass within 1 LD of Earth in 2018 was 2018 AH with an estimated diameter of around 137 meters and an absolute magnitude of 22.5. The fastest asteroid to pass within 1 LD of Earth in 2018 was 2018 GE3 that passed Earth with a velocity with respect to Earth of 29.6 km/s (66,000 mph).

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 are only included if the object was found by precovery.

This list and relevant databases do not consider impacts as close approaches, thus this list does not include 2018 LA, an asteroid which was predicted to impact on Earth and burned up in its atmosphere, as well as several more objects that collided with Earth's atmosphere in 2018 which weren't 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)

In addition to the confirmed asteroids on the above list, which feature in the CNEOS close approach database, there have been well-observed unconfirmed or confirmed but poorly observed objects with a 50% or greater chance of passing within 1 LD of the Earth, which are listed separately below.

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. 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)

(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

Absolute magnitude 26 > H ≥ 25

Absolute magnitude 25 > H (largest)

•   After closest approach: 1 (25.0%)
•   < 24 hours before: 0 (0.0%)
•   up to 7 days before: 2 (50.0%)
•   > one week before: 0 (0.0%)
•   > 7 weeks before: 0 (0.0%)
•   > one year before: 1 (25.0%)

The number of asteroids listed here are significantly less than those of asteroids that approach Earth for several reasons. Asteroids that approach Earth not only move faster, but are brighter and are easier to detect with modern surveys because:

• Asteroids that come closer to Earth are a higher priority to confirm, and only confirmed asteroids are listed with a lunocentric approach distance.
• Those that closely approach the Moon are frequently lost in its glare, making them harder to confirm. They are similarly hard to discover during the new moon, when the Moon is too close to the Sun to detect asteroids while they are near the Moon.

These factors severely limit the amount of Moon-approaching asteroids, to a level many times lower than the asteroids detected passing as close to Earth.

An example list of near-Earth asteroids that passed more than 1 lunar distance (384,400 km or 0.00256 AU) from Earth in 2018.

List of asteroids that are listed on the Sentry Risk Table because they have short observation arcs with poorly constrained orbits and have a chance of impacting Earth in 2018. Given a short observation arc, many different orbits fit the observed data. These objects could be millions if not billions of kilometers from Earth on the date of a low probability virtual impactor. For example, 2005 TM₁₇₃ is expected to be 5 AU (700 million km) from Earth in December 2018 around the time of the 3 virtual impactors. 2010 GZ60 was removed from the sentry table in February 2018 after further observations were found by NEOWISE, ruling out any possible impacts.

Cumulatively among the asteroids listed below, there is a roughly 1 in 98,700 chance that any of the asteroids will impact Earth in 2018. Most of this comes from asteroid 2008 US which is only ~2 meters in diameter and had a 1 in 240,000 chance of impact on 18 April 2018.

Also included are asteroids discovered before impact (specifically, 2018 LA) and exceptionally massive fireballs with either an equivalent yield of more than 1 kiloton of TNT or an estimated size of more than 3 meters.

• List of asteroid close approaches to Earth
• List of asteroid close approaches to Earth in 2017
• List of asteroid close approaches to Earth in 2019
• List of bolides (asteroids and meteoroids that impacted Earth)
• Asteroid impact prediction

• Near-Earth object close approaches ±30 days within 5 LD (JPL)
• Upcoming close approaches to Earth (ESA)
• Table of Asteroids Next Closest Approaches to the Earth (Sormano Observatory)