# 2018 GE3

2018 GE$_3$ is a sub-kilometer asteroid on a highly eccentric orbit, classified as a near-Earth object of the Apollo group, approximately 48–110 meters (160–360 feet) in diameter. It was first observed on 14 April 2018, by astronomers with the Catalina Sky Survey one day prior to its sub-lunar close encounter with Earth at 0.5 lunar distance. It is one of the largest known asteroids (possibly the largest) in observational history to ever pass that close to Earth (also see list).

## Orbit and classification

2018 GE$_3$ is a member of the near-Earth population of asteroids known as Apollos. Apollo asteroids cross the orbit of Earth and are the largest group of near-Earth objects with nearly 10 thousand known members. Based on an observation arc of 4 days, it orbits the Sun at a distance of 0.3–3.4 AU once every 2 years and 6 months (918 days; semi-major axis of 1.85 AU). Its orbit has an unusually high eccentricity of 0.83 and an inclination of 9° with respect to the ecliptic. It is also a Mercury-, Venus- and Mars-crosser, reaching its furthest point from the Sun in the outer asteroid belt. The body's observation arc begins at Steward Observatory's Catalina Station with its first observation in April 2018.

### Close encounters

In observational history, and other than possibly 2002 MN and 2017 VW13, this asteroid is the largest known object to ever pass that close to Earth, as well as the Moon (also see History of closest approaches of large near-Earth objects). 99942 Apophis will break both of these records when it approaches only 0.098 LD (0.000252 AU) from Earth on 13 April 2029.

#### 2018 flyby

2018 GE$_3$ was first observed on 14 April 2018, at 09:23 UT by astronomers at Steward Observatory's Catalina Station, Arizona, the day prior to its close encounter with Earth.
It had been more than 120 degrees from the Sun since March 2018, but was simply too far and too faint to be detected by automated surveys. Despite coming from directly away from the Sun, it was not discovered until 14 April 2018, only one day prior to its closest approach. If the most advanced survey telescopes had been looking at its location, it could have been discovered as early as 30 March. On 15 April 2018, at 06:41 UT, this object passed Earth at a nominal distance of 0.50 LD (0.001289 AU) which corresponds to a distance of 193,000 kilometres (120,000 miles), at a speed of 29.5 km/s (66,000 mph). The object also approached the Moon at an even closer distance of 0.34 LD (0.00087 AU) a few hours later, at 09:59 UT.
It was the 32nd known asteroid to flyby Earth within 1 lunar distance (LD) since the start of 2018 and 16th closest, although it was the largest known asteroid to pass within half a lunar distance. After closest approach its apparent magnitude dropped from 12 to 35 in less than 12 hours, heading towards the Sun. Coming from the opposite direction, it would have been impossible to observe before its approach. A preliminary analysis of the orbit of 2018 GE$_3$ shows that this is the closest this particular asteroid has come to Earth since at least 1930.

#### Historical close encounters

| NEO | Date | Approach distance in lunar distances | Approach distance in lunar distances | Approach distance in lunar distances | Abs. mag (H) | Diameter $^{(C)}$ (m) | Ref $^{(D)}$ |
| NEO | Date | Nominal$^{(B)}$ | Minimum | Maximum | Abs. mag (H) | Diameter $^{(C)}$ (m) | Ref $^{(D)}$ |
| (152680) 1998 KJ9 | 1914-12-31 | 0.606 | 0.604 | 0.608 | 19.4 | 279–900 | data |
| (458732) 2011 MD5 | 1918-09-17 | 0.911 | 0.909 | 0.913 | 17.9 | 556–1795 | data |
| (163132) 2002 CU11 | 1925-08-30 | 0.903 | 0.901 | 0.905 | 18.5 | 443–477 | data |
| 2010 VB1 | 1936-01-06 | 0.553 | 0.553 | 0.553 | 23.2 | 48–156 | data |
| 2002 JE9 | 1971-04-11 | 0.616 | 0.587 | 0.651 | 21.2 | 122–393 | data |
| 2013 UG1 | 1976-10-17 | 0.854 | 0.853 | 0.855 | 22.3 | 73–237 | data |
| 2012 TY52 | 1982-11-04 | 0.818 | 0.813 | 0.822 | 21.4 | 111–358 | data |
| 2012 UE34 | 1991-04-08 | 0.847 | 0.676 | 1.027 | 23.3 | 46–149 | data |
| 2017 VW13 | 2001-11-08 | 0.373 | 0.316 | 3.236 | 20.7 | 153–494 | data |
| 2002 MN | 2002-06-14 | 0.312 | 0.312 | 0.312 | 23.6 | 40–130 | data |
| (308635) 2005 YU55 | 2011-11-08 | 0.845 | 0.845 | 0.845 | 21.9 | 320–400 | data |
| 2011 XC2 | 2011-12-03 | 0.904 | 0.901 | 0.907 | 23.2 | 48–156 | data |
| 2018 AH | 2018-01-02 | 0.773 | 0.772 | 0.773 | 22.5 | 67–216 | data |
| 2018 GE3 | 2018-04-15 | 0.502 | 0.501 | 0.503 | 23.7 | 35–135 | data |
| 2010 WC9 | 2018-05-15 | 0.528 | 0.528 | 0.528 | 23.5 | 42–136 | data |
| (153814) 2001 WN5 | 2028-06-26 | 0.647 | 0.647 | 0.647 | 18.2 | 921–943 | data |
| 99942 Apophis | 2029-04-13 | 0.0989 | 0.0989 | 0.0989 | 19.7 | 310–340 | data |
| 2012 UE$_{34}$ | 2041-04-08 | 0.283 | 0.274 | 0.354 | 23.3 | 46–149 | data |
| 2015 XJ351 | 2047-06-06 | 0.789 | 0.251 | 38.135 | 22.4 | 70–226 | data |
| 2007 TV18 | 2058-09-22 | 0.918 | 0.917 | 0.919 | 23.8 | 37–119 | data |
| 2005 WY55 | 2065-05-28 | 0.865 | 0.856 | 0.874 | 20.7 | 153–494 | data |
| (308635) 2005 YU55 | 2075-11-08 | 0.592 | 0.499 | 0.752 | 21.9 | 320–400 | data |
| (456938) 2007 YV56 | 2101-01-02 | 0.621 | 0.615 | 0.628 | 21.0 | 133–431 | data |
| 2007 UW1 | 2129-10-19 | 0.239 | 0.155 | 0.381 | 22.7 | 61–197 | data |
| 101955 Bennu | 2135-09-25 | 0.531 | 0.507 | 0.555 | 20.19 | 472–512 | data |
| (153201) 2000 WO107 | 2140-12-01 | 0.634 | 0.631 | 0.637 | 19.3 | 427–593 | data |
| 2009 DO111 | 2146-03-23 | 0.896 | 0.744 | 1.288 | 22.8 | 58–188 | data |
| (85640) 1998 OX4 | 2148-01-22 | 0.771 | 0.770 | 0.771 | 21.1 | 127–411 | data |
| 2011 LT17 | 2156-12-16 | 0.998 | 0.955 | 1.215 | 21.6 | 101–327 | data |
| $^{(A)}$ This list includes near-Earth approaches of less than 1 lunar distances (LD) of objects with H brighter than 24. $^{(B)}$ Nominal geocentric distance from the center of Earth to the center of the object (Earth has a radius of approximately 6,400 km). $^{(C)}$ Diameter: estimated, theoretical mean-diameter based on H and albedo range between 0.05 and 0.25. $^{(D)}$ Reference: data source from the JPL SBDB, with AU converted into LD (1 AU≈390 LD) $^{(E)}$ Color codes: unobserved at close approach observed during close approach upcoming approaches Note: All close approaches between 1900 and 2200 are listed (with H<24 at less than 1 LD). Objects not observed during the approach, and simply estimated to have approached on this date, are colored grey. Generically estimated asteroid diameters are given in italics. ||||||||
Asteroid 2002 MN passed closer to Earth than 2018 GE$_3$ in 2002, and had a brighter absolute magnitude (H) of 23.6, and could be either larger or smaller than 2018 GE$_3$, depending on their albedos and thus exact sizes. 2017 VW13 (H=20.7) may have also passed closer in 2001, although the distance of its approach is very uncertain and it was not discovered until 2017.

## Physical characteristics
### Diameter and albedo

The diameter can only be estimated based on the brightness and distance. The albedo is currently unknown. Based on a generic magnitude-to-diameter conversion, 2018 GE$_3$ measures between 48–100 meters (157–328 feet) in diameter, for an absolute magnitude of 23.8, and an assumed albedo between 0.05 and 0.24, which represent typical values for carbonaceous and stony asteroids, respectively.
This asteroid is about three to six times the diameter of the meteor that exploded in the skies above Chelyabinsk, Russia in February 2013, which damaged over 7,200 buildings and injured 1,500 people, mostly from flying glass. If an asteroid of this size were to enter Earth's atmosphere, a good portion of it would likely disintegrate due to friction with the air. The remnants could survive entry however and impact the surface, thus causing regional damage dependent on various factors such as composition, speed, entry angle, and location of impact.

### Rotation period

As of 2018, no rotational lightcurve of 2018 GE$_3$ has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.

## Numbering and naming

This minor planet has neither been numbered nor named.