2018 GE₃

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).[lower-alpha 1] 99942 Apophis will break both of these records when it approaches only 0.098 LD (0.000252 AU) from Earth on 13 April 2029.

Trajectory past the Earth and Moon

Magnitude estimates

2018 GE₃ 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).[2][3] 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.[2]

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 GE₃ shows that this is the closest this particular asteroid has come to Earth since at least 1930.[3]

Animation of 2018 GE3's orbit

Around the Sun

Around the Earth

  2018 GE3 ·   Sun ·   Earth ·   Moon

Asteroid 2002 MN passed closer to Earth than 2018 GE₃ in 2002, and had a brighter absolute magnitude (H) of 23.6, and could be either larger or smaller than 2018 GE₃, 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.[5]

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 GE₃ measures between 48–100 meters (157–328 feet) in diameter, for an absolute magnitude of 23.8,[2] and an assumed albedo between 0.05 and 0.24, which represent typical values for carbonaceous and stony asteroids, respectively.[4]

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.[3]

As of 2018, no rotational lightcurve of 2018 GE₃ has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.[2]