Asteroid 2018 KW1 passed by the Earth at a distance of about 149 100
km (0.39 times the average distance between the Earth and the Moon, or 0.001% of the distance between the Earth and the Sun), slightly before midday
GMT on Tuesday 22 May 2018. There was no danger of
the asteroid hitting us, though were it to do so it would not have
presented a significant threat. 2018 KW1 has an estimated
equivalent
diameter of 2-6 m (i.e. it is estimated that a spherical object
with
the same volume would be 2-6 m in diameter), and an object of
this
size would be expected to explode in
an airburst (an explosion caused by superheating from friction with the
Earth's atmosphere, which is greater than that caused by simply
falling, due to the orbital momentum of the asteroid) in the atmosphere more than 40 km above the ground, with only fragmentary material
reaching the Earth's surface.
2018 KW1 was discovered on 22 May 2018 (the day of its closest approach to the Earth) by the
University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount
Lemmon in the Catalina Mountains north of Tucson. The designation 2018 KW1
implies that the asteroid was the 47th object (object W1) discovered in the second half of May 2018 (period 2018 K).
2018 KW1 has an 631 day orbital period and an eccentric orbit
tilted at an angle of 7.54° to the plane of the Solar System, which
takes it from 0.99 AU from the Sun (i.e. 99% of he average distance at
which the Earth orbits the Sun) to 1.89 AU from the Sun (i.e. 189% of
the
average distance at which the Earth orbits the Sun, and further from the Sun than the planet Mars). It is therefore
classed as an
Apollo Group Asteroid (an asteroid that is on average further from the
Sun than the Earth, but which does get closer). This means that close
encounters between the asteroid and Earth are extremely common, with the
last having occurred in August 2011 and the next predicted
in April 2027.
