Asteroid 2018 UL passed by the Earth at a distance of about 220 960
km (0.57 times the average distance between the Earth and the Moon, or 0.14% of the distance between the Earth and the Sun), slightly before
11.35 am
GMT on Wednesday 17 October 2018. There was no danger of
the asteroid hitting us, though were it to do so it would have
presented a significant threat. 2018 UL has an estimated
equivalent
diameter of 2-8 m (i.e. it is estimated that a spherical object
with
the same volume would be 2-8 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 35 km above the ground, with only fragmentary material
reaching the Earth's surface.
The calculated orbit of 2018 UL. Minor Planet Center.
2018 UL was discovered on 18 October 2018 (the day after its closest approach to the Earth) by the University of Arizona's Catalina Sky Survey,
which is located in the Catalina Mountains north of Tucson. The
designation 2018 UL implies that it was the eleventh asteroid (asteroid L)
discovered in the second half of October 2018 (period 2018 U).
2018 UL has a 569 day orbital period and an eccentric orbit
tilted at an angle of 0.76° to the plane of the Solar System, which
takes it from 0.97 AU from the Sun (i.e. 97% of he average distance at
which the Earth orbits the Sun) to 1.72 AU from the Sun (i.e. 172% 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 January 2006 and the next predicted
in January 2020. 2018 UL also has
occasional close encounters with the planet Mars, with the last having
occurred in December 1952 and the next predicted for November 2036.
See also...
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