Asteroid 2018 US1 passed by the Earth at a distance of about 880 530
km (2.29 times the average distance between the Earth and the Moon, or
0.59% of the distance between the Earth and the Sun), slightly before 4.30 pm
GMT on Sunday 21 October 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 US1 has an estimated
equivalent
diameter of 7-23 m (i.e. it is estimated that a spherical object
with
the same volume would be 7-23 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
between 37 and 20 km above the ground, with only fragmentary material
reaching the Earth's surface.
The calculated orbit of 2018 US1. Minor Planet Center.
2018 US1 was discovered on 21 October 2018 (the day of 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 US1 implies that it was the 53rd asteroid (asteroid S1)
discovered in the second half of October 2018 (period 2018 U).
2018 US1 has a 778 day orbital period and an eccentric orbit
tilted at an angle of 8.01° to the plane of the Solar System, which
takes it from 1.00 AU from the Sun (i.e. the average distance at
which the Earth orbits the Sun) to 2.31 AU from the Sun (i.e. 231% 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 September 2003 and the next predicted
in August 2022.
See also...
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