Asteroid 2018 HM passed by the Earth at a distance of about 1 096 000
km (2.85 times the average distance between the Earth and the Moon, or
0.72% of the distance between the Earth and the Sun), slightly before 3.50 pm
GMT on Sunday 15 April 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 HM has an estimated
equivalent
diameter of 6-21 m (i.e. it is estimated that a spherical object
with
the same volume would be 6-21 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 38 and 20 km above the ground, with only fragmentary material
reaching the Earth's surface.
The calculated orbit of 2018 HM. Minor Planet Center.
2018 HM was discovered on 18 April 2018 (three days before 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 HM
implies that the asteroid was the 12th object (object M) discovered in the second half of April 2018 (period 2018 H).
2018 HM has a 381 day orbital period and an eccentric orbit
tilted at an angle of 17.6° to the plane of the Solar System, which
takes it from 0.94 AU from the Sun (i.e. 94% of he average distance at
which the Earth orbits the Sun) to 1.11 AU from the Sun (i.e. 111% of
the
average distance at which the Earth orbits the Sun). 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 the
asteroid has occasional close encounters with the Earth, with the last thought to have happened in October 2017 and the
next predicted
in September this year.
See also...
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