Asteroid 2018 NM passed by the Earth at a distance of about 536 600
km (1.40 times the average distance between the Earth and the Moon, or
0.36% of the distance between the Earth and the Sun), slightly before 5.30 am
GMT on Tuesday 17 July 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 NM has an estimated
equivalent
diameter of 9-31 m (i.e. it is estimated that a spherical object
with
the same volume would be 9-31 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 33 and 15 km above the ground, with only fragmentary material
reaching the Earth's surface.
The calculated orbit of 2018 NM. Minor Planet Center.
2018 NM was discovered on 4 July 2018 (13 days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope. The designation 2018 NM
implies that the asteroid was the 12th object (object M) discovered in the first half of Jul 2018 (period 2018 N).
2019 NM has a 673 day orbital period and an eccentric orbit
tilted at an angle of 1.73° 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 2.03 AU from the Sun (i.e. 203% 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 the asteroid has occasional close encounters with the Earth, with the last thought to have occurred in June 2007.
See also...
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