Asteroid 2018 HL2 passed by the Earth at a distance of about 18 775 000
km (48.9 times the average distance between the Earth and the Moon, or 12.5% of the distance between the Earth and the Sun), slightly before 5.55 pm
GMT on Sunday 13 May 2018. There was no danger of
the asteroid hitting us, though were it to do so it would have
presented a significant threat. 2018 HL2 has an estimated
equivalent
diameter of 110-340 m (i.e. it is estimated that a spherical object
with
the same volume would be 110-340 m in diameter), and an object of this
size would be predicted to be capable of
passing through the Earth's
atmosphere relatively intact, impacting the ground directly with an
explosion that would be 600 to 75 000 000 times as powerful as the
Hiroshima
bomb. Such an impact would result in an impact crater 1.5-5 km
in
diameter
and devastation on a global scale, as well as climatic effects that
would last years or even decades.
The calculated orbit of 2018 HL2. Minor Planet Center.
2018 HL2 was discovered on 26 April 2018 (17 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 HL2
implies that the asteroid was the 61st object (object L2) discovered in the second half of April 2018 (period 2018 H).
2018 HL2 has a 788 day orbital period and an eccentric orbit
tilted at an angle of 33.5° to the plane of the Solar System, which
takes it from 0.89 AU from the Sun (i.e. 89% of he average distance at
which the Earth orbits the Sun) to 2.45 AU from the Sun (i.e. 245% of
the
average distance at which the Earth orbits the Sun, and much 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). As an asteroid probably larger than 150 m in diameter
that occasionally comes within 0.05 AU of the Earth, 2018 HL2 is also
classified as a Potentially Hazardous Asteroid. 2018 HL2 has
occasional close encounters with the planet Earths, with the next predicted for May 2154.
See also...
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