Asteroid 2017 KH5 passed by the Earth at a distance of 509 200 km
(1.32 times the average distance between the Earth and the Moon, 0.34%
of
the average distance between the Earth and the Sun), slightly before 4.25 pm GMT
on Thursday 25 May 2017. There was no danger of the asteroid
hitting us, though had it done so it would have presented no threat.
2017 KH5 has an estimated equivalent diameter of 5-19 m (i.e. it is
estimated that a spherical object with the same volume would be 5-19 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 40 and 25 km above the ground, with only fragmentary material
reaching the Earth's surface.
The calculated orbit of 2017 KH5. Minor Planet Center.
2017 KH5 was discovered on 25 May 2017 (the day 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 2017 KH5
implies that the asteroid was the 133rd object (object H5) discovered in the second half of May 2017 (period 2017 K).
2017 KH5 has an 862 day orbital period and an eccentric orbit
tilted at an angle of 7.85° to the plane of the Solar System, which
takes it from 0.80 AU from the Sun (i.e. 80% of he average distance at
which the Earth orbits the Sun)
to 2.74 AU from the Sun (i.e. 274% of
the
average distance at which the Earth orbits the Sun, considerably over
twice the distance at which the planet Mars 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 close
encounters between the asteroid and Earth are common, with the
last having occurred in May 1981 and the next predicted for October 2064. 2017 KH5 also has occasional close encounters with the planet Mars, with the next predicted for September 2135.
See also...
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