Asteroid 2017 XY61 passed by the Earth at a distance of about 964 300
km (2.51 times the average distance between the Earth and the Moon, or
0.64% of the distance between the Earth and the Sun), slightly after 9.40 am
GMT on Tuesday 19 December 2017. There was no danger of
the asteroid hitting us, though were it to do so it would not have
presented a significant threat. 2017 XY61 has an estimated
equivalent
diameter of 11-34 m (i.e. it is estimated that a spherical object
with
the same volume would be 11-34 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 30 and 10 km above the ground, with only fragmentary material
reaching the Earth's surface.
The calculated orbit of 2017 XY61. Minor Planet Center.
2017 XY61 was discovered on 15 December 2017 (four 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 2017 XY61
implies that the asteroid was the 1549th object (object Y61) discovered in the first half of December 2017 (period 2017 X).
2017 XY61 has a 462 day orbital period and an eccentric orbit
tilted at an angle of 0.75° to the plane of the Solar System, which
takes it from 0.64 AU from the Sun (i.e. 64% of he average distance at
which the Earth orbits the Sun, inside the orbit of the planet Venus) to 1.69 AU from the Sun (i.e. 1.69% of
the
average distance at which the Earth orbits the Sun, more than the
distance at which the planet Mars orbits). 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 2017 XY61 has occasional close encounters with the Earth, which it last came
close to in July 2014 and is next predicted to approach in July 2019. The asteroid also has occasional close
encounters with the planet Mars, which is last passed in March 2015.
See also...
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