Asteroid
2017 AS4 passed by the Earth at a distance of 561 900 km (1.46 times
the
average distance between the Earth and the Moon, 0.38% of the average
distance
between the Earth and the Sun), at about 5.05 pm GMT on Sunday 8
January 2017. There was no danger of the asteroid hitting us, though
had it
done so it would have presented no threat. 2017 AS4 has an estimated
equivalent diameter of 8-26 m (i.e. it is estimated that a spherical
object
with the same volume would be 8-26 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 37 and 20 km above the ground, with only
fragmentary
material reaching the Earth's surface.
The calculated orbit of 2017 AS4. Minor Planet Center.
2017 AS4 was discovered on 5 January 2017 (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 2017 AS4
implies that the asteroid was the 118th object (object S4) discovered in the first half of January 2017 (period 2017 A).
2017 AS4 is calculated to have a 1184 day orbital period and an elliptical orbit tilted at an angle of 1.95° to the plain of the Solar System that takes it from 0.69 AU from the Sun (i.e. 90% of the average distance at which the Earth orbits the Sun, slightly inside the orbit if the planet Venus) to 3.68 AU from the Sun (i.e. 368% of the average distance at which the Earth orbits the Sun, considerably more than 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 do happen occasionally, with the next predicted in January 2068.
See also...
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2017 AS4 is calculated to have a 1184 day orbital period and an elliptical orbit tilted at an angle of 1.95° to the plain of the Solar System that takes it from 0.69 AU from the Sun (i.e. 90% of the average distance at which the Earth orbits the Sun, slightly inside the orbit if the planet Venus) to 3.68 AU from the Sun (i.e. 368% of the average distance at which the Earth orbits the Sun, considerably more than 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 do happen occasionally, with the next predicted in January 2068.
See also...
