Asteroid 2017 SM2 passed by the Earth at a distance of about 309 800
km (0.81 times the average distance between the Earth and the Moon, or
0.21% of the distance between the Earth and the Sun), slightly before 7.35 am
GMT on Wednesday 20 September 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 SM2 has an estimated
equivalent
diameter of 6-21 m (i.e. it is estimated that a spherical object
with
the same volume would be 6-21 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 35 and 20 km above the ground, with only fragmentary material
reaching the Earth's surface.
The calculated orbit of 2017 RJ2 Minor Planet Center.
2017 SM2 was discovered on 17 September 2017 (three days before its closest approach to the Earth) by the Atlas MLO Telescope at Mauna Loa Observatory in Hawaii. The designation 2017 SM2
implies that the asteroid was the 62nd object (object M2) discovered in the second half of September 2017 (period 2017 S).
2017 SM2 has a 535 day orbital period and an eccentric orbit
tilted at an angle of 6.08° to the plane of the Solar System, which
takes it from 0.87 AU from the Sun (i.e. 87% of he average distance at
which the Earth orbits the Sun) to 1.70 AU from the Sun (i.e. 170% of the
average distance at which the Earth orbits the Sun, and slightly more distant 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). 2017 SM2 also
has frequent close encounters with the planet Mars, which it is
thought to have last passed in December 1940, and is next predicted to
pass in June 2027.
See also...
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