Asteroid 2018 SD2 passed by the Earth at a distance of about 87 860
km (0.30 times the average distance between the Earth and the Moon, or
0.006% of the distance between the Earth and the Sun), slightly after 6.05 am
GMT on Tuesday 25 September 2018. There was no danger of
the asteroid hitting us, though were it to do so it would not have
presented a significant threat. 2018 SD2 has an estimated
equivalent
diameter of 3-11 m (i.e. it is estimated that a spherical object
with
the same volume would be 3-11 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 50 and 30 km above the ground, with only fragmentary material
reaching the Earth's surface.
The calculated orbit of 2018 SD2. Minor Planet Center.
2018 SD2 was discovered on 21 September 2018 (four days before its closest approach to the Earth) by the Atlas MLO Telescope at Mauna Loa Observatory in Hawaii. The designation 2018 SD2
implies that the asteroid was the 54th object (object D2) discovered in the second half of September 2018 (period 2018 S).
2018 SD2 has a 318 day orbital period, with an elliptical orbit tilted at
an angle of 0.25° to the plain of the Solar System which takes in to
0.78 AU from the Sun (78% of the distance at which the Earth orbits the
Sun, and slightly more than the distance at which Venus orbits the Sun) and out to
1.04 AU (4%
further away from the Sun than the Earth). This means that close
encounters between the asteroid and Earth are fairly common, with the
last thought to have happened in 18 May this year and the next predicted
in July 2026. Although it does cross the Earth's
orbit and is briefly
further from the Sun on each cycle, 2018 SD2
spends most of its time
closer to the Sun than we are, and is therefore classified as an Aten
Group Asteroid. This also means that the asteroid has occasional close
encounters with the planet Venus, with the last calculated to have
occurred in September 2014, and the next predicted for November 2020.
See also...
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