Asteroid 2018 CT passed by the Earth at a distance of about 650 000 km (1.69 times the average distance between the Earth and the Moon, or 0.43% of the distance between the Earth and the Sun), slightly before 10.30 am GMT on Saturday 3 February 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 CT has an estimated equivalent diameter of 13-41 m (i.e. it is estimated that a spherical object with the same volume would be 13-41 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 2018 CT. Minor Planet Center.
2018 CT was discovered on 4 February 2018 (the day after its closest approach to the Earth) by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2018 CT implies that it was the 19th asteroid (asteroid T) discovered in the first half of February 2018 (period 2018 C).
2018 CT has a 521 day orbital period and an eccentric orbit tilted at an angle of 33.9° to the plane of the Solar System, which takes it from 0.94 AU from the Sun (i.e. 94% of he average distance at which the Earth orbits the Sun) to 1.59 AU from the Sun (i.e. 159% of the average distance at which the Earth orbits the Sun, and further 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). This means that 2018 has occasional close encounters with the Earth, with the last having happened in August 2017, and the next predicted for August 2027.
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