Asteroid 2018 BT6 passed by the Earth at a distance of about 7 010 000 km (18.2 times the average distance between the Earth and the Moon, or 4.69% of the distance between the Earth and the Sun), slightly after 9.50 pm GMT on Friday 26 January 2018. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2018 BT6 has an estimated equivalent diameter of 100-330 m (i.e. it is estimated that a spherical object with the same volume would be 100-330 m in diameter), and an object of this size would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground directly with an explosion that would be 225 to 8800 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater 1-5 km in diameter and devastation on a global scale, as well as climatic effects that would last years or even decades.
The calculated orbit of 2018 BT6. Minor Planet Center.
2018 BT6 was discovered on 27 January 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 BT6 implies that it was the 169th asteroid (asteroid T6) discovered in the second half of January 2018 (period 2018 B).
2018 BT6 has a 1237 day orbital period and an eccentric orbit tilted at an angle of 3.01° to the plane of the Solar System, which takes it from 0.39 AU from the Sun (i.e. 39% of he average distance at which the Earth orbits the Sun, and inside the orbit of the planet Mercury) to 4.12 AU from the Sun (i.e. 412% of the average distance at which the Earth orbits the Sun, and considerably more than twice as far 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). As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2018 BT6 is also classified as a Potentially Hazardous Asteroid.
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