Asteroid 2017 TK1 passed by the Earth at a distance of about 6 850 000 km (17.8 times the average distance between the Earth and the Moon, or 4.58% of the distance between the Earth and the Sun), slightly after 5.20 am GMT on Sunday 1 October 2017. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2017 TK1 has an estimated equivalent diameter of 94-300 m (i.e. it is estimated that a spherical object with the same volume would be 94.300 m in diameter), and an object at the upper end of this size range 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 75 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater over 4.5 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.
The calculated orbit of 2017 TK1. Minor Planet Center.
2017 TK1 was discovered on 3 October 2017 (two days 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 2017 TK1 implies that it was the 60th asteroid (asteroid K1) discovered in the first half of October 2017 (period 2017 T).
2017 TK1 has a 1232 day orbital period and an eccentric orbit tilted at an angle of 9.94° to the plane of the Solar System, which takes it from 0.97 AU from the Sun (i.e. 97% of he average distance at which the Earth orbits the Sun) to 3.53 AU from the Sun (i.e. 353% of the average distance at which the Earth orbits the Sun, considerably more than 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). As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2017 TK1 is also classified as a Potentially Hazardous Asteroid.
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