Asteroid 2017 WT12 passed by the Earth at a distance of about 1 135 000 km (2.95 times the average distance between the Earth and the Moon, or 0.76% of the distance between the Earth and the Sun), at about 5.00 pm GMT on Saturday 25 November 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 W12 has an estimated equivalent diameter of 7.23 m (i.e. it is estimated that a spherical object with the same volume would be 7.23 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 37 and 20 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2017 WT12. Minor Planet Center.
2017 WT12 was discovered on 19 November 2017 (six days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2017 WT12 implies that it was the 319th asteroid (asteroid T12) discovered in the second half of November 2017 (period 2017 W).
2017 WT12 has a 976 day orbital period and an eccentric orbit tilted at an angle of 9.43° to the plane of the Solar System, which takes it from 0.80 AU from the Sun (i.e. 80% of he average distance at which the Earth orbits the Sun) to 3.04 AU from the Sun (i.e. 304% of the average distance at which the Earth orbits the Sun, slightly more than twice 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).
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