Asteroid 2017 MC1 passed by the Earth at a distance of 967 600 km (2.52 times the average distance between the Earth and the Moon, or 0.65% of the average distance between the Earth and the Sun), at about 9.25 pm GMT on Friday 30 June 2017. There was no danger of the asteroid hitting us, though had it done so it would have presented only a minor threat. 2017 MC1 has an estimated equivalent diameter of 25-78 m (i.e. it is estimated that a spherical object with the same volume would be 25-78 m in diameter), and an object towards the upper end of this range 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 about 2 km above the ground, with an explosive force about 1150 times as large as that of the Hiroshima bomb; not large enough to cause long-lasting global problems, but fairly devastating for anyone directly underneath.
The calculated orbit of 2017 MC1. Minor Planet Center.
2017 MC1 was discovered on 20 June 2017 (10 days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2017 MC1 implies that it was the 28th asteroid (asteroid C1) discovered in the second half of June 2017 (2017 M).
2017 MC1 has a 1656 day orbital period and an eccentric orbit tilted at an angle of 0.88° to the plane of the Solar System, which takes it from 0.95 AU from the Sun (i.e. 95% of he average distance at which the Earth orbits the Sun) to 4.53 AU from the Sun (i.e. 453% of the average distance at which the Earth orbits the Sun, and over three times the orbit of 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 close encounters between 2017 MC1 and the Earth are not particularly common, though the asteroid does occasionally pass close to Jupiter, with this last having happened in November 2014.
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