Asteroid 2017 OL1 passed by the Earth at a distance of about 5 697 000 km (14.8 times the average distance between the Earth and the Moon, or 3.81% of the distance between the Earth and the Sun), at about 2.20 am GMT on Sunday 23 July 2017. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2017 OL1 has an estimated equivalent diameter of 82-270 m (i.e. it is estimated that a spherical object with the same volume would be 82-270 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 60 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater about 4 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 OL1. Minor Planet Center.
2017 OL1 was discovered on 21 July 2017 (two days before its closest approach to the Earth) by the Atlas MLO Telescope at Mauna Loa Observatory in Hawaii. The designation 2017 OL1 implies that the asteroid was the 36th object (object L1) discovered in the second half of July 2017 (period 2017 O).
2017 OL1 has a 1418 day orbital period and an eccentric orbit tilted at an angle of 1.33° 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 3.99 AU from the Sun (i.e. 399% of the average distance at which the Earth orbits the Sun, and almost three times as distant from the Sun as 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 (7 480 000 km) of the Earth, 2017 MB1 is also classified as a Potentially Hazardous Asteroid.
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