Asteroid 2018 NM passed by the Earth at a distance of about 536 600 km (1.40 times the average distance between the Earth and the Moon, or 0.36% of the distance between the Earth and the Sun), slightly before 5.30 am GMT on Tuesday 17 July 2018. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2018 NM has an estimated equivalent diameter of 9-31 m (i.e. it is estimated that a spherical object with the same volume would be 9-31 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 33 and 15 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2018 NM. Minor Planet Center.
2018 NM was discovered on 4 July 2018 (13 days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope. The designation 2018 NM implies that the asteroid was the 12th object (object M) discovered in the first half of Jul 2018 (period 2018 N).
2019 NM has a 673 day orbital period and an eccentric orbit tilted at an angle of 1.73° 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 2.03 AU from the Sun (i.e. 203% of the average distance at which the Earth orbits the Sun, and further 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). This means that the asteroid has occasional close encounters with the Earth, with the last thought to have occurred in June 2007.
Follow Sciency Thoughts on Facebook.