Asteroid 2018 MG7 passed by the Earth at a distance of about 3 605 000 km (9.40 times the average distance between the Earth and the Moon, or 2.41% of the distance between the Earth and the Sun), slightly before 9.25 pm GMT on Saturday 23 June 2018. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2018 MG7 has an estimated equivalent diameter of 110-340 m (i.e. it is estimated that a spherical object with the same volume would be 110-340 m in diameter), and an object of this size 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 600 to 88 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater 1.5-5 km in diameter and devastation on a global scale, as well as climatic effects that would last years or even decades.
The calculated orbit of 2018 MG7. Minor Planet Center.
2018 MG7 was discovered on 20 June 2018 (three days before its closest approach to the Earth) by the Southern Observatory for Near Earth Asteroids Research (SONEAR) at Oliviera in Minas Gerais State, Brazil. The designation 2018 MG7 implies that it was the 182nd asteroid (asteroid G7) discovered in the second half of June 2018 (period 2018 M).
2018 MG7 has a 318 day orbital period, with an elliptical orbit tilted at an angle of 25.1° to the plain of the Solar System which takes in to 0.61 AU from the Sun (61% of the distance at which the Earth orbits the Sun and considerably inside the orbit of the planet Venus) and out to 1.21 AU (21% further away from the Sun than the Earth). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in November 2017 and the next predicted in January 2024. 2018 MG7 also has frequent close encounters with the planet Venus, with the last thought to have occurred in December 2010 and the next predicted for May 2021. Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2018 MG7 spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid. As an asteroid possibly larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2018 MG7 is also classified as a Potentially Hazardous Asteroid.
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