Asteroid 2017 MB1 passed by the Earth at a distance of about 8 785 000 km (22.8 times the average distance between the Earth and the Moon, or 5.87% of the distance between the Earth and the Sun), slightly before 8.45 am GMT on Saturday 22 July 2017. There was no danger of the asteroid hitting us, though were it to do so it would have presented a considerable threat. 2017 MB1 has an estimated equivalent diameter of 330-1000 m (i.e. it is estimated that a spherical object with the same volume would be 330-1000 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 200 000-2 750 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater 5-15 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 MB1. Minor Planet Center.
2017 MB1 was discovered on 19 June 2017 (34 days before its closest approach to the Earth) by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2017 MB1 implies that the asteroid was the 27th object (object B1) discovered in the second half of June 2017 (period 2017 M).
2017 MB1 has a 1334 day orbital period and an eccentric orbit tilted at an angle of 8.51° to the plane of the Solar System, which takes it from 0.59 AU from the Sun (i.e. 59% of he average distance at which the Earth orbits the Sun, somewhat less the distance at which the planet Venus orbits the Sun) to 4.16 AU from the Sun (i.e. 416% 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). This means that close encounters between the asteroid and Earth are extremely common, with the last having occurred in July 2016 and the next predicted in February 2025. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2017 MB1 is also classified as a Potentially Hazardous Asteroid.
2017 MB1 also has frequent close encounters with the planets Venus, which it is thought to have last passed in August 1951, and is next predicted to pass in January 2025, Mars which it last came close to in August 1955 and is next predicted to pass in April 2025), and Jupiter, which it last came close to in December 1993, and is next predicted to approach in July 2041. Asteroids which make close passes to multiple planets are considered to be in unstable orbits, and are often eventually knocked out of these orbits by these encounters, either being knocked onto a new, more stable orbit, dropped into the Sun, knocked out of the Solar System or occasionally colliding with a planet.
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